Direct Drive and Fast Ignition Workshop 2025

UPLiFT is an ambitious programme of scientific and technological development which aims to lay the foundations to enable a future demonstration of laser inertial fusion energy. In this talk I will discuss the steps required to make progress along this path, and our current programme.

The technological developments are currently focussed on implosion target manufacturing and characterisation, and broadband, high efficiency, high repetition rate lasers which are designed specifically to reduce cost.

UPLiFT’s science is focussed on understanding the physics of direct drive, and specifically that which differentiates it from indirect drive; laser-plasma instabilities, imprint, and non-local transport. A focussed programme of inline model development, combined with dedicated experiments to benchmark the models, will de-risk implosion designs for a future laser system.

Implosion design work will evaluate both conventional direct drive, and Shock-Augmented Ignition1 approaches. Shock-Augmented Ignition is a relatively new Laser Inertial Fusion concept which, based on our work to-date, may enable higher yield with implosions that are less exposed to deleterious hydrodynamic and/or laser-plasma instabilities.

1 Scott et al, Physical Review Letters, (2022).

The perspective for future laser fusion energy is now coming to reality with great achievements in recent years. The National Laboratory on High Power Laser and Physics, dedicated to the laser confined fusion research for over 60 years, has launched an advanced direct drive program aimed at the laser fusion energy, including upgrading the present laser facility, performing related experimental campaigns, and building new larger laser facilities. We have developed a series of advanced laser and diagnostic technologies for direct drive and fast ignitions, and conducted physical experiments utilizing various spatiotemporal manipulation techniques of laser fields to meet the practical requirements for efficient laser absorption in direct drive, which enhanced our understanding of the roles of irradiation uniformity, coherence, and other optical parameters in laser-plasma interactions. These advancements provide a robust technical foundation for future in-depth research on direct drive physics.

In inertial fusion energy (IFE), the coupling efficiency of a laser into a fusion-relevant target, and consequently into inertial kinetic energy, is of critical importance for the overall efficiency of a fusion power plant. Laser-plasma instabilities (LPI), such as cross-beam energy transfer (CBET), two-plasmon decay (TPD), stimulated Brillouin scattering (SBS), and stimulated Raman back- and side-scattering (SRS, SRSS), play a significant role in the laser-plasma interaction process and therefore the laser-plasma energy coupling, because the laser intensity regime foreseen for laser-driven inertial confinement fusion is well above the threshold for such processes. Consequently, understanding and controlling LPIs is indispensable.

A current approach to mitigating LPIs is limiting the time available for their growth during the interaction between the laser and the plasma. One viable approach to addressing this challenge is the use of laser pulses with reduced temporal coherence, typically with coherence times shorter than the growth rate factor of LPIs. By rapidly changing the spectral phase and or amplitude on long pulses, the phase-matching condition for the LPI fluctuates, thereby reducing the effective interaction time between the laser and plasma waves. Spectrally, this corresponds to broadening the spectral bandwidth of the laser pulse for a given overall nanosecond profile.

In order to support studies for LPI mitigation via broadband nanosecond pulses, we implemented several measures on the neodymium-glass-based system PHELIX to adapt its architecture to this new requirement. First, a new front-end has been developed to serve as a seed for the PHELIX amplifier chain. This setup employs a Q-switched Ti:sapphire-based cavity to generate 17-nm-wide broadband 3-ns-long pulses. Due to the quantum-based initiation, the seed is inherently random, resulting in a spectrally incoherent pulse. Since the cavity is designed as a single spatial mode resonator, the beam transport of the emerging pulse is facilitated. However, as the PHELIX pre-amplifier and main amplifier chains utilize Nd:glass, spectral pre-compensation is essential to maintain the broadest possible spectrum after amplification. As a result, the output of the laser amplifier exhibits a spectrum of up to
9 nm at full width half maximum (11 nm 1/e²) at the central wavelength of 1056 nm with an energy of 150 J.
Frequency doubling of such pulses is an additional challenge. The broad bandwidth in combination with the ns pulse duration requires a special partially deuterated DKDP crystal (15%) to ensure broadband phase matching as well as high-efficiency frequency conversion. Such a crystal has been installed in the beamline that delivers the PHELIX beam to the HHT experimental area located at the output of the synchrotron SIS18, where the first experimental campaigns concerning LPI took place in 2025.

In this presentation, I will provide details on the laser development, achieved results in amplification and frequency doubling, and an outlook on the next steps required to advance the LPI mitigation studies.

The Extreme Light Infrastructure - Nuclear Physics (ELI-NP) facility hosts the world's first operational (dual-arm) 10 PW laser system, HPLS, setting new standards in ultrashort and ultra-intense laser science.
In 2024, ELI-NP achieved 67 weeks of beam delivery for users:
• 7 weeks at 100 TW output,
• 30 weeks at 1 PW output,
• 30 weeks at the 10 PW output, operated at a repetition rate of one shot per minute.
In the last 35 laser operation days in 2024, HPLS delivered 127 shots per day on average at the 10 PW output in E6 experimental area, where a gaseous target was used for experiments related to electron acceleration, Compton backscattering and muons production. It delivered a maximum of 274 shots on the 1st of November 2024, among which 258 on the gaseous target and 16 for alignment checks. This unparalleled operational record underscores ELI-NP’s capacity to enable groundbreaking research in high-power laser physics and in fusion research.
Besides the 10 PW capabilities, the HPLS provides unique features of optically synchronous 2x1 PW outputs at 1 Hz, down to 11 fs rms. The 2x1 PW outputs associated E5 experimental area was designed to make possible simultaneous production of proton and electron bunches, and their subsequent conversion in x-rays and neutrons. For the production of protons, a regenerating liquid target in vacuum was developed. When the liquid target will be implemented in the E5 experimental area, it will be the workhorse for testing the radiation hardness of inertial fusion related materials.

Direct-drive implosion experiments are being performed by CEA on the LMJ laser facility [1] for the purpose of inertial fusion research and particle source creation [2].
Here, we present preliminary results of a recent campaign in the exploding-pusher (strong shock) regime using D2-filled thin glass capsules. In this configuration, the short square laser pulse shape and the thin ablator result in moderate convergence ratios and large hot spots with high temperatures. For optimizing the beam irradiation uniformity of the LMJ laser that is not dedicated to direct-drive implosions, laser beams have been repointed in a polar direct drive (PDD) configuration [3].
Neutron and proton as well as X-ray imaging data are presented and discussed.
Finally, future experimental perspectives on the LMJ facility, in particular for investigating the compressive implosion regime, are mentioned.

References
[1] W. Cayzac et al., High Energy Density Physics 52, 101125 (2024)
[2] M. Temporal et al., J. Plasma Phys., vol. 87, 905870208 (2021)
[3] M. Temporal et al., Physics of Plasmas 21, 012710 (2014)

During the first phase of the campaign for the Double-Cone Ignition (DCI) scheme [1], a series of experiments from R1 to R8, we completed the feasibility studies on durability of implosion gold-cones, adiabatic compression and acceleration of shell targets embedded in the implosion cones [2,3], formation of high-density isochoric plasmas by optimized collision of two high speed plasma jets from the tips of the double-cone [4-6], durability of heating cone in the colliding plasma [6], generation of a fast electron beam in an optimized spectrum from the heating cone [7], propagation process of the fast electron beam from the tip of the heating cone to the colliding plasma and end-on heating process of the high-density colliding plasma. The density of the colliding plasma driven from each side by 4 implosion laser beams in 5 ns shaped pulses was measured to be over 100 g/cm^3. An optimized colliding plasma with a sharp end to the heating fast electron beam was formed with an areal density over 0.6 g/cm^2. The ion temperature of the colliding plasma was heated up from 300 eV to over 600 eV by the fast electron beam from the tip of the heating cone driven by a 500 J PW laser beam in 10 ps pulses [8]. After the first upgrading of SG-II U laser facility in 2023, we started the second phase of the campaign in a series of R9 and R10 experiments using a total of 16 implosion laser beams in 5 ns shaped pulses together with 2 heating PW laser beams in 10 ps pulses. A balanced irradiation of inner circle with outer circle of 8 implosion laser beams from each side on the enlarged shell targets in the implosion cones was achived and end-on heating process of the high-density colliding plasma was optimized [9]. R11 experiment in April of 2025 to demonstrate the combined heating process by 2 heating PW laser beams is in preparation. These results support the further upgrading plan to 32 implosion laser beams in 5 ns pulses and 4 heating PW laser beams in 10 ps pulses.

