06/04/99 Update

PEP-II Commissioning Update June 4, 1999

PEP-II commissioning over the past ten days has concentrated on raising the BaBar solenoid to full field and compensating the rings. Solenoid compensation is done with six skew quadrupoles on each side of the interaction region in both rings.

The solenoid was raised in 100 A steps to the full field of 4600 A or 1.5 T while small beam current beams were kept in both rings to adjust the orbits and tunes. The full field was reached late Friday May 28.

The compensation  of the solenoid in the HER went quickly with coupling, chromaticity and the orbit recovering as planned. In order to inject at 10 Hz the horizontal beam angle at the interaction region had to be adjusted. The HER has been to 100 mA with acceptable BaBar backgrounds with full field. 

The LER has had a much more difficult time compensating the solenoid and the work is on going. The solenoidal field apparently amplified optics errors in the interaction region which was partially compensated for by an induced error in the tune adjustment trombones. Chromaticity, coupling, and tune adjustments have been difficult. Many studies have been done, most of which indicate possible quadrupole strength errors in the interaction region final doublet. Last night, most of these optics errors were corrected by strengthening the permanent magnet quadrupoles at the interaction point by 1.4 %  using the electromagnetic trims. The field of the solenoid can change the strength of these magnets at the percent level but the exact amount is hard to predict. More work is planned. The LER has reached 100 mA with acceptable backgrounds. LER injection at 10 Hz has very little effect on backgrounds.

The beams were collided yesterday (before the quadrupole adjustments) for 8 hours with eight beam fills including five for BaBar data taking. The luminosity lifetime was about 60 to 100 minutes. The peak luminosity was 7.5x10**30/cm**2/sec with 100 mA in the LER and 28 mA in the HER in 174 bunches. BaBar commissioned a new DAQ software package during that time and increased their data sample by an order of magnitude.

The plans for the next few weeks call for lowering the spot sizes at the interaction point, raising the currents, and colliding about one third of the time.

John Seeman   6/4/1999

Suggestions to: John Seeman

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