06/23/97 Update

PEP-II Update June 23

PEP-II Update June 23

Since the last update we have been busy with HER activities. The HER is at 8.5 GeV with the IR insertion quadrupoles still at half strength. The linac is being shared with the SLC program.

By Friday June 20 we had obtained a lifetime of 5 minutes. Over the weekend careful tuning of the beam position in the x and y apertures in the interaction region with three corrector bumps gave way to a slowing increasing lifetime. The lifetime reached 35 minutes (1/e) by 11 pm Saturday June 21. We then moved onto testing instrumentation: the DCCT and bunch-by-bunch current monitors, the tune monitors, and a look at beam signals in the the longitudinal and transverse feedback systems. The transverse system was used to kick the beam to make tune measurements. These transverse electrodes could easily kick the beam out of the HER as driven by the sweeping of the spectrum analyzer if turned up too high.

On Sunday the RF frequency was unlocked from the linac and the vertical chromaticity was measured. The chromaticity was -66 units which was twice the expected natural (uncorrected) value of about -34 units. Increasing the SD sextupole strengths made the chromaticity more negative. When the sextupoles were all turned off, the natural chromaticity was measured and, amazingly, a beam lifetime of 3 hours resulted! (In the end, we had carefully and systematically wired all sextupoles backwards. Oops!) However, the good news is that the HER dynamic aperture seems to be quite large.

Today the sextupoles are being rewired and, after a day of positron extraction studies, the HER studies will start again.

All for now and congratulations to everyone.

Cheers, John

Suggestions to: John Seeman

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