Injection Efficiency Tune Scans in CHESS and CESRc Optics
4 August 2004
The injection simulation code has undergone recent updates to include the effects of beam-beam interactions and
synchrotron oscillations. The results presented here were obtained using the present lattices for CHESS and
CESRc optics: chess_20040704_v04 and hibetainj_20040628_v01. Horizontal tune values were scanned to see
how the the synchrobetatron sideband at Qh=0.5+Qz/2 affects the injection efficiency. Synchrotron tunes
of 0.054 (21 khz) were used for CHESS optics and 0.089 (35 khz) for CESRc. Two hundred injected particles
were tracked for 1000 turns each. A current for each of the 9x4 positron bunches of 5 mA/bunch was assumed for CHESS and of 2 mA/bunch for CESRc. Results were
calculated for a single injected electron bunch: t1.b1.
The CHESS design tunes are Qh=0.55 and Qv=0.60. Qh was scanned in steps of 0.002 between 0.51 and 0.57. Each tune point required about 30 minutes of computing
time on cesr66 or cesr68. The first plot shows that the injection efficiency is 80-95% except for Qh=0.526, where it is about 25%. The second plot shows that
this loss occurs primarily near 18W. This is also true for the losses at nearby tune values
where the efficiency is much better. At the design tune of 0.55, the efficiency
is 95% and the loss occurs primarily at 34E.
For the CESRc optics, each tune point requires five hours of computing time,
presumably spent primarily tracking electrons through the wigglers. The effect of the synchrotron
sideband is not evident, as shown in the fourth plot. It would be expected
at Qh=0.5445, and does not appear at either 0.544 or 0.545. I am now
running a job with Qh exactly set to 0.5+0.089/2 to see if the effect might
simply be very narrow in Qh. In general the injection efficiency is very
good in CESRc optics, generally about 85-95% for Qh between 0.51 and 0.56.
At the design tune values of Qh=0.52 and Qv=0.575, the efficiency is 87%,
with the loss scattered throughout the ring, biggest at 8W, 5E, and 44E.
Creation date: 08/06/04.