1. Feedback On Nano-second Timescales: An IP Feedback System for the Future Linear Collider Requirement for a fast IP beam-based feedback system Simulation results of analogue feedback design BPM processor hardware tests Impact of system in LC interaction region University of Oxford: Phil Burrows, Glen White, Simon Jolly, Colin Perry SLAC: Steve Smith, Thomas Markiewicz October 2001

2. G.R.White: 16/10/2015 F.O.N. T. From Ground Motion studies by A.Seryi et al. (SLAC) ‘Fast’ motion (> few Hz) dominated by cultural noise Concern for structures with tolerances at nm level (Final Quads) Ