Plasmaphysik Seminar

Ion stopping measurements near the Bragg peak in laser-induced plasmas

by Dr. Witold Cayzac (École Normale Supérieure Paris-Saclay / CEA-DAM Île-de-France)

Tuesday, June 19, 2018 from to (Europe/Berlin)
at GSI Darmstadt ( Seminarraum Theorie )
Ion stopping in plasmas is still poorly understood for low projectile velocities, where the beamplasma interaction takes place around and below the stopping-power maximum (Bragg peak). Large uncertainties are reported on the theoretical stopping-power modelling [1,2], and very few measurements are available. However, a fine knowledge of the stopping power in this parameter range is essential in the frame of ICF. In particular, the ignition threshold of ICF capsules depends on the stopping-power modelling [3].
Here, we report two experiments using low-energy accelerator-produced ions probing a laserinduced carbon plasma for measuring the ion stopping close to the Bragg peak. For the aimed plasma temperatures of 100-200 eV and electron densities of 1020-1021 cm-3, stopping-power differences of 20-30% are predicted using beam energies around 0.5 MeV/u [2]. The energy-loss measurements are performed by time of flight using specifically developed diamond detectors on chemical-vapour-deposition (CVD) basis.
Firstly, the results of an experiment performed at GSI on the UNILAC accelerator and the PHELIX laser facilities are presented. A fully ionized carbon plasma was probed with nitrogen projectile ions decelerated through a carbon degrader foil. The data provide a discriminating test of stoppingpower theories, showing that only the stopping theories including close collisions (T-Matrix, BPS) are consistent with the measurements [4].
Secondly, we present the data of the first campaign obtained on a new experiment at CEA-DIF that combined the 4MV accelerator and the GCLT laser system. In this campaign, alpha-particles at a 0.5 MeV/u energy interacted with a partially ionized carbon plasma with temperatures of up to 100 eV. The plasma characterization is based on the measurement of the XUV emission using two distinct spectrometers. The energy loss has been measured with a novel CVD diamond detector with
coplanar interdigitated electrodes for an enhanced sensitivity to low-energy ions [5]. This detector delivered first promising results and is going to be further optimized in the future. The obtained energy-loss results are presented and discussed.

[1] D. O. Gericke and M. Schlanges, Phys. Rev. E 67, 037401 (2003)
[2] W. Cayzac et al., Phys. Rev. E 92, 053109 (2015)
[3] M. Temporal et al., Eur. Phys. J. D 17, 132 (2017)
[4] W. Cayzac et al., Nat. Commun. 8, 15693 (2017)
[5] W. Cayzac et al., Rev. Sci. Instrum. 89, 053301 (2018)