Diploma Thesis of Christoph Steier

I finished my diploma thesis on beam instabilities induced by ions in November 1995.

published as: BONN-IB-95-40

Title:
Theoretische und experimentelle Untersuchungen zu Vielteilcheneffekten bei der Elektronen-Stretcher-Anlage ELSA

Abstract:
In electron storage rings the circulating electrons interact with the residual gas and ionize molecules producing positive ions. The ions can be trapped by the electrical field of the electron beam. Trapped ions have many deterious effects on the electron beam, for example tune shift, emittance blow up and transverse instabilities. These effects limit the performance of the 3.5 GeV Electron Stretcher Accelerator ELSA for high beam currents, especially in storagemode operation. To understand the conditions which favour ion trapping the dynamics of the ion motion has been investigated by simulations. Moreover several methods to minimize the impact of ions on the beam quality have been tested and implemented into routine operation. Important beam parameters like lifetime and emittance have been improved up to a factor of three for high beam currents above 200 mA. Transverse coherent instabilities between the electron beam and the ion cloud could be successfully suppressed.

Talks/Conference Contibutions about Ion Trapping:

• You can get the transparencies of a talk on 'Performance and Future Developments at ELSA' I gave in September 1996 at the 'workshop on electromagnetic interactions' in Bosen (Saar) organized by the University of Mainz. (use swap landscape in ghostview.)
• In May 1997 I was at the PAC 1997 in Vancouver and presented a poster mainly about simulations concerning the 'Correction of Depolarizing Resonances in ELSA' there. Some results on ion induced instabilities were also given.