References
[1] J. Zhang et al., Double-cone ignition scheme for inertial confinement fusion, Phil. Trans. R. Soc. A 378, 20200015 (2020).
[2] H. Liu et al., Demonstration of Enhanced Direct-Drive Implosion Efficiency Using Gradient Pulses, Phys. Rev. E 105, L053203 (2022).
[3] Y. Zhang, Z. Zhang, X. Yuan, et al., Efficient energy transport throughout conical implosions, Phys. Rev. E, 109, 035205 (2024).
[4] F. Wu et al., Machine-learning guided optimization of laser pulses for direct-drive implosions, High Power Laser Science and Engineering 10, e12 (2022).
[5] K. Fang, Y. Zhang, Y. Dong, et al., Dynamical process in the stagnation stage of the double-cone ignition scheme. Phys. Plasmas 30, 042705 (2023).
[6] Z. Liu et al., Observation of the colliding process of plasma jets in the double-cone ignition scheme using an x-ray streak camera, Physics of Plasmas 31.4 (2024).
[7] G. Zhou et al., Enhanced hot electron generation via laser interference, Physics of Plasmas 29, 052704 (2022).
[8] Y. Dai et al., Diagnosing the fast-heating process of the double-cone ignition scheme with x-ray spectroscopy. High Power Laser Sci. Eng. 12, e50 (2024).
[9] B. Jiang et al., Localized end-on heating for hotspot ignition in precompressed isochoric plasmas, under review.

We present robust numerical approach for the direct simulation of complex multi-material and multiphase flows, particularly in high-energy density and fusion environments. These flows often exhibit intense shock waves, mixing instabilities, and complex thermonuclear reactions. A successful numerical approach must be stable, conservative, and capable of capturing intricate flow dynamics while minimizing computational overhead. To address these challenges, we propose a hybrid approach that integrates Eulerian Volume of Fluid (VOF) methods with large particle hydrodynamics techniques. In their original formulations, these methods do not relay on Riemann solvers, making them particularly effective for transonic flows. For regions near shock waves, Riemann solvers can be employed alongside with higher-order reconstruction and positivity-preserving limiters to prevent solution degradation. We validate the approach using standard benchmarks such as Kelvin-Helmholtz and Taylor-type instabilities. Preliminary results for multicomponent flows induced by laser and heavy ion beams are also presented.

UPLiFT (UK Programme of Laser inertial Fusion Technology for Energy) is a new UK government-funded research programme investigating inertial fusion energy. The physics strand of UPLiFT (which also features work on laser development and target fabrication) aims to investigate and develop an implosion design for a future potential IFE reactor, and as part of this aims to help address outstanding physics questions associated with direct-drive IFE such as laser imprint, LPI growth, and non-local heating. We intend to perform a number of experiments to investigate these topics over the coming years.

In this talk, current plans for some of the first UPLiFT experiments will be presented. This includes an OMEGA experiment in 2025/2026 to investigate laser imprint in the presence of SSD, and an LMJ experiment scheduled for 2027-2029 to investigate energy coupling in an ignition-relevant plasma, along with LPI growth when CBET is reduced.

Direct drive is one of the most promising fusion approaches, which could enable reaching high-gain schemes for energy production. This builds on the success of the NIF ignition results, which demonstrated an essential milestone on the inertial fusion energy roadmap.
However, facilities dedicated to basic research and training in direct drive and fast ignition are very scarce in Europe, especially when one considers that multi-kilojoule laser interaction conditions are necessary to gather impactful experimental data.
GSI has a strong tradition in plasma physics and fusion-related research that dates back to the 1980s. Currently, PHELIX is the only laser in Germany with multi-100 J capability. In addition, PHELIX has been upgraded with nanosecond broadband pulse capabilities to support experiments on LPI mitigation with such an innovative technology.
With the FLARE project, GSI proposes to build a user-oriented facility with multi-kilojoule multi-beam pico- and nanosecond-pulse capabilities to bring GSI to the next level for IFE research. This new facility should be ideally installed on the FAIR campus to enable multi-beam laser stand-alone as well as combined laser-ion experiments. One of the main feature will be the generation of laser pulses with the highest spectral bandwidth at the second and third harmonic in order to study laser-plasma instabilities, laser-plasma energy coupling and hot electron generation, as well as fast ignition with picosecond laser pulses.
In this presentation, I will review the science case for the proposed FLARE facility and the initial key parameters to support this research.

We study an amplifier scheme for inertial confinement fusion that can generate extremely hot and dense fusion fireball, increase burn efficiency, and produce additional gain via primary and secondary nuclear implosions. Very different from the central ignition scheme dominated by temperature in central hotspot, the primary explosion of the amplifier scheme is dominated by density and happens in cold shell, and the secondary explosion happens in an extremely hot and dense fireball generated by the primary explosion. Also very different from the high gain schemes of fast ignition, impact ignition, and shock ignition, there no need is for the amplifier scheme to add any ignitor shock separately. Here, we consider a laser drive of 10 MJ [Z. Sui and K. Lan, Matter Radiat. Extremes 9, 043002(2024)], and present a direct-drive amplifier design with Gabs = 164 and a central ignition design with Gabs = 29.8 for comparison, where Gabs is the ratio of fusion energy output to target absorbed laser energy. From our 1D simulations, the yield released by the amplifier capsule after bangtime is 4.88 times that before, remarkably higher than 1.25 times of the central ignition capsule. Especially, the fireball of amplifier lasts for 33 ps between the two explosions, reaching 400 g/cc, 580 keV, 100 Tbar at center when the secondary explosion happens, which leaves an important room for novel target designs towards clean fusion energy. The amplifier scheme can be realized at a relatively low convergence ratio, so it can greatly relax the RT hot spot condition and the stringent requirements on engineering issues by a high gain fusion.

Cone guided implosions enable approximately spherical implosion symmetry to be maintained while an open solid angle is kept for coupling in the ignition energy. The concept was developed at the Rutherford Appleton Laboratory with first integrated tests at the Gekko Facility subsequently.
From these early and subsequent experimental campaigns the understanding of possibilities and challenges has developed. The current state of cone guided FI is reviewed with particular attention given to controlling the shape of the accelerating spectrum.

Laser spot size is a critical parameter in direct-drive implosions. A larger spot generally improves illumination uniformity and enhances implosion sphericity, but an excessively large spot results in a significant fraction of laser energy bypassing the target ("blowby") and not being absorbed. This blowby light also seeds Cross-Beam Energy Transfer (CBET), a laser-plasma instability that reduces absorbed energy and enhances asymmetries from the beam geometry.
During the implosion, the capsule’s critical surface moves inward. A spot size that provides optimal illumination early in the pulse may become too large later in the implosion, reducing energy absorption in its final stages. Focal spot zooming is a proposed solution that dynamically decreases the spot size over time to match the critical radius trajectory, using techniques such as a flying focus. This approach could optimize both illumination uniformity and efficiency, overcoming the limitations of static spot sizes.
This work presents multi-dimensional simulations of direct-drive implosions using the CHIMERA radiation-hydrodynamics code, incorporating the SOLAS laser ray-trace and CBET package. We investigate the performance enhancement of zooming, relative to implosions with a static spot size. Improved performance derives from enhanced laser absorption, without significant degradation from beam geometry asymmetries. Simulations are also presented featuring both zooming and CBET mitigation via enhanced laser bandwidth.

