LBNL, Berkeley, California
CERN, Geneva
SLAC, Menlo Park, California
Clouds of low energy electrons in the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation of these machines at high currents. Because of the size of these accelerators, it is difficult to probe the low energy electron clouds over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave which is independently excited and transmitted over a section of the accelerator. We infer the absolute phase shift with relatively high accuracy from the phase modulation of the transmission due to the modulation of the electron cloud density from a gap in the positively charged beam. We have used this technique for the first time to measure the average electron cloud density over a 50 m straight section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center. We have also measured the variation of the density by using low field solenoid magnets to control the electrons.
LBNL, Berkeley, California
The superconducting, electron cyclotron resonance (ECR) ion source VENUS has been designed for the dual roles of ion injector for the 88-Inch Cyclotron at LBNL and prototype high current, medium charge state injector for the driver linac of a proposed U.S. radioactive ion beam facility. Ion beam extraction and transport from an ECR is complicated as the plasma-confining solenoidal and sextupolar fields produce beams lacking axial symmetry, these beams are composed of multiple charge states with varied distributions at extraction, and the beams undergo species-dependent rotation while leaving the confining magnetic fields. We are developing an accurate, adaptable simulation model to aid in both understanding the current VENUS system and optimizing the source and transport system for the future facility. VENUS has been outfitted with various beam diagnostics such as viewing screens, a multi-wire harp, emittance scanners, and energy analyzers, and these play an essential role in correlating simulation with experiment. We will describe in detail the diagnostics employed in the VENUS beam line. Measurements with these devices will be presented and compared with ion beam simulations.