Magnet Motion Produces Luminosity Loss

NLC Feedback Operation Kicker Gain Bunch Charge Measure deflected bunches with BPM and kick other beam to eliminate vertical offsets at IP Feedback loop assesses intra-bunch performance and maintains correction signal to the kicker Minimise distance of components from IP to reduce latency

Feedback Performance vs. Gain Latency ~ 37 ns

Luminosity Performance w. Feedback Lower gains gives better performance at smaller offsets, higher gains give better performance at higher offsets Vary gain dependent on observed beam conditions

Feedback Performance w./ 2-stage Gain Gains chosen automatically based on linearisation of beam- beam kick curve. Gives good luminosity performance over whole offset region.

FONT Beam Test on the NLCTA Colliding beamsSingle beam BPM Kicker BPM Processor Kicker Amplifier Round-trip Delay (short cable delays, long trip time) (shorten trip time, lengthen cable delays) NLC NLCTA 4.5m

NLCTA Layout GunChicaneStructuresBeam Dump FONT region

NLCTA FONT Installation Magnet assembly and X-band BPM installed onto NLCTA downstream of RF structures. Feedback loop Beam direction

Magnet Assembly Kicker Dipole

X-band button BPM Pickups BPM installed in NLCTA Pickups tuned to GHz

Results: 27 Sept 2002 ~x10 Improvement in Position BPM for 5 Dipole Settings After 1 Latency Period Position corrected independent of gain, then loop “turns off” As above but loop ON: Beam stays corrected until end of pulse