Since Guderley [1] found the self-similar solution of a single spherical shock wave converging to the center in uniform matter in 1942, it has been applied to a number of different problems. The maximum compressed density of the reflected shock at the center reaches 32 times the initial density, when the specific heats ration  = 5/3. Now we have found new self-similar solutions for multi-stacked converging and diverging shocks. By increasing the number of stacked shocks, the maximum compression rate has turned out to dramatically increases; for instance, it goes beyond 1000’s with four stacked shocks propagating in a uniform spherical target. Unlike the orthodox shell-structured ICF targets, the use of spherical solid targets is expected to release us from the Rayleigh-Taylor instability. This study then gives an insight for a new and simple ignition approach to ICF. The detail of the study is provided in the talk.

[1] G. Guderley, Luftfahrtforschung 19, 302 (1942).

Double-cone ignition (DCI) scheme [1] was proposed as an alternative fast-ignition direct-drive laser fusion to achieve a high-density plateau around the compressed target center and a high laser-to-target-center energy coupling via magnetically guided heating. Since 2020 serval rounds of DCI experimental campaigns have been conducted in Shenguang II upgrade (SG-II-U) facility and its feasibility has been confirmed. To realize fusion ignition of DCI, we designed the ns implosion and ps heating laser parameters by integrated simulation, which have been applied in the phase II of the upgrading plan of SG-II-U. For this phase of facility, we designed to mix second-harmonic and fundamental ps lasers for efficient heating and electron spectrum control, based on the finding of electromagnetically induced transparency in relativistic plasma [2]. For the Phase I of the upgrading of SG-II-U, we designed the optimized ps laser angles to enhance the electron yield and spectrum hardness, based on the transverse interference of two ps lasers [3].

[1]J. Zhang, W.-M. Wang, X.-H. Yang, et al., 2020. Double-cone ignition scheme for inertial confinement fusion, Phil. Trans. R. Soc. A, 378, 20200015.
[2]Tie-Huai Zhang, Wei-Min Wang, Yu-Tong Li, and Jie Zhang, Electromagnetically Induced Transparency in the Strongly Relativistic Regime, Physical Review Letters 132, 065105 (2024).
[3]Ge Zhou, Wei-Min Wang, Yutong Li, and Jie Zhang, Enhanced hot electron generation via laser interference, Physics of Plasmas 29, 052704 (2022).

We present design studies for the scale of a fusion pilot plant that can demonstrate reliable engineering gain larger than unity by using direct drive central hot spot ignition. We use a modified version of the scaling laws obtained by Trickey et al. [1] in combination with theoretical and empirical models to constrain the implosion design space (e.g. 1d-Gain > 50). Choosing trade-offs between instability risks, i.e. for laser plasma instabilities (LPI) and hydrodynamic instabilities, we obtain points in this design space. Hydrodynamic instabilities such as the Rayleigh-Taylor instability can lead to the imploding shell breaking up or material mixing into the central hot spot. We compare the risks for hydrodynamic instabilities between designs with the stability threshold empirically found at the OMEGA laser [2]. LPIs like two-plasmon decay, stimulated Raman scattering, and cross-beam energy (CBET) transfer reduce the laser absorption efficiency and produce hot electrons that might preheat the fuel. To account for these LPI risks, we study the design space at different peak intensities ($4-10\ast {10}^{14}$ W/cm${}^2$).

Subsequently, we run detailed one-dimensional radiation-hydrodynamic simulations using the code DUED [3] to design the targets and the temporal laser pulse shapes. The laser pulses are adiabat-shaped designs with a picket, a foot, a ramp, and a peak plateau. Three spot size zooming is used to ensure good coupling of laser energy to the target and minimise CBET risk. An analysis of the simulated results will be provided and compared to the modified scaling laws. We show that parts of the used DT wetted-foam ablator can be replaced by a plastic shell to fulfil target manufacturing constraints. Finally, we identify gaps for more detailed future studies.

Abstract: In the Double-Cone Ignition (DCI) approach to inertial confinement fusion, two head-on plasmas collide at the cone tips, creating an isochoric plasma. This plasma is then rapidly heated by a beam of MeV fast electrons produced through the interaction of intense picosecond laser pulses with a gold-cone target. The temporal precision of fast electron injection plays a crucial role in determining the efficiency of the fast-heating process. Experimental demonstrations were conducted at the Shenguang-II Upgrade laser facility, employing fusion neutron detection and temporally resolved X-ray emission measurements. The experimental findings reveal that no detectable neutron signal, where the neutrons from the ablation region were eliminated with a deuterium-free ablation layer, was observed without the fast electron beam. In contrast, precisely timed injection of the fast electron beam results in a remarkable enhancement of neutron yields to 7×10^5, exceeding a factor of 10, which is approximately equivalent to 1×10^8 with the deuterium-tritium target. The ion temperature was 600 eV with a peak density of 38 g/cm^3 These results provide robust experimental validation of the high efficiency of fast heating in the DCI scheme, highlighting its potential for advancing high-gain laser fusion research.

Key Words: inertial confinement fusion, fast electron, neutron yields

A serious issue within ICF is the growth of laser plasma instabilities (LPI) which act to scatter laser light and generate hot electrons, reducing the efficiency of the implosion and hindering the fusion process. Namely, we are concerned with the growth of the Stimulated Raman Scattering (SRS), Stimulated Brillouin Scattering (SBS), and Two Plasmon Decay (TPD) instabilities. Advanced direct drive schemes such as shock ignition [1] are in particular danger of these instabilities since the growth rate scales non-linearly with laser intensity.

In laser-plasma experiments the typical approach is to measure scattered light from the SRS and SBS instabilities in the backscattered direction i.e. scattered back down the laser cone. Recent observations at the NIF [2] and OMEGA [3] facilities however identified that side-scattered Raman (SRSS), where scattered light propagates nearly perpendicular to the electron density gradient, can also play an important role in direct drive relevant regimes. A recent effort to characterise the total reflectivity of SRSS estimated a total reflectivity of ~5% of the total laser energy [4], rendering it a potentially significant source of hot electrons and reduced drive efficiency. Work remains to better understand the fundamental scaling parameters of SRSS and define the laser-plasma regimes where it can dominate, with a view of ultimately understanding how best to mitigate this LPI.

In this paper we present results from an experiment at PALS focused on studying the growth of SRSS using the “Octopus” fibre-based diagnostic to obtain angularly and spectrally resolved SRSS scattered light measurements [5]. Circular and elliptically shaped phase plates were used to explore the influence of focal spot size in directions parallel and perpendicular to the laser E-field. Both thick targets and thin “exploding foil” targets were used to explore the effect of density scale length. We show that SRSS grows more strongly along the direction perpendicular to the laser E-field and reflectivity significantly increases with longer focal spot size in this direction. Density scale length was seen to have a negligible effect on SRSS growth whilst backscattered SRS was more strongly impacted. Preliminary results from ray tracing simulations are also used to explore further the effect of the density profile on the observed angular distribution of the SRSS scattered light.

[1] R. Betti et al., PRL 98, 155001 (2007)
[2] M. J. Rosenberg et al., PRL 120, 055001 (2018)
[3] S. Hironaka et al., Phys. Plasmas 30, 022708 (2023)
[4] K. Glize et al., Phys. Plasmas 30, 122706 (2023)
[5] G. Cristoforetti, E. Hume et al., MRE (submitted)

Double-cone ignition (DCI) [1] is an alternative laser directly driven (LDD) multi-step inertial confinement fusion (ICF) scheme, starting with fuel compression and acceleration within two head-on gold cones, followed by collision of the high-density plasmas ejected from the cone tips, and finally ignited with rapid heating by fast electrons. During the direct laser irradiation phase, due to the unique target geometry and the laser configuration in the Shenguang-II Upgrade (SGII UP) laser facility, it is of primary importance to experimentally investigate the laser-plasma instabilities (LPIs) in the specific DCI laser-plasma conditions.
In this work [2], we present the results of LPI scattered light measurements during the recent experimental campaigns. A series of experiments were conducted with a set of dedicated LPI diagnostics. The overlapped laser intensity ranges from $6\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$ to $1.8\times {10}^{15}\mathrm{W}/{\mathrm{cm}}^2$, with moderate density scale length ($L_n\sim 150-300\mu \mathrm{m}$ ) and electron temperature ($T_e\sim 2-3\mathrm{keV}$) . An overall LPI scenario has been built from the collection and investigation of angularly distributed scattered light [3,4]. We find that across broad ranges of laser and plasma parameters, the dominance of the LPIs is side stimulated Raman scattering (SSRS), with significant scattered light across an extremely wide range of emission angles. Furthermore, time-resolved spectra show different SRSS temporal behaviours along different angles, and a higher threshold than TPD. An overall SRSS energy loss of up to 6% was measured. Our results also show some evidence that the “Raman gap” is scaled with the laser intensity and the plasma conditions.

