09/25/00 Update

PEP-II Update September 25, 2000

PEP-II has been running steadily for BaBar data collection over the past weeks with a few machine development days included.

The solenoid winding of the straight section beam chambers is 95% finished.   There are about 500 m of coils wound so far.  It is believed that the gradual additions of these solenoids have led to our gradual luminosity increases.  The increases come from the reduction of the positron beam size at high current due to the electron cloud effect from multipacting electrons. The optimum bunch pattern used during collisions changes as more solenoids are wound to adjust to the electron cloud density.

We are now turning our attention to the effect of the LER arcs on the electron cloud.  Both solenoid and transverse fields are being considered as a cure. Recently, short test magnets have been installed and beam tests will be performed soon.  There are about 1100 m of LER Arc chamber to cover.

A new interferometer has been tested to measure the vertical beam size of the LER.  Early tests are encouraging showing strong correlation with the optical size monitor but with a better resolution.

The peak luminosity in PEP-II is now 2.64 x 10^33/cm^2/s with 1450 mA of positrons and 650 mA of electrons in 605 bunches.  In a typical day PEP-II delivers about 130 pb-1.  Our best integrated luminosity in 24 hours is 156 pb-1 and 914 pb-1 in 7 days.  PEP-II has delivered 21 fb-1 since the installation of BaBar in May 1999.

The present BaBar data collection period will end October 29 followed by eight machine development shifts.  The run will end midnight October 31.  During the three month down, a new LER RF station will be installed.  New HER high power dump and low pressure chambers will be installed.  More coils for multipacting suppression in the LER Arcs will be wound.  PEP-II will turn on again February 1, 2001.

John Seeman for the PEP-II Staff 9/25/2000

Suggestions to: John Seeman

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