Intra-Pulse Beam-Beam Scans at the NLC IP Update date Multibunch (ATF) results) Chip status Delete costs Get better drawing of cavity More details of cavity BPM scheme Steve Smith Snowmass 2001

Beam-Beam Scans Ultimate collider diagnostic Some Limitations: Spots sizes Alignment Waists Etc. etc. etc… Some Limitations: Takes lots of time at one measurement per pulse train Sensitive to drifts over length of scan Machine drifts low frequency noise Can we do a scan in one bunch train? Increase utility of diagnostic by increasing speed Reduce sensitivity to drift and low frequency noise Yes Leverage hardware from intra-pulse IP feedback.

Intra-pulse Feedback Fix IP jitter within the crossing time of a bunch train (250 ns) BPM measures beam-beam deflection on outgoing beam Fast (few ns rise time) Precise (~micron resolution) Close (~4 meters from IP?) Kicker steers incoming beam Close to IP (~4 meters) Close to BPM (minimal cable delay) Fast rise-time amplifier Feedback algorithm to converge within bunch train.

Intra-Pulse Feedback

Intra-Pulse Feedback (with Beam-Beam Scan & Diagnostics)

Single-Pulse Beam-Beam Scan Fast BPM and kicker needed for interaction point stabilization Open the loop and program kicker to sweep beam Digitize fast BPM analog output Acquire beam-beam deflection curve in a single machine pulse Eliminates inter-pulse jitter from the beam-beam scan. Use to Establish collisions Measure IP spot size Waist scans. What else?

Beam-Beam Scan Beam bunches at IP: blue points BPM analog response: green line

Conclusions Given Intra-Pulse Interaction Point Feedback, we have tools to perform beam-beam scans within the bunch train. Speeds up beam-beam scans by an order of magnitude, maybe more. Increases the number of parameters which can be optimized by beam-beam scans, or the optimization update frequency. Reduces low frequency noise in beam-beam scans Machine drifts 1/f noise Valuable Cheap!

Limits to Beam-Beam Feedback Must close loop fast Propagation delays are painful Beam-Beam deflection slope flattens within 1 s Feedback converges too slowly beyond ~ 20 s to make a difference in luminosity May be able to fix misalignments of 100 nm with moderate kicker amplifiers Amplifier power goes like square of misalignment

Beam-Beam Deflection

Simulated BPM Processor Signals BPM Pickup (blue) Bandpass filter (green) and BPM analog output (red)

Beam Position Monitor Stripline BPM 50 Ohm 6 mm radius 10 cm long 7% angular coverage 4 m from IP Process at 714 MHz Downconvert to baseband (need to phase BPM) Wideband: 200 MHz at baseband Analog response with <3ns propagation delay (plus cable lengths)

Fast BPM Processor

Stripline Kicker Baseband Kicker Parallel plate approximation Q = 2eVL/pwc (half the kick comes from electric field, half from magnetic) 2 strips 75 cm long 50 Ohm / strip 6 mm half-gap 4 m from IP Deflection angle Q = eVL/pwc = 1 nr/volt Displacement at IP d = 4 nm/volt Voltage required to move beam 1 s (5 nm) 1.25 volts (30 mW) 100 nm correction requires 12.5 Watts drive per strip Drive amp needs bandwidth from 100 kHz to 100 MHz

Capture transient from 2 s initial offset

Capture Transient Capture transient from 10 s initial offset (gain increased to improve large offset capture)