01/30/99 Update

PEP-II January Commissioning

PEP-II Commissioning Update Jan 30, 1999

Comments on the December run: The luminosity monitor calibration has been studied and now better understood. As a result, our peak measured single bunch luminosity in December was about 1.0 (+/-0.2) x10**30/cm**2/sec with 2.0 mA in the LER and 0.26 mA in the HER or 55% of the design. The maximum luminosity in multibunch mode was 7.6 (+/-2) x10**31/cm**2/sec with 261 bunches with 260 mA in the LER and 84 mA in the HER. The luminosity in the multibunch mode scaled exactly with the number of bunches. (This multibunch running was not done with the best single bunch conditions.)

Our one month winter downtime ended January 15. During the down we replaced many of the remaining temporary vacuum chambers in the interaction region. We can now in principle go to 1.4 A in the LER and 0.5 A in the HER . We also fixed several small vacuum leaks in the LER.

The commissioning of the LER has concentrated on high current running and scrubbing of the vacuum system. The peak current in LER has just reached 601 mA in 853 bunches with a lifetime of about 60 minutes. The current is limited by two effects. Several warm vacuum chambers : one in the HER in the interaction region where the B1 radiation fans travel downstream (140 deg F) and the Be IP vacuum chamber (105 deg F) where about 200 watts are now being deposited with 1 ampere total beam current. Also, there are several locations in the LER where the local vacuum chamber pressure rises very quickly with current. One location reaches 200 nTorr between about 450 mA and 500 mA. We suspect local electron avalanche heating driven by the positron beam but HOM modes may take a part. All the LER feedback systems are working and the beam is stable and collidible to over 500 mA. The LER vacuum is significantly better than December. We have activated the TSP pumps three times and the scrubbing is working well reaching about 20 nT/amp pressure rise. The beam lifetime at 1 mA is about 310 minutes.

The HER has reached 507 mA in 522 bunches which is limited only by engineering concerns of a temporary chamber. The feedbacks are working well and the bunch stability is acceptable for collisions.

Yesterday, we had 500 mA in both rings simultaneously.

We collided for two days so far this run. We reached 6x10**31/cm**2/sec in multibunches with 380x94 mA**2 in 261 bunches. The single bunch luminosity has not been optimized. Raising the HER bunch current above 0.5 mA reduces the LER lifetime. Raising the LER bunch current to 3 mA (twice design) does not hurt the lifetime of the electron bunch but instead reduces its own lifetime. This is not yet understood. Parameter optimization and tune plane studies will occur during our next collision run.

Our present commissioning period ends Monday February 22 which starts an eleven week down to install BaBar. During this down we will install all the remaining high power chambers in the interaction region and ten beam collimators for backgrounds. Beams to PEP-II and BaBar are scheduled for the weekend of May 7.

Thanks again to all.

John Seeman

Suggestions to: John Seeman

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