Reference:
[1] Zhang, J. et al. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 378, 20200015 (2020).
[2] Zhao, X. et al. Nucl. Fusion 64, 086069 (2024).
[3] Zhao, X. et al. Rev. Sci. Instrum. 93, 053505 (2022).
[4] Zhang, Y. et al. High Power Laser Sci. Eng. 12, e84 (2024).

In laser-driven inertial confinement fusion, the compression performance is reduced by the presence of laser plasma instabilities (LPI). These reflect or scatter significant amounts of laser light and produce hot electrons that preheat the imploding shell, which reduces its compressibility. For mitigating LPI, one possible strategy is to use laser pulses with broad spectral bandwidth.
By increasing the bandwidth, the laser coherence time is reduced. This limits the time LPI has to develop, with a significant difference expected for a FWHM of Δλ/λ≈1% and higher [1,2]. But the interaction between different types of LPI and other effects make a prediction of the exact changes with increasing bandwidth difficult [3]. With a recent upgrade, the PHELIX laser at the GSI Helmholtz Centre for Heavy Ion Research can now deliver frequency doubled pulses of a ND:glass laser with variable bandwidths of up to about 0.5%. This capability was used to experimentally test the effect of an increased bandwidth on LPI.
We present preliminary results of an experiment comparing LPI driven by monochromatic and the broad bandwidths. Both types of laser pulses have a central wavelength of around 527 nm and the same temporal profile of 2 ns length.
The mechanisms of instabilities that we studied are two plasmon decay (TPD) and stimulated Brillouin and Raman scattering (SBS & SRS). Light that was backscattered through the entrance window of the laser was collimated. The typical signals produced by LPI were then measured. Side-scattered light was collected at various angles and analyzed. Preliminary results indicate a decrease in TPD and SBS and a significant increase in SRS, in particular in side-scattering directions.
Electron spectra were also measured, with diagnostics placed at several angles in front of and behind the target. Magnetic electron spectrometers and indirect measurements, by the X-ray bremsstrahlung the electrons produced, were employed. Both show increased signal with broadband pulses, suggesting an increase in the hot electron population.

[1] R. K. Follett et al., Thresholds of absolute two-plasmon-decay and stimulated Raman scattering instabilities driven by multiple broadband lasers. Phys. Plasmas 28 (3), 032103 (2021).
[2] J. W. Bates et al., Mitigation of cross-beam energy transfer in inertial-confinement-fusion plasmas with enhanced laser bandwidth. Phys. Rev. E 97 (6), 061202 (2018).
[3] Z. Liu et al., Parametric instabilities and hot electron generation in the interactions of broadband lasers with inhomogeneous plasmas. Nucl. Fusion 63 (12), 126010 (2024).

Backward stimulated Raman scattering is a three-wave coupling instability requiring the matching of an incoming pump light wave to a scattered light wave and electron plasma wave. It can be harmful to laser-driven inertial confinement fusion because of the reflection of a part of incident laser flux and the generation of suprathermal electrons that preheat the fuel. It is believed that by increasing the laser bandwidth one can suppress the excitation of Raman scattering and mitigate its detrimental effects. In this talk we discuss the previously published results where in 1D broadband radiation is shown to have little effect due to trapping effectively broadening the frequency of excited plasma waves and so also matching conditions for SRS. We then move on to 2D simulations, where trapping is not as pronounced, and find that broadband radiation alone appears to still be insufficient to prevent SRS in the kinetic regime. We also discuss some of the modelling of broadband radiation and the problems in properly predicting suppression of SBS. Finally we discuss the results from diffraction calculations for a variety of optical setups as an introduction into the next stage of this work.

The Shock Augmented Ignition (SAI) [1] approach to inertial fusion aims to assemble high areal density fuel using moderate implosion velocities, similar to Shock Ignition [2]. In doing so, it is predicted to achieve high gains while remaining hydrodynamically stable. Similar to Shock Ignition, a marginally sub-ignition hot spot is pushed beyond the ignition threshold by a late-timed shock wave. However, SAI is able to launch the shock using laser intensities much lower than those required for Shock Ignition, significantly decreasing the excitation of detrimental laser-plasma instabilities. This is achieved by first decreasing the laser power before rapidly increasing it again. Shock launching is additionally aided by the preconditioning of the ablation plasma from the reduction in laser power.

This talk will outline the results from a series of implosions that were performed on the Omega laser facility, designed to demonstrate the efficacy of the augmenting shock in improving implosion performance. Using energy-equivalent laser pulses, the timing of the shock launch was varied by changing the timing of the dip and increase in the laser power. Key implosion performance metrics were improved through the optimisation of the shock launch timing. The optimal range for the experimental results was consistent with the simulated predictions and followed the same trends. Optimally timed shots saw increases in areal density, yield, and hot spot pressure of 50%, 65% and 112% respectively.

These results, along with ignition-scale SAI simulations, suggest that the critical design feature for SAI is the timing of the shock arrival at the hot spot centre with respect to the peak in the compressive yield. Maximum performance is found for shock arrivals just prior to this peak, with simulations predicting an ignition cliff for shocks arriving after this.

[1] - R. Scott, D. Barlow, W. Trickey, A. Ruocco, K. Glize, L. Antonelli, M. Khan, and N. Woolsey, Shock-augmented ignition approach to laser inertial fusion, Physical Review Letters 129, 195001 (2022).
[2] - R. Betti, C. Zhou, K. Anderson, L. Perkins, W. Theobald, and A. Solodov, Shock ignition of thermonuclear fuel with high areal density, Physical Review Letters 98, 155001 (2007).

The Abalative Rayleigh–Taylor instability grows in laser-induced high density plasma greatly affected the ignition of inertial confinement fusion. Recently, we have studied numericaly the effect of laser wavelengths on the growth of ARTI. We found that shorter laser wavelength leads to higher coupling efficiency between laser and kinetic energy of the implosion fluid. The ARTI growth rate decreases as the wavelength moves from 150nm towards the extreme ultraviolet, reaching the minimum near at the wavelength λ =65nm. As the wavelength continues to move from 50 nm towards the soft X-rays, the ARTI growth rate increases rapidly.
By dividing the incident laser into a spatially uniform part with λ = 351nm and spacemodulated part with certain wavelength, another 2D model simulation shows that the ARTI growth rate decreases as the wavelength of space-modulated laser becomes shorter, and ata certain wavelength, ARTI is completely suppressed. As the laser wavelength continuesly becomes shorter, the proportion of space-modulated laser required for complete suppression of ARTI decreases. We also find the spatial intensity distribution required to completely suppress ARTI is not sinusoidal corresponding to the initial perturbation. Therefore, we optimize the spatial intensity distribution of the space-modulated laser, and the efficiency of suppressing the ARTI is improved. This may provide a new idea for controlling the evolution of ARTI in future ICF.

