NLC Intra-Pulse Fast Feedback

1. NLC Intra-PulseFast Feedback Simon Jolly Oxford University NLC Beam Delivery Meeting July 2001

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. 100 80 60 Percentage Luminosity Loss 40 20 0 10 20 30 40 Y position offset (sy) 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: Simon Jolly Oxford University

5. Fast Feedback - System Constraints A corrective feedback system needs to: • 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….. Simon Jolly Oxford University

6. 4m Bunch Charge NLC Fast Feedback System Use beam-beam interaction to enhance offset measurement • System consists of 3 components: • BPM (+ BPM processor). • bunch charge gain adjuster. • Kicker (and kicker driver). 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 12s (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. Beam parameters (posn. and charge) BPM to kicker transport delay BPM processor Beam-beam interaction Delay cable Flight of bunches from/to IP Effect of kicked beam Beam kicker Simulink Block Diagram Simon Jolly Oxford University

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

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

11. Signal on BPM Mixer output Low pass filter output Band pass filter output BPM Signal Filtering 5 10 15 20 25 30 Time (ns) Simon Jolly Oxford University

12. Signal from delay cable (Kicker) Kicker input (BPM + delay signal) Position of bunch at BPM BPM processor output BPM Electronics Output 0 100 200 266 Time (ns) Simon Jolly Oxford University

13. Uncorrected beam position at IP Corrected beam position at IP Beam Correction at IP (Simulink) 0 -2 Vertical offset (nm) -4 -6 -8 0 100 200 266 Time (ns) Simon Jolly Oxford University

14. Effect of Feedback System Y position offset (sy) Effect of the feedback system on the luminosity loss (Glen White). 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 4.0 Collimator slot height vs. angular jitter for reconstructed wakefield kicks (slot 1) 3.5 3.0 2.5 2.0 1.5 RMS angular jitter (mr) 1.0 0.5 0 -1.4 -1 -0.5 0 0.5 1 1.4 Wakefield box slot y posn. (mm) Simon Jolly Oxford University

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

21. X and Y jitter on SLC e- beam Histogram of jitter in x Histogram of jitter in y sx = 17.65 mm sy = 14.34 mm -100 -50 0 50 100 -100 -50 0 50 100 x distance from mean orbit posn. (mm) y distance from mean orbit posn. (mm) Simon Jolly Oxford University

22. Time Dependence of Jitter Beam jitter in y for 3 BPM’s 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. sy (mm) Simon Jolly Oxford University Run number

23. Time Dependence of Jitter (2) Beam jitter in y for 7 BPM’s BPM # 801 631 511 411 301 146 114 0 40 80 120 160 Run number 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…. Simon Jolly Oxford University