CRYRING@ESR Detectors Workshop

The expected performance of the Cryring will provide the possibility to investigate direct reactions with cooled and stored exotic beams in inverse kinematics. In particular, the energy regime of the Cryring will perfectly fit to the demands for the investigation of one- or few-nucleon transfer reactions. A new and innovative detector setup, including UHV compatible Si detectors, located around and downstream from the internal target area, was recently designed, constructed, and successfully applied for the investigation of in-ring reactions with exotic beams at the ESR. The design and performance of this experimental setup will be displayed, and potential applications at the Cryring will be discussed

The combination of a gas jet and bare ions stored at low energy as provided by the CRYRING allows to study e.g. proton or alpha capture reactions in the astrophysically relevant energy window. For this purpose a versatile diagnosis chamber is currently beeing designed that allows the detection of reaction products on various tracks after the dipole downstream the gas target. The current status of the chamber as well as related detector manipulators and potential detector choices will be presented and compared to the already existing setup at the ESR.

First experimental beamtimes have been performed at the Cryogenic Storage Ring (CSR) of the Max Planck Institute for Nuclear Physics (MPIK) in 2015. The CSR is a fully electrostatic machine operating at ~6 K temperature and at typical ion energies of ~100...0.5 keV/u. The experimental programme focuses on atomic and molecular physics. Product particle detection is challenged by, both, the low temperature of the CSR beam pipe and the low particle energies. The talk presents a movable, single-particle counting detector that has been developed at MPIK. The device is compatible with the cryogenic environment of CSR and suitable for lowest ion energies. It was used productively in the initial 2015 beamtimes and now serves as prototype for several further CSR detectors of its kind. The talk summarises the expertise gathered during operation of the device, and closes with a brief overview of different, but related, detector equipment that is being prepared for upcoming CSR beamtimes.

The FISIC experiment ("Fast Ion-Slow Ion Collisions") constitutes a novel attempt to better understand the ion-ion interactions occurring in the so-called intermediate collision regime, where the speed of the active electrons is comparable to the relative target-projectile speed. Under these conditions, the cross sections of the involved charge-exchange processes are largest, and of similar magnitude across multiple interaction mechanisms. Previous attempts to gain insights into the intermediate regime have been hindered by both the intricate theoretical treatment as well as the challenging task of separating different interaction paths in experiment. The FISIC experiment, planning to use intense ion beams at the SPIRAL2 and FAIR facilities, aims to shed some light on the details of the interactions taking place. A major challenge of this experiment is the development of ion detectors that can sustain the expected count rates of some MHz and ion energies ranging from sub-MeV/u to 15 MeV/u. Conventional sensors, such as devices based on semiconductors or plastic scintillators, are unlikely to be able to cope with the radiation damage incurred. One of the solutions investigated utilizes YAP:Ce crystal scintillators, a material which has been successfully employed for ion detection in earlier investigations. After a general overview of the FISIC project, this contribution will detail first investigations into the feasibility of a scintillator sensor system.

The low energy storage ring CRYRING is currently being set up as the first storage ring of the upcoming accelerator facility FAIR at GSI. CRYRING features an electron cooler to cool stored ions and thus achieve a low momentum spread of the beam. To determine the velocity of the ions a precise knowledge of the acceleration voltage of the electron cooler is essential. In earlier measurements of hyperfine transitions in hydrogen- and lithiumlike ions at the Experimental Storage Ring (ESR), the limiting uncertainty was the voltage measurement of the electron cooler. That uncertainty could be removed by an in-situ precision measurement of the cooler voltage using a precision high voltage divider provided by PTB on a temporary basis. Since commercially available high-voltage dividers do not offer the desired precision and stability for use at CRYRING, we construct a high-precision divider for voltages up to 35 kV which will be similar to the ultrahigh-precision voltage dividers which have been constructed in Münster in cooperation with PTB for use at the KATRIN experiment. The precision of the divider will be in the low ppm range and will, if other sources of systematic uncertainties like e.g. space charge effects are under control, allow for measurement uncertainties in the <10 E-5 region. The divider concept, characterization measurements of the precision parts and the status of the project will be presented. This work is supported by BMBF under contract number 05P15PMFAA.

A dedicated laser-induced fluorescence detection region needs to be impleneted into the first part of the experimental section of CRYRING (section 9). Additional supporting infrastructure is also needed to facilitate stable and safe use of lasers in and around CRYRING. It includes a laser laboratory, laser beam transfer tubes as well as coupling platforms with optics around the ring. The preliminary design and positioning of these components will be presented and open for discussion or coordination with other experiments.

CRYRING offers the possibility to perform high precision laser spectroscopy experiments on a range of highly charged heavy ions. The wavelengths of fluorescence photons emitted in these experiments range from the UV (e.g. transitions in singly charged magnesium and beryllium ions at 280 nm and 313 nm, respectively) to the near infrared (e.g. in measurements of dielectric recombination in singly charged calcium ions at 854 nm and 866 nm). For these laser spectroscopy experiments a general purpose optical photon detection system is needed, which should efficiently collect fluorescence photons emitted along the ion beam while suppressing background photons produced by excited rest gas molecules in the beam pipe volume. In order to achieve this, we use elliptical mirrors to reflect photons towards the viewport windows and a compound parabolic concentrator, to further guide photons under specific incident angles onto PMTs. Different options are used for the UV- and infrared photons and are analyzed with a Monte Carlo simulation. The resulting optimized detector design and expected efficiency will be presented. The project is supported by BMBF under contract number 05P15PMFAA.

CRYRING offers the possibility to perform laser spectroscopy experiments in the extreme ultraviolet (XUV) region with highly charged ions. Therefore a table-top, high repetition rate, and high photon flux XUV source is needed. The talk presents recent developments of such a tailored XUV source, based on high harmonic generation of a high repetition rate femtosecond fiber laser system, as well as the planned implementation at the CRYING.