The evolution of ablative Rayleigh-Taylor instability (ARTI) was investigated at the Shenguang-II laser facility using X-ray backlight photography. A new re-acceleration phase in the nonlinear bubble evolution was surprisingly observed after the end of the drive laser pulse (coasting phase). The bubble accelerates again during the coasting phase, even surpassing its peak velocity during the drive laser pulse (acceleration phase), resulting in the rapid rupture of the shell. With the radiation-hydrodynamic simulations, we modified Betti’s model [Phys. Rev. Lett. 97, 205002 (2006)] with time-varying r_d and identified that the sustained presence of a vortex pair within the bubble during the coasting phase and the rarefaction waves generated from the rear surface are the primary reason to the bubble re-acceleration. Compared to the bubble evolution during the acceleration phase, the re-acceleration in the coasting phase exhibits a stronger destructiveness to the integrity of the shell, even when the perturbation growth in acceleration phase is quite low. This result may imply new risks to implosion of laser- driven inertial confinement fusion during the coasting phase.

The transport process of a relativistic electron beam (REB) in high density and degenerate DT plasmas holds importance for fast ignition. In the high density plasma, the collisional stopping power dominates REB energy deposition over the Ohmic effect and has traditionally been used to estimate the REB range. Under the assumption, the deflection effect of the self-generated electromagnetic (EB) fields on the trajectory of the REB has long been overlooked for granted.
In the double-cone ignition (DCI) scheme, two DT fuel shells are separately embedded in two head-on gold cones, compressed and accelerated by nanosecond laser pulses. Upon ejection from the cone tips, the high-speed DT plasma jets collide head-on, creating the highly degenerate plasma compared to conventional spherical stagnation. We carefully investigate the self-generated EB fields in the highly degenerate DT plasma. When an REB is injected into an initially degenerate DT plasma, a rapid growth of EB fields ensues. Although the plasma quickly transitions out of the degenerate state, the pre-existing EB fields continuously focusing the REB and subsequently inducing a significant self-organized pinching effect. Through our newly developed hybrid particle-in-cell simulations, we have observed a two-fold enhancement of the heating efficiency of REB than previous intuitive expectation.
This finding provides a promising theoretical framework for exploring the degeneracy effect and the enhanced self-generated EB field in the dense plasma for fast ignition. An experiment to observe this self-organized pinching effect is currently being prepared at the Shenguang II facility for upcoming integrated DCI experiments.

Nuclear fusion has become one of the most promising concepts for future large-scale energy supply. Despite the achievements, there is still a number of challenges that need to be addressed prior to up-scaling to a commercial facility: define the reactor operation mode and configuration, select durable materials, develop effective technologies for T extraction, create the needed support infrastructure....

In this talk we will present the research carried out so far in the Institute of Fusion Nuclear “Guillermo Velarde” related to materials and technology for inertial (laser) fusion reactors operating in the direct drive, dry wall configuration. We will show the limitations of W as plasma facing material [1], the studies carried out on breeder blanket coating materials [2,3] and design [4] as well as, those on final optics materials [5] and technology [6]. We will discuss the need for experimental facilities to test materials under conditions similar to those they will encounter in this type of reactor. We will highlight the importance of developing computational codes that allow us to understand the mechanisms of material degradation.

References
[1] R. Gonzalez-Arrabal, A. Rivera, J.M. Perlado, Limitations for tungsten as plasma facing material in the diverse scenarios of the European inertial confinement fusion facility HiPER: Current status and new approaches, Matt. Radiation at Extremes 5 (2020) 055201.
[2] R. González-Arrabal, E. Carella, F.J. Sánchez, G. de la Cuerda-Velázquez, G. García, J.M. Perlado, T. Hernández, Characterization of the lithium concentration and distribution as a function of depth for alumina coatings after exposure to PbLi, Journal of Nuclear Materials 586 (2023) 154688.
[3] G. de la Cuerda-Velázquez, E. Carella, M. Monclús, Y. Mendez-González, F.J. Sánchez, R. Gonzalez-Arrabal, Deposition of amorphous SiC coatings by RF sputtering and properties optimization for multifunctional barrier applications in the breeding blanket of nuclear fusion reactors, Surface and Coatings Technology 499 (2025) 131897.
[4] A. Fierro, F. Sordo, I.A. Carbajal-Ramos, J.M. Perlado, A. Rivera, Conceptual design of a ceramic breeding blanket for laser fusion power plants with online tunable tritium breeding ratio based on a variable neutron reflector: Remarkable no need of isotopic enrichment, Fusion Engineering and Design 155 (2020) 111648.
[5] D. Garoz, A.R. Páramo, A. Rivera, J.M. Perlado, R. González-Arrabal, Modelling the thermomechanical behaviour of the tungsten first wall in HiPER laser fusion scenarios,
Nucl. Fusion 56 (2016) 126014.
[6] A.R. Páramo, F. Sordo, D. Garoz, B.L. Garrec, J.M. Perlado, A. Rivera, Transmission final lenses in the HiPER laser fusion power plant: system design for temperature control, Nucl. Fusion 54 (2014) 123019.

Nuclear Fusion Reactor designs evolved for decades to solve the engineering problem of the ‘first wall’ [1] which is the ‘vacuum wall’ surrounding the hot fusion plasma. Outside the ‘vacuum wall’ the designs place the ‘neutron blanket’ which is a ‘liquid Lithium blanket’ stopping the fusion neutrons and converting their energy into heat and then electricity, as well as breeding Tritium. The problem is finding vacuum wall materials, for example [1], which can survive long-term the destructive effects of the multi-GW radiation power emitted by the hot fusion plasma in the form of: Neutrons (80% of power), Alpha Particles (20%), X-rays and other energetic ions and electrons – in the case of the front-runner DT burning fusion reactor: 12D + 13T = 24He (3.52MeV) + 10n (14.08MeV).
The proposed solution for laser-driven nuclear-fusion-power-reactors is to bring the ‘neutron blanket’ inside the vacuum of the reactor core such that it surrounds the burning-fusion-plasma, converts the neutron power, breeds Tritium, as well as fully protecting the ‘vacuum wall’ as shown schematically in Fig.1. In this proposed new geometry, the ‘first wall’ becomes the ‘neutron blanket’ and the ‘vacuum wall’ becomes the ‘second wall’ fully protected from radiation by the ‘first wall’. This geometry solves the ‘first wall’ problem: the ‘vacuum wall’, protected from radiation by the new ‘neutron blanket’, can now be manufactured from standard vacuum materials like stainless steel.
For laser-driven fusion-reactors, it is proposed that the reactor core is filled with flowing buffer gas which stops the energetic charged particles (ions) [2.1] emitted by the hot-dense-fusion plasma and converts their power into heat and then electricity, as well as protecting the focusing optics and facing plasma facing panels/devices from coating/damage by plasma ‘debris’ [2.1]. The buffer gas: nature (e.g. He); pressure (e.g. 0.1mBar to 1Bar); and flow-rate around the fusion-plasma; can be optimized [2.1] for particular fusion plasmas. The reactor size [Fig. 1.] is such that the distance between the fusion-plasma and the focusing optics is larger than the stopping-range of the of the plasma debris/ions in the buffer-gas: the gas stopping power is enhanced, and above distance reduced, by the ‘snow-plough effect’ stopping of ions in the buffer gas ionized by the fusion-plasma photons [2.1].
For DD and especially ‘aneutronic’ PB laser-fusion-reactors generating large amounts of X-rays (Bremsstrahlung) it is proposed to install ‘X-ray Panels’ between the fusion plasma and the ‘neutron blanket’ to convert the large fusion generated X-Ray power directly into electric power. Such ‘panels’ could contain sheets of P-I-N X-ray diodes [2.2], be transparent to neutrons and have holes for laser focusing. They should be ‘cheap, fast replaceable consumables’ manufactured by semiconductor industry methods. Buffer gas operation is same as above and will protect the additional ‘panels’ as well.
Propose maximizing the PB fusion-plasma X-ray emission to benefit from direct X-ray conversion to electricity. Also propose exploring solid, non-cryogenic fusion-fuels BNH6, BND6 and BND3T3.

