SPARC: Electron Targets / Cooler
The task of the SPARC working group "Electron Targets/Cooler" is to develop and leverage the techniques and the equiment to study electron ion collisions at GSI's and FAIR's heavy ion storage rings.
Electron Ion Collisions
Collisions between free electrons and ions belong to the most fundamental process in atomic physics. Within the SPARC collaboration, primarily electron collisions with stable heavy highly charged ions and with artificially synthesized radioisotopes are envisaged. In a storage ring, the circulating ions repeatedly interact with the target electrons thus allowing investigations of low-intensity projectiles and/or of processes with low cross sections to be carried out. In addition, the storage ring environment provides very clean experimental conditions owing to phase-space cooling and dedicated control of the isotope and charge state of the ion.
In the original plans towards the Facility for Antiproton and Ion research (FAIR) the New experimental Storage Ring (NESR) was intended to be the major experimental site for the investigation of electron-ion collisions. Within the modularized start version of FAIR, the NESR is postponed to 2025 or even later. Hence, it was decided that the SPARC electron target working group focusses on electron-ion collisions at the storage rings ESR and in particular at its upcoming companion CRYRING@ESR.
At present, at ESR and at CRYRING@ESR mainly two classes of experiments are planned:
- Photon or electron spectroscopy produced in collisions between free target electrons and stored ions.
- Precision spectroscopy and lifetime studies utilizing energy-sharp resonant features in the electron-ion cross section (‘collisions spectroscopy’). More details about collision spectroscopy can be found here. With the same approach cross sections and resonance strengths are determined on an absolute scale, thus providing an in-depth understanding of electron-ion collisions and their dynamical aspects.
Three main experimental installations will be used to reach these goals:
- High-energy electron-ion collisions with a stochastically cooled ion beam: for high collision energies studies will performed in the ESR with a permanently stochastically cooled ion beam using the ESR cooler as free-electron target.
- High-resolution merged-beams collision spectroscopy at CRYRING@ESR.
- At CRYRING@ESR a dedicatedfree-electron target that operates in transverse collision geometry:the setup will be optimized for electron and photon spectroscopy.