Evaluation of Rosenbaum's proposal for locally increasing the effective vertical emittance of the APS beam.

摘要

At the APS Retreat in May 2002, G. Rosenbaum proposed a method for increasing the effective vertical emittance of the APS beam. His proposal, illustrated in Figure 1, is to use a rapidly-modulated four-magnet vertical position bump in a single straight section. The proposed modulation frequency is a 10-kHz triangle wave, with a kick angle of 0.65 mrad. There are several aspects of this proposal that may be problematical: (1) The high modulation frequency will require the use of a ceramic chamber with a thin conductive coating, similar to what is used for the injection kicker magnets. This is not necessarily a problem, but the following aspects need to be examined: (a) The chamber coating needs to be specified correctly to ensure that the beam motion reflects the desired triangle-wave pattern. (b) The effect of the eddy currents in the chamber on the multipole content of the magnetic field needs to be computed, to ensure that the system does not have undesirable effects on the beam. (2) The magnets and their chambers will require careful matching in order to ensure that the beam is not disturbed outside of the bump. We know from experience with the APS kickers that this can be difficult. These issues are examined in the remainder of this note. The magnet and power supply designs are beyond our scope. We simply point out that these will not be conventional magnets or power supplies. The magnets will almost certainly need to be of ferrite construction, similar to the injection kickers. The power supplies will be unique and unlike anything else in the APS ring.