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.
PSI, Villigen
DESY, Hamburg
Currently, a prototype fast intra bunch train feedback system is under development which is to be tested at FLASH. For pickups as well as kickers, stripline devices have been developed. The new pickup is based on the earlier designs used in the transfer lines of the swiss light source as well as in the proton cyclotron PROSCAN at PSI; in particular, the stripline electrode output coupling is intentionally mismatched in order to increase the shunt impedance seen by the beam. Two versions have been designed for a center frequency of 1.65 GHz and a loaded Q of 35. Prototypes have been fabricated and built into FLASH. The stripline kicker consists of four main elements (all in-vacuum): two stripline electrodes fabricated from extruded aluminum and two metallic ground planes, held in place by ceramic spacers. The latter reduce the mutual inductance between the electrodes and optimize the RF match for asymmetries in the RF feed. Prototypes have been built, measured in the lab, and are now in the process of being inserted into FLASH.
KEK, Ibaraki
SLAC, Menlo Park, California
Dimtel, San Jose
A bunch-by-bunch feedback system has been developed to suppress longitudinal coupled-bunch instabilities at the KEK-PF. A generalpurpose signal processor, called iGp, has been developed by a collaboration among KEK, SLAC and INFN-LNF. A longitudinal kicker based on the DAΦNE-type over-damped cavity was designed and installed in the ring. The whole feedback loop was closed at the end of June 2007. The longitudinal dipole-mode instabilities are successfully suppressed up to 430 mA. The performance and the details of the system will be presented in this paper.
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.