Beam Loading Effect and Adiabatic Capture in SIS-18 at GSI

For the projected Facility for Antiproton and Ion Research (FAIR) at GSI the upgraded, existing synchrotron SIS-18 will be used as an injector. The increased beam intensity in the upgraded SIS-18 is expected to cause additional collective effects, leading to beam loss or beam quality degradation.

Beam interaction with radio frequency (rf) cavity, resulting in beam loading effect, is an important consideration in the design and operation of high-intensity circular particle accelerators. The steady state and transient perturbation of the rf cavity system by the circulating beam can be harmful to the beam and limit the accelerator performance. Steady state beam loading effect is observed in SIS-18 with single and double rf operations. The supportive simulation and theoretical study is done, to extrapolate the results for the upgraded SIS-18.

In SIS-18 the coasting beam, i.e. an unbunched dc beam, is captured by using the rf cavities. RF capture is one of the potential sources for longitudinal beam quality degradation at high intensities. Therefore this part of the SIS-18 machine cycle requires dedicated studies. The rf voltage ramping time and the initial voltage amplitude are important parameters to be controlled. This study of longitudinal beam dynamics is helpful to determine the optimum type of voltage ramp, in terms of beam quality and total cycle time. A theoretical study has been made in this direction, supported by simulations. In line with that the experiments have been performed in SIS-18.