University of Heidelberg

Research

Photoelectric Effect

We study Photoelectric Effect in the regime of hard x rays and strong Coulomb fields via its time-reverse process of Radiative Recombination (RR). The latter is one of the dominant processes in collisions of electrons with ions. It is also strongly pronounced in hot plasmas. To investigate properties of this process we do experiments at the heavy ion storage ring ESR in GSI Darmstadt.

Resonant Recombination

Resonant Photorecombination is one of the dominant recombination mechanisms in hot plasmas. It strongly affects the ion charge ballance in the plasma and the spectrum of the plasma x rays. In experiments at Electron Beam Ion Trap (EBIT) in Max-Planck Institute for Nuclear Physics in Heidelberg we study alignment and polarization properties of the resonant recombination including exotic channels such as trielectronic and quadroelectronic recombination.

Bremsstrahlung

Radiation emitted by relativistic electrons moving in the field of a heavy nucleus can serve as a sensitive probe to the electron dynamics. A particular emphasis of the current experimental studies is given to the electron spin effects which strongly influence the polarization of the emitted bremsstrahlung photons. Experiments in this direction are performed using the polarized electron beam of SDALINAC accelerator of Technische Universitšt Darmstadt and Mainzer Microtron MAMI.

Plasma Polarization Diagnostics

Many hot plasmas are anisotropic. Those include fusion plasmas at tokamaks and stellarators, laser-produced plasmas as well as astrophysical plasmas in active galactic nuclei and solar flares. We develop techniques and instruments for diagnostics of anisotropies of hot laboratory plasmas via x-ray polarimetry. We have tested them using an electron cyclotron resonance ion source in Laboratoire Kastler Brossel in Paris.

Advanced X-Ray Detectors

We develop technologies and instruments for x-ray polarimetry and imaging. Our polarimetry techniques cover the energy range from 10 keV up to several MeV, and we work to further extend these limits down to 1 keV. In the energy range of 100 keV we improved the polarization angle sensitivity down to 0.3 deg. We also develop techniques for circular polarimetry of gamma rays, in particular the ones which can be applied for astrophysical observations.