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Electron-Ion Collision Studies at the ESR Electron Cooler with a Stochastically Cooled Ion Beam

At the ESR, in addition to electron cooling the ion beam can also be cooled be means of stochastic cooling at a fixed ion energy of about 400 MeV/u. This alternative cooling technique allows cooling and measurement to be decoupled from one another. For electron-ion collision studies the ion beam is cooled by stochastic cooling only. The electron cooler is exempted from its cooling tasks an serves as a free-electron target. While this approach does not deliver the outstanding resolution at low collision energies that is achieved at the CRYRING electron cooler it features several other outstanding capabilities:

  • Collision energies of 200 keV in the center-of-mass frame.
  • Virtually no ion beam loss due to the cooling process.
  • An experimental duty cycle close to one, since no intermittent electron cooling between measurement steps needs to be performed.

Using this new technique, dielectronic recombination of one-electron uranium (U91+) could be studied with a resolution close to the natural linewidth. However, in these first studies the ion beam could only be stochastically pre-cooled and not permanently cooled due to particle detector positions not well suited for a stochastically cooled beam leading to a deterioration of the energy resolution.

In order to fully utilize the potential of this new approach a new detector actuator was installed in the first dipole magnet behind the electron cooler. This position is ideally suited for collision studies at the ESR cooler with a stochastically cooled beam. It can be expected that the resolution no becomes sufficient to study line widths and even line shapes of Δn >= 1 dielectronic recombination processes such as KLL-DR of U91+ or U90+. Furthermore, electron-impact ionization of U91+ U90+ or U89+ comes into reach or even more exotic process as the long sought-after process of nuclear excitation by electron capture (NEEC), i.e., the time-inverse to internal conversion.

https://www.gsi.de/fileadmin/user_upload/ESR_cooler.jpg
ESR electron cooler
ESR electron cooler

A New Detector Manipulator for the ESR

In order to fully utilize the potential of this new approach a new detector actuator was installed in the first dipole magnet behind the electron cooler. This position is ideally suited for collision studies at the ESR cooler with a stochastically cooled beam. It can be expected that the resolution no becomes sufficient to study line widths and even line shapes of Δn >= 1 dielectronic recombination processes such as KLL-DR of U91+ or U90+. Furthermore, electron-impact ionization of U91+ U90+ or U89+ comes into reach or even more exotic process as the long sought-after process of nuclear excitation by electron capture (NEEC), i.e., the time-inverse to internal conversion.

https://www.gsi.de/fileadmin/user_upload/Detector-manipulator.jpg