NLC Intra-Pulse Fast Feedback Simon Jolly Oxford University NLC Beam Delivery Meeting July 2001

Simon Jolly Oxford University 2 Before we begin... I have stolen parts of this talk from: Glen White, Steve Smith, PT and then some…..

Simon Jolly Oxford University 3 Plan of Action Requirements of a feedback system. Current design: –Physical specs. –Signal filtering electronics. –Simulated performance. Current status and planned tests. Track reconstruction. A brief word on beam jitter. Short term and long term plans.

Simon Jolly Oxford University 4 Fast Feedback - Who needs it…? Jitter inherent in beams and accelerating structures - leads to relative position offset of beams. Position offset leads to large luminosity loss: Y position offset (  y ) Percentage Luminosity Loss

Simon Jolly Oxford University 5 Fast Feedback - System Constraints Recover significant amount of lost Luminosity. Correct offset within a single bunch train (266ns - hence ‘fast’...). Dominant time factor should be distance to IP, NOT speed of feedback - too fast for ‘analytical’ electronics. Be unaffected by intra-train jitter….. A corrective feedback system needs to:

Simon Jolly Oxford University 6 NLC Fast Feedback System System consists of 3 components: BPM (+ BPM processor). bunch charge gain adjuster. Kicker (and kicker driver). Bunch Charge Use beam-beam interaction to enhance offset measurement 4m

Simon Jolly Oxford University 7 Design of Feedback System Initial system design and “proof of principle” in Simulink simulation by Steve Smith. Glen White (Oxford) simulation makes a number of improvements: –Includes “gain” effects. –Accurate beam-beam interaction model - original flat beyond 12  (GUINEA-PIG). –Effects of intra-train (bunch-to-bunch) jitter considered. System currently only corrects position offset (no angle jitter).

Simon Jolly Oxford University 8 Simulink Block Diagram Beam parameters (posn. and charge) Beam-beam interaction BPM processor Beam kicker Delay cable Effect of kicked beam Flight of bunches from/to IP BPM to kicker transport delay

Simon Jolly Oxford University 9 BPM Processor Most signal conditioning executed by BPM processor Bunch Charge But what does it do…?

Simon Jolly Oxford University 10 BPM Electronics Band pass filterMixerLow pass filter Simulink diagram for BPM processor Local oscillator for mixer 2nd stripline 1st stripline Sum and difference

Simon Jolly Oxford University 11 BPM Signal Filtering Time (ns) Signal on BPM Mixer output Band pass filter output Low pass filter output

Simon Jolly Oxford University 12 BPM Electronics Output Time (ns) BPM processor output Position of bunch at BPM Signal from delay cable (Kicker) Kicker input (BPM + delay signal)

Simon Jolly Oxford University 13 Beam Correction at IP (Simulink) Time (ns) Vertical offset (nm) Uncorrected beam position at IP Corrected beam position at IP

Simon Jolly Oxford University 14 Effect of Feedback System Effect of the feedback system on the luminosity loss (Glen White). Y position offset (  y )

Simon Jolly Oxford University 15 What Happens Next? Bench test BPM electronics. Beam test of stripline BPM and electronics. Confirm design of kicker dimensions and power requirements - dependant upon location, train structure. Beam test of complete system (location on a need to know basis….). Reconstruction of tracks in beam test  use PT’s Collimator Wakefield Matlab routines.

Simon Jolly Oxford University 16 Collimator Wakefields (PT) 4 collimation slots used. Determination of bunch kick due to wakefield effects. To reconstruct kicks: – Measure positions of bunches (25 per step) along sector 2. –Subtract ‘reference’ track (100 bunches). –Use transport matrices to reconstruct bunch position and angle at slot. Collimator slot dimensions

Simon Jolly Oxford University 17 Reconstructed wakefield kick Collimator slot height vs. angle deviation

Simon Jolly Oxford University 18 Reconstructed kicks (slot 1)

Simon Jolly Oxford University 19 Angular Jitter on Kick Reconstruction Wakefield box slot y posn. (mm) RMS angular jitter (  r) Collimator slot height vs. angular jitter for reconstructed wakefield kicks (slot 1)

Simon Jolly Oxford University 20 2D Histogram of beam jitter A Quick Look at Position Jitter Data taken from 160 data samples over 12 days X Y 500 x 500  m

Simon Jolly Oxford University 21 X and Y jitter on SLC e - beam x distance from mean orbit posn. (  m) Histogram of jitter in xHistogram of jitter in y y distance from mean orbit posn. (  m)  x =  m  y =  m

Simon Jolly Oxford University 22 Time Dependence of Jitter Run number Beam jitter in y for 3 BPM’s  y (  m) Chart shows beam jitter (rms deviation from mean) for 3 BPM’s during 160 runs. Each point is rms of y position for 100 bunches (1 reference scan). Includes 12 days worth of data.

Simon Jolly Oxford University 23 Time Dependence of Jitter (2) Run number Beam jitter in y for 7 BPM’s BPM #

Simon Jolly Oxford University 24 And Finally... Next step is to bench test BPM electronics. Start looking at possible solutions for kicker design. Longer term: beam tests of BPM systems, kicker design and complete system. Very very long term: install system in the NLC….