11/28/98 Update
11/28/98 Update
PEP-II has had beam continuously for the past four weeks. We have evolved to a schedule where the individual rings commission six days per week and we collide the seventh day (Tuesdays). We have useful beam about 95% of the time.
The Low Energy Ring (LER) has concentrated on orbit control, lifetime issues, and lattice correction. The orbit has now been steered to about 1 mm rms in the vertical plane and 1.8 mm in the horizontal. The betas in the interaction region quadrupoles have been measured and the vertical corrected. The vertical beta* is now 1.5 cm. The chromaticities are in the range of +1 to +3 units. The emittance wiggler magnets are now turned on continuously. The x-y coupling has been reduced to below 0.001 (minimum tune separation). The beam lifetime at 1 mA remains at about 90 minutes and is 20 minutes at 100 mA. Significant vacuum scrubbing has occurred. The LER now has over 7 Amp-hr of integrated positron beam. After adding cooling to a temporary vacuum chamber, the LER has reached a beam current of 266 mA in 291 bunches uniformly spaced. (Rumor has it that 274 mA was seen but not recorded.) The transverse feedback system has been turned on and is fully working.
The High Energy Ring (HER) has stored up to 217 mA in 87 bunches or '97-10' as it is referred to (i.e. 97 uniformly spaced bunches with a 10 bunch ion gap.) The HER has a low threshold to transverse instability (cured by feedback). The source of the instability has received a great deal of attention and the threshold is affected by chromaticity, vertical global orbit, and bunch spacing. The '97-10' fill pattern is quite good allowing 150 mA to be stability stored without feedback.
During our last collision day the best single bunch luminosity was 3.7x10**29/cm**2/sec with 1.2 mA in the LER and 0.4 mA in the HER. The vertical 'cap-sigma" was 16 to 19 microns and 280 microns horizontally (design = 7 and 222 respectively). With 87 bunches in each ring, the luminosity was 1.4x10**31/cm**2/sec with 76 mA in the LER and 30 mA in the HER. The HER lifetime was 240 min. and the LER 13 min. The currents 100 mA x 31 mA in 87 bunches were collided but gave a lower luminosity (0.9x10**31) due to beam-beam enlargement. Our high current collision run lasted over 90 minutes including about 6 beam-beam position scans and 25 injection top-off cycles, all without a single beam trip.
Thanks again to all. Regards, John Seeman 11/28/98
Suggestions to: John Seeman
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