HERA electron-beam lifetime disruption machine studies and observations

Extensive machine studies of the electron beam lifetime problem in HERA were performed in Dec 1995 at energies ranging from ?? GeV to ???? GeV and at currents up to ?? mA. Transient and persistent rate increases observed in 214 electron beam loss monitors around the machine and in background and electron detectors at the ZEUS, HER- MES and H1 experiments coincided with transient and per- sistent electron beam lifetime disruptions. The observa- tions were consistent with the passage through the electron beam of dozens of disrupting targets (dust particles) per minute, whereby many permanent lifetime disruptions and local electron loss rate increases (stationary target trappings in quadrupoles) could be observed per hour at high current and energy. Detectors indicated frequent longitudinal mo- ?? tion of transient disrupting targets at speed ? ?? m s at ?? GeV along arc regions, the targets apparently being frequently lost in straight sections. The time evolution of electron loss monitor rates around the ring illustrates clearly the passage of targets through the beam, the trapping of tar- gets in particular quadrupoles, and the successful removal of many disrupting targets by strong repeated beam kicking and high-frequency beam kicking.

The integrated ion pump system was again implicated as the disruption culprit. Regions most prone to disrup- tion were identified and integrated ion pumps there were replaced with trial Non-Evaporative-Getter (NEG) pumps. Preliminary results from NEG pump trial machine studies from 24/05/96 to 08/06/96 are presented.