Speaker
Description
The Penning ion source serving the ISIS Pulsed SpallationNeutron and Muon facility routinely delivers55 mAbeamof negative hydrogen ions (H−) in250μspulses at50 Hzrep-etition rate. The Front End Test Stand (FETS) specificationsrequire60 mA,2 ms, pulses at50 Hz. Extending the ionsource discharge pulse length to2.2 mswill need overcomethe observed beam current droop caused by thermal tran-sients in long pulse operation. Recent experiments at25 Hzhave demonstrated square60 mAbeam pulses up to1.2 mswith the permanent magnet version of the ISIS source and100 mApulses up to1.65 mswith the same source equippedwith a double-width extraction slit. Droop was compen-sated by ramping up the discharge current during the beampulse. The physical phenomena underlying the droop and itscountermeasures are discussed, and further technical devel-opments that are necessary to reach the FETS specificationsare described. In addition, various experimental shapes ofthe ion source discharge pulses and H−beam pulses wereachieved by controlling the ion source discharge currentand accelerated through the ISIS70 MeVlinac. The tech-nique allows almost arbitrary shaping of the H−beam pulsesfor injection studies into the800 MeVrapid cycling protonsynchrotron
