07/27/00 Update

PEP-II Update July 27, 2000  

Recent work on PEP-II has concentrated on raising the peak luminosity and delivering integrated luminosity to BaBar.  

The luminosity has been steadily increased by raising the beam currents, lowering beta-y* at the collision point, and adjusting the bunch filling pattern.   The beta-y* for both rings is now 1.25 cm. Many filling patterns have been tried recently to peak the performance.  With too few bunches the beam-beam effect enlarges the LER beam size and reduces the luminosity.  With too many bunches the total ring charge is too high elevating the temperature of a few vacuum bellows and enlarging the LER beam size from electron multipacting with the electron cloud instability.  Fans are being mounted on the bellows modules.  Solenoid magnets are being wound on the LER vacuum chambers during every repair day to further suppress the electron multipacting.  The optimum filling pattern is now 606 bunches spaced every 8 nsec (4 RF buckets) distributed in 67 nine-bunch mini-trains separated by 32 nsec micro-gaps and three additional 200 to 300 nsec global gaps.

With these improvements, the peak luminosity in PEP-II has reached 2.28 x 1033 /cm2/s using 606 bunches with 1286 mA of positrons and 751 mA of electrons.

One of the primary design goals of PEP-II was to deliver 30 fb-1 in a year during a 10 month run.  Of the 300 days in ten months 78 were assigned to machine development, start-up, and down days, leaving 222 days for physics data taking.  Thus, a design integrated luminosity day is 135 pb-1. PEP-II delivered its first design day in May 2000.  To date PEP-II has delivered 12 design days.  Several of PEP-II's present records for integrated luminosity are 53.6-1 pb in an eight hour shift, 151.2 pb-1 in 24 hours, 890 pb-1 in one week, and 3.0 fb-1 in one month.  As of July 25 PEP-II has delivered a total of 16 fb-1 to BaBar.  BaBar has logged about 15 fb-1.

The present run will extend to October 30, 2000, followed by a three month down to install improved vacuum chambers near the interaction region, to install a new LER RF station, and to wrap additional solenoids on the LER vacuum chambers.  

John Seeman for the PEP-II Staff 7/27/2000    

Suggestions to: John Seeman

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