12/18/98 Update
12/18/98 Update
The fall 1998 PEP-II commissioning run of seven weeks ended Tuesday December 15.
The Low Energy Ring (LER) achieved many milestones. The highest beam current was 415 mA in 291 bunches. The beam lifetime was 20 minutes at 415 mA, 63 minutes at 150 mA, and 150 minutes at 1 mA. The integrated beam current for the seven week run was 20 amp-hours. The transverse beam orbits were corrected to below 1 mm rms. The interaction region vertical beta was set to the design 1.5 cm value. The transverse and longitudinal feedback systems were commissioned. The RF system worked well at the 400 mA level. The vacuum system shows significant scrubbing. The TSP (titanium sublimation pumps) were activated several times. With uniformly filled bunches around the ring, the positron beam was quite stable.
The High Energy Ring (HER) finished the run with a peak current of 323 mA in 261 bunches with a lifetime of about 400 minutes. ( 261 bunches is a 291 bunch uniform fill around the ring with a 30 bunch "ion gap".) This beam was sufficiently stable for collisions. The transverse, longitudinal, and RF feedbacks were all working.
The background measurement group took data for both HER and LER. The HER measurements are now maturing and indicate approximate agreement with recent simulations giving a factor of five to ten over the CDR predicted levels. Initial background measurements in the LER were taken which indicate that, although they are high, the backgrounds should be reduced significantly with improved vacuum level and collimation.
We succeeded in colliding 261 bunches with 260 mA in the LER and 84 mA in the HER. The luminosity monitor gave a reading of 2.7 x 10**31/cm**2/sec give or take a factor of two (systematic error on the calibration). The measured beam sizes (sigmas) at the interaction point were 10 microns in the vertical and 226 microns in the horizontal. These sizes were the average of the two rings. Given these measured sizes and the beam currents we calculate a luminosity of about 9 x 10**31/cm**2/sec given or take 30%. The difference in these two luminosity values is being studied. We also investigated several locations in the tune plane, various interaction region tuning variables (dispersion, coupling, steering,...), and beam-beam backgrounds. The tuneshift parameters are about 0.01 to 0.025 horizontally and 0.005 to 0.015 vertically.
The near term schedule is a) a short down from December 15 to January 15 to replace a few temporary chambers near the IR to allow 1 Amp in the LER and 0.5 Amp in the HER, b) a January 15 to February 15 PEP-II only run , c) down from February 15 to May 1 to install BaBar, and d) a May 1 to August 31 run with BaBar.
A very warm thank you to all and Season's Greetings ---- John Seeman Dec. 12, 1998
Suggestions to: John Seeman
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