06/26/97 Update

PEP-II Update June 26

PEP-II Update June 26 (Thursday)

The HER team under Uli Wienands with Yunhai Cai, Martin Donald, Mike Sullivan, Artem Kulikov, Mike Zisman, Alexander Zholents, Jim Turner and many others, the RF group under Matt Allen, Heinz Schwarz, Bob Rimmer and Paul Corredoura with Jim Judkins, Rich Tighe, Stephanie Allison and many others, and the injection group under Dave Schultz with Rich Iverson, John Sheppard, Ted Fieguth, Marc Ross and friends have pushed the HER to new levels.

The polarities of the ring sextupoles have been fixed and the chromaticities were set to slightly positive values. The beam lifetime did not change and is about 3 hours at low currents at 8.5 GeV.

We are now in a process of increasing the number of bunches. Several filling patterns have been tried including 7, 14, 17, and 24 equally spaced bunches as well as several shorter bunch trains. The best filling at present is with 17 equally spaced bunches. Injection is at 1 Hz with about 0.1 mA per injection cycle. We're injecting slowly so not to exceed our approximate current limit of about 50 to 100 mA due to a dozen or so vacuum chambers which do not yet have water cooling.

This morning the current reached 50 mA in these 17 bunches. Injection is not as good with the other fill patterns. The vacuum pressure in the ring arcs has gone up about a factor of 10 and the beam lifetime at 40 mA is about one hour. The peak bunch charge is about 9 mA which is an order of magnitude above the PEP-II design current per bunch of 0.6 mA.

At high currents the filling of the 17 bunches is not uniform. With injection up to 17 mA all bunches have equal charges. Above that level the pattern becomes a sawtooth with about 6 bunches (adjacent) of high charge and the rest at lower charge. The longitudinal feedback (bunch by bunch) has been tried but did not affect the result. A form of multibunch instability is likely but not yet proven.

Our near term task is to turnon the transverse feedback system and to increase the number of bunches with about 1 mA each.

The next update will come next week when our run ends July 1st.

Regards, John

Suggestions to: John Seeman

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