Acknowledgements
ICET thanks his colleagues in the Plasma Physics Group and the UPLiFT Group: Alex Robinson, Robbie Scott, Tony Bell, Raoul Trines, Calum Freeman, Arun Nutter, Robert Paddock and Divya Tank, for discussions in the two UPLiFT seminars where he presented the new proposed solution/geometry of the Fusion Reactor Wall.
References
1. “The ITER Organization made the decision in 2023 to modify the armour material planned for the first wall of the ITER blanket, replacing beryllium with tungsten.”, https://www.iter.org › machine › blanket ; (viewed 20/03/2025)
2. I.C.E. Turcu and J.B. Dance, “X-rays from laser plasmas: Generation and Applications”, book, J Wiley and Sons Ltd (1998) ISBN 0-471-98397-7
2.1. “Towards a Debris-free Plasma X-Ray Source”, Section 7.2, pages 215-223
2.2. “The p-i-n X-Ray Diode”, Section 3.3, pages 104-109

In the first eight rounds of Double-Cone Ignition (DCI) experiments conducted on the SG-II Upgrade facility, a wealth of experimental data has been accumulated [1]. To gain a deeper understanding of the physics and experimental outcomes of the DCI scheme, we selected a set of representative experimental shots and conducted detailed reproduction simulations. The hydrodynamics codes MULTI-2D [2] and OSUKI-3D [3], are employed to model the implosion and burn phases, respectively.
The simulation results show that the key parameters, including density and implosion velocity, are in excellent agreement with the experimental data, validating the reliability of the physical models and numerical methods used. Furthermore, by adopting realistic simulation conditions consistent with the experiments, we revealed the robustness of the DCI scheme under asymmetric laser drive and asymmetric collision conditions. Even when the total laser energy of the two cones differs—leading to varying implosion velocities and off-center collisions—the high-density region of the colliding plasmas still remains a position near the center at the stagnation time, providing favorable conditions for subsequent heating.

References
[1] Zhang J, Wang W M, Yang X H, et al. Double-cone ignition scheme for inertial confinement fusion[J]. Philosophical transactions of the Royal Society A, 2020, 378(2184): 20200015.
[2] Liu Z, Wu F, Zhang Y, et al. Observation of the colliding process of plasma jets in the double-cone ignition scheme using an X-ray streak camera[J]. Physics of Plasmas, 2024, 31(4).
[3] Xu Z, Wu F, Jiang B, et al. Formation of hot spots at end-on pre-compressed isochoric fuels for fast ignition[J]. Nuclear Fusion, 2023, 63(12): 126062.

We investigate the spatial and temporal correlations of hot electron generation in high-intensity laser interaction with massive and thin copper targets under the conditions relevant to inertial confinement
fusion: laser intensity exceeding 10^16 W/cm^2 at a wavelength of 1.34 µm. Using Kα time-resolved imaging, it is found that in the case of massive targets, the hot electron generation follows the laser pulse intensity with a short delay needed for favorable plasma formation. Conversely, a significant delay in the maximum of the X-ray emission compared to the laser pulse intensity profile on the order of more than 100 ps is observed in the case of thin targets. Theoretical analysis and numerical simulations demonstrate that this unexpected significant delay is related to the radiation preheat of the foil and the increase of hot electron lifetime due to their recirculation in a hot expanding plasma. These effects of an increase in the lifetime and population of hot electrons could be important in applications related to laser-driven secondary sources of X-ray radiation and charged particles and in evaluating hot-electron preheat in inertial confinement fusion.

Recent advancements in high-intensity laser-plasma interactions have opened new opportunities for optimizing particle acceleration and secondary radiation sources. Our study focuses on two interconnected aspects of laser-driven acceleration: enhancing MeV photon production and exploring proton-boron fusion using advanced target designs. In the first part, we investigate Direct Laser Acceleration in near-critical density plasmas, optimizing conditions for efficient energy transfer to relativistic electrons. This leads to a significant increase in MeV bremsstrahlung yield, surpassing traditional approaches and improving high-energy photon generation for radiographic applications. The second part explores laser-driven proton acceleration in low-density foams and its application to proton-boron fusion. By employing a confined cylindrical geometry, we aim to maximize proton yield and confinement, enhancing α-particle production. This approach provides valuable insights into laser-driven fusion mechanisms and the development of high-brightness α-particle sources. These experiments, conducted at the PHELIX laser facility, contribute to a deeper understanding of laser energy coupling, particle acceleration, and fusion dynamics, offering pathways for future applications in high-energy-density physics and inertial confinement fusion research.

Liquid targets provide a viable approach for performing high-power laser experiments at high repetition rates. Their intrinsic stability and ability to refresh after each shot make them well-suited for sustained operation. This study focuses on characterizing the thickness and size of liquid sheet targets throughout their operational cycle, starting from atmospheric pressure and progressively pumping down to 6 × 10⁻⁴ mbar.

Key factors influencing liquid sheet stability are investigated, including flow rate oscillations, hydrodynamic instabilities, and the impact of jet alignment and pumping schemes on maintaining laminar flow and minimizing stray jetting inside the chamber. To tackle these challenges, in situ characterization techniques are employed to monitor liquid sheet stability and dimensions in experimental conditions. Diagnostics, such as nanosecond imaging and interferometry, enable real-time assessment of lateral size and thickness fluctuations, ensuring optimal target conditions for laser-driven interactions as shown in Figure 1.

Additionally, the dynamic response of liquid sheet targets to nanosecond laser pulses up to 100 mJ is examined. Time-resolved diagnostics capture the deformation and recovery of the liquid pellicle, demonstrating its ability to sustain consecutive laser shots at 20 Hz and indicating a refresh rate higher than 2 kHz.

These findings offer insights into the behavior of liquid sheets in vacuum and their interaction with high-power lasers. The results have broad implications for laser-driven applications, particularly in generating particle and radiation sources for material testing in fusion research.

The double-cone ignition (DCI) scheme [1] has been proposed as one of the alternative approaches to inertial confinement fusion, based on direct-drive and fast-ignition, in order to reduce the requirement for the driver energy. To evaluate the conical implosion energetics from the laser beams to the plasma flows, a series of experiments have been systematically conducted. The results indicate that 89%~96% of the laser energy was absorbed by the target, with moderate stimulated Raman scatterings [2]. 2%~6% of the laser energy was coupled into the plasma jets ejected from the cone-tips, which was mainly restricted by the mass reductions during the implosions inside the cones. The supersonic dense jets with a Mach number of 4 were obtained, which is favorable for forming a high-density, non-degenerated plasma core after the head-on collisions [3]. These findings show encouraging results in terms of energy transport of the conical implosions in the double-cone ignition scheme.
Our experiments further demonstrated that magnetic fields of hundreds of Tesla enhance fast-electron concentration by about tenfold through field-guided transportation, validated by electron-excited Kα emissions. The result offers a promising path to improve the heating efficiency in fast-electron ignition designs.

[1] J. Zhang, W. Wang, X. Yang, et al., 2020. “Double-cone ignition scheme for inertial confinement fusion,” Phil. Trans. R. Soc. A, 378, 20200015.
[2] Y. Zhang, Z. Zhang, X. Yuan, et al., 2024. “Global scattered-light spectrography for laser absorption and laser–plasma instability studies,” High Power Laser Sci. Eng., 12, e84.
[3] Y. Zhang, Z. Zhang, X. Yuan, et al., 2024. “Efficient energy transport throughout conical implosions,” Phys. Rev. E, 109, 035205.

Electron heat transport plays an important role in Inertial Confinement Fusion, as it significantly affects the efficiency of the capsule compression. The laser energy is absorbed in the low-density corona and transported by the electrons towards the denser ablation front, where it drives compression. Throughout this process, the plasma spans different regimes: energetic electrons from the hot, dilute corona propagate into cooler, denser regions, where collisional effects become important. Various kinetic models describe heat transport in these different regions [Schurtz (2000), Goncharov (2008)]; however, their accuracy can vary as electrons approach the ablation front, depending on the type of ablator and how it influences coupling strength. In this work, the electron thermal conductivity is evaluated across different coupling regimes. For weakly coupled plasmas, Particle-In-Cell (PIC) simulations of protons/electrons are conducted in the local regime using the SMILEI code [Derouillat (2018)]. At higher coupling strengths, NonEquilibrium Molecular Dynamics (NEMD) simulations of the electron One-Component Plasma are conducted using the BinGo code suite [Calisti (2024)], where the Müller-Plathe algorithm is implemented with elongated simulation boxes aligned with the temperature gradient. Comparison of our results with theoretical models [Landau (1936), Spitzer (1956), Lee (1984)] and existing results in the literature [Donkó (2004), Scheiner (2019)] is shown in Fig. 1 for two different elongation factors (xlc). This numerical platform bridges the gap between the kinetic Vlasvo-Landau theory and the N-body classical mechanics. The main perspective is to describe out-of-equilibrium transport for arbitrary plasma coupling parameters.

Steep temperature gradients formed in the coronal region of direct-drive inertial confinement fusion targets produce the conditions necessary for non-local electron transport, and a consequent reduction in heat flow compared to local models. In this work, simulations are carried out using the coupled VFP-hydrodynamics code K2-Gorgon, which can fully capture non-local impacts on electron heat flow in-line with the multiphysics solvers included in Gorgon. This allows detailed benchmarking of heat flow models currently used in ICF design codes, such as flux-limited diffusion and the SNB model.

Simulations were carried out in 1D using a solid plastic (CH) target with incident laser intensities of $\sim {10}^{14}$ W/cm${}^2$, showing substantial differences in temperatures in the conduction region ($\sim 200$ eV) compared to results from flux-limited hydrodynamics. This also leads to a change in shock properties in the CH target. Heat flux is better captured using the SNB model, but differences are still observed. This platform allows for benchmarking models across a range of target geometries and laser parameters relevant to ICF. In targets with gas fills, non-local transport leads to significant preheat, which has the potential to further alter implosion hydrodynamics. Extending this model in 2D will allow the study of magnetic field generation, which is also altered by kinetic effects, and may lead to even more complex modifications to heat flow.

This work was supported by two funding sources:
This work was undertaken as part of UPLiFT (UK Programme of Laser Inertial Fusion Technology for Energy), and is funded by the UK’s Department for Energy Security and Net Zero.

This work was also supported by the EPSRC and First Light Fusion under the AMPLIFI Prosperity Partnership - EP/X025373/1

Laser-plasma instabilities (LPI) are a class of absorption mechanisms that occur when a sufficiently intense laser couples with and amplifies waves in a plasma. LPI are a significant issue for direct drive inertial confinement fusion as they prevent the laser from being collisionally absorbed and supporting compression, instead redirecting the energy into increasing the amplitudes of scattered electromagnetic waves and plasma waves, which accelerate hot electrons. This leads to drive inefficiencies, the risk of implosion asymmetries and fuel preheat as these hot electrons deposit energy across the target ahead of the compression.

We have developed a model designed to run in-line with ray tracing routines that includes the instabilities stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS) and two-plasmon decay (TPD). The instability wave amplitudes are calculated by assuming they have saturated in time by balancing growth rates with saturation mechanisms, which so far include pump depletion, wave dephasing for convective SRS and SBS, and the Langmuir decay instability to limit absolute SRS and TPD. Ray tracing of the scattered light waves allows amplification to be more accurately modelled by considering varying plasma profiles and pump laser fields, while importantly allowing the creation of synthetic scattered light diagnostics.

This talk will present simulations showing how the physics descriptions in the model are tested using data from a planar target experiment on OMEGA.

Magnetization has proven to be an effective strategy to enhance $\alpha$-particle confinement, reduce electron thermal conduction losses, and achieve higher fusion yields compared to conventional inertial confinement fusion implosions. However, accurately characterizing magnetized dense plasmas remains essential for a deeper understanding of the underlying physics. In this work, we present both simulations and experimental measurements of directly-driven magnetized cylindrical implosions conducted at the National Ignition Facility. The targets consisted of cylindrical tubes with a 4 mm outer diameter, enclosed by a 50 $\mu$m-thick plastic shell and filled with 10 atm of ${\text{D}}_2$, along with tracer amounts of Ar and Kr. The implosions were driven by 128-UV laser beams delivering a total of 350 kJ. An initial 16 T magnetic field was applied along the target axis using the MagNIF coil system. The implosion dynamics was investigated using pre- and post-shot 2D extended-MHD simulations performed with GORGON and CHIMERA codes, the latter incorporating 3D ray tracing. Simulations reproduce reasonably the implosion trajectory, assuming a reduced energy coupling of ~70%. Synthetic Ar and Kr K-shell emission spectra were generated throughout the implosion collapse using the NLTE atomics kinetics code ABAKO, coupled with state-of-art Stark-broadened line profiles from the SIMULA code. These results highlight the potential of dual-dopant spectroscopic techniques for diagnosing the compressed core electron temperature and density. However, degraded implosions performance –likely due to the growth of mode-8 instabilities– resulted in a colder-than-expected plasma, preventing the observation of Kr emission lines. Despite this, an independent multizone spectroscopic analysis of the Ar K-shell spectrum yields promising results for inferring core conditions in the magnetized scenario. For upcoming shots in 2025, we aim at increasing the implosion stability by using 2 times larger both shell-thickness and fuel fill pressure.

Foams hold a significant promise for advancing inertial confinement fusion (ICF) by offering several potential benefits, among those the usage of DT-wetted foams in ICF targets. Understanding the behavior of the foam’s microstructure under intense laser irradiation is crucial to unlocking their full potential. However, direct observation of foam microstructure poses significant experimental challenges.
In a novel attempt, we demonstrate the application of X-ray Talbot interferometry to investigate the rapid evolution of laser-accelerated proton heated foam microstructure. Using the dark field signal, which is sensitive to density fluctuations beyond resolution, we effectively discriminate between microstructured and homogenized material states. The unique platform allows to observe the temporal evolution of the foam’s microstructure at various temperature conditions. Obtained results are compared with simulations, showing good agreement.
The results contribute to a better understanding of the behavior of foams in ICF context, making Talbot-interferometry an interesting tool for future studies.

The research on Inertial Confinement Fusion (ICF) requires constant research for identifying new materials. Micro-structured low-density materials, or foams, with a randomly arranged internal structure, have been shown to be able to reduce to some extent the detrimental effect due to hydrodynamic instabilities seeded by non-uniform irradiation, while also increasing the laser absorption efficiency and enhancing the pressure at the shock front. To date, a notable control on the average material parameters has been achieved. However, some parameters of the internal structure, as for example the pore size, cannot be finely tuned to accommodate the experimental needs and gradients of density or pore size cannot still be realized. All these issues can be overcome by using laser 3D printing, with the important benefit of a high reproducibility of the target structure. However, the behavior of such materials under irradiation has not yet been extensively studied.
In this work, we will present the recent results of simulations and experiments about the irradiation of micro-structured 3D-printed materials at high power. We will report about an experimental campaign carried on at the ABC laser facility in the ENEA Centro Ricerche Frascati, with micro-structured materials realized at the Vilnius University Laser Research Center by femtosecond laser additive manufacturing [1]. The samples have been irradiated at intensities from 10¹⁴ W/cm² to about 10¹⁵ W/cm², relevant for ICF. We will also discuss the results of numerical simulations performed with the FLASH code in 3D and run on the ENEA CRESCO High Performance Computing cluster in ENEA Centro Ricerche Portici. The results from the simulations are in good agreement with the experiments and show peculiar features of the behavior of the laser-generated plasma, which can be attributed to the regularity of the structure and to its structural parameters [2].

Acknowledgements
This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. M.M. and A.S. carried out research in the framework of the “Universities’ Excellence Initiative” programme by the Ministry of Education, Science and Sportsof the Republic of Lithuania under the agreement with the Research Council of Lithuania (project No. 374 S-A-UEI-23-6).

References
[1] E. Skliutas et al., Nat. Rev. Methods Primers, in press (2025).
[2] M. Cipriani et al., to be submitted.

The Laser Ion Generation, Handling and Transport (LIGHT) beamline at GSI forms part of the ATHENA distributed facility, which is primarily concerned with the manipulation of phase space in laser-generated ion beams. In recent years, the LIGHT collaboration has achieved the routine generation and focusing of intense 8 MeV proton bunches with a temporal duration shorter than 1 ns (FWHM).
An interesting area of application that exploits the short ion bunch properties of LIGHT is the study of the ion-stopping power of plasmas, a key process in inertial confinement fusion for understanding energy deposition in dense plasmas. The most challenging regime is found when $v_{\text{projectile}}\approx v_{\text{thermal,e}}$, a regime for which ion stopping is difficult to describe and the existing theories show high discrepancies. Since conclusive experimental data is missing in this regime, we plan to conduct experiments on laser-generated plasma probed with ion bunches generated and shaped with the LIGHT Beamline at higher temporal resolution than previously achievable. The high temporal resolution is important because the parameters of laser-generated plasmas are changing on the nanosecond timescale. Therefore, the temporal length of the plasma-probing ion bunches should be as short as possible to reduce the uncertainties caused by the averaging over the fast-changing plasma parameters. To meet this goal, our recent studies have dealt with ions of lower kinetic energies. Laser accelerated carbon ions were transported with two solenoids and focused temporally with LIGHT’s radio frequency cavity. A pulse length of 1.2 ns (FWHM) at an energy of 0.6 MeV/u was achieved. Protons with an energy of 0.6 MeV/u were transported and temporally compressed to a pulse length of 0.8 ns. The temporally compressed and spatially focused ion beam will be used for energy loss measurements. The plasma will be generated by a nanosecond laser (nhelix).

A. Huerta1, C. S. Sanchez2, J.A. Pérez Hernández1, Krish Bhutwala3, M. Ehret4, G. Gatti1, J. Hernandez1, S. Malko3, C. Mendez1, A. Morabito4, D. Tofiño1, and L. Volpe1,2

1Centro de Laseres Pulsados (CLPU), Parque Cientifico, 37185 Salamanca, Spain
2ETSI Aeronáutica y del Espacio, Universidad Politécnica de Madrid, 28040 Madrid, Spain
3Princeton Plasma Physics Laboratory, 100 Stellarator Road, Princeton, NJ 08536, USA
4ELI Beamlines Facility, The Extreme Light Infrastructure ERIC, 25241 Dolní Bˇrežany, Czech Republic.

Transporting ultra short laser driven ion beams is crucial for studying their stopping power in Extreme states of matter like for example the Warm Dense Matter (WDM). From theoretical point of view the region close to the Bragg peak where the proton velocity is comparable to the WDM thermal electron velocity is relevant to discriminate different models which provide consistent differences in that region. In order to investigate the Bragg peak region [1] thin targets (1 um) are required, and this imply a reduced stagnation time (< 100 ps). To perform isochore measurement the duration of the ion probe must be maintained shorter than the stagnation time which imply a challenge, especially for low energy proton beams ~ hundreds of keV that spread in time significantly (i.e 100 keV can experience an increase in temporal length at an approximate rate of 70 ps per centimeter of transport).

An isochrone magnetic selector has been designed as reported in ref [2] to reduce the proton pulse time spread during the transport and a first experimental campaign has been performed in the VEGA 3 PW-class system at the Pulsed laser center in Salamanca to characterize the energy spectrum and pulse duration of the laser driven proton beams. The energy spectrum was measured by using the High-resolution ion spectrometer developed @ CLPU [3] while the proton pulse duration was estimated by using diamond detectors in time-of-Flight mode.

Here we present the first experimental results by showing energy spectrum and pulse duration of the selected proton beam together with preliminary estimation of the best parameters to approach Bragg peak conditions.

References
[1] S Malko, et al and L. Volpe, “Proton stopping measurements at low velocity in warm dense carbon”
Nature Communications 13 (1), 2893
[2] JI Apiñaniz, et al and L. Volpe, “A quasi-monoenergetic short time duration compact proton source for probing high energy density states of matter”, Scientific Reports 11 (1), 6881
[3] L Volpe, et al, “A Platform for Ultra-Fast Proton Probing of Matter in Extreme Conditions” Sensors 24 (16), 5254

Corresponding author L. Volpe l.volpe@upm.es

Near-critical density (NCD) targets present a promising alternative to over-dense foil targets for high repetition rate, debris-free laser-driven ion sources. State-of-the-art Particle-In-Cell (PIC) simulations demonstrate accelerated ions with energies up to hundreds of MeV in the NCD regime, yet experimental demonstrations remain scarce due to the need for precise control over target profile characteristics as peak density and density gradients.
We report the first experimental validation of our simulations1 demonstrating a novel method of optical shaping under-dense gaseous profiles into NCD targets. Dual, intersecting laser-generated blast waves compress the gas upon shock fronts collision, forming steep density gradient slabs of a few microns scale length. The compression of the target is maintained over several ns, mitigating laser synchronization issues.
3D HydroDynamic (HD) simulations are used to optimize the target shaping, while incorporating the effects of the inherent Amplified Spontaneous Emission of the accelerating laser system. An ‘in-house’ developed, synthetic optical probing algorithm provides accurate matching of simulations to the experimental results.
Ion acceleration experiments are conducted using the 45 TW, fs laser system Zeus, hosted at the Institute of Plasma Physics and Lasers (IPPL)2. Measurements of multi-MeV ions energy spectra and high-dose electron emission are presented. Furthermore, the super-intense laser - NCD profile interaction is modelled by 3D PIC simulations. The simulations reveal the generation of multi kT, azimuthal magnetic fields, strongly suggesting that Magnetic Vortex Acceleration is the underlying acceleration mechanism.

Acknowledgments
This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion) and the Hellenic National Program of Controlled Thermonuclear Fusion. Views and opinions expressed are however those of the author only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. We acknowledge the support with computational time granted by the Greek Research & Technology Network (GRNET) in the National HPC facility ARIS-under project ID pr016025-LaMPIOS IIΙ.
References
1. Tazes, I., et al. Sci. Rep. (2024). DOI: 10.1038/s41598-024-54475-1
2. Clark, E. L., et al. High Power Laser Sci. Eng., (2021), pp. 1–28., DOI: 10.1017/hpl.2021.38

Compared with DT thermal nuclear fusion scheme, proton-boron fusion attracts less attention because it requires higher temperature for the maximum cross section and it is difficult to realize the energy gain over the bremsstrahlung loss. However, high power lasers open the path to fusion under non-equilibrium condition like fast ignition scenario but the fuel is boron. In this way, the protons will not only serve as the heating source but directly induce nuclear reaction. In this talk, we will introduce our recent results concerning the intense particle beam generation as well as beam-target nuclear reaction study based on high power lasers as follows.
(1)We experimentally generated brilliant electron beams and gamma rays through picosecond-laser-NCD (near critical density) plasma interactions. With the same laser, the electron beam energy and temperature are enhanced by one order compared with foil case. The gamma rays are enhanced by two orders if a high-Z converter are used.
(2)We experimentally studied the pB nuclear reactions both with pitcher-catcher and in-target scheme. In the pitcher-catcher scheme, we experimentally created CHOB plasma through heating a foam target with nanosecond-laser-induced hohlraum radiation in the soft x-ray regime. Intense proton beam was generated through target normal sheath acceleration mechansim based on high-power picosecond laser. In this way, we can have very good knowledge about the beam and target parameters. The preliminary results show that the reaction product yield is enhanced in plasmas compared with cold matter, and the yield increases with beam intensity non-linearly. In the in-target scheme, we focused the picosecond laser into the porous-structured CHOB target. In comparison with laser-foil interactions, higher number of protons are observed along the target normal direction as well as in directions perpendicularly to the laser propagation direction. Higher-yield of pB nuclear reaction is corresponding obtained. This provides a perspective way for laser-driven pB nuclear reaction studies and compact alpha sources.
(3)We conducted 12C(e/γ, p)11B reaction measurement to discriminate the mechanism for the p11B nuclear reaction enhancement. The electrons and gamma rays, that are usually generated simultaneously with protons, induced very little proton and boron element in the target, and had negligible influence on the proton boron nuclear reaction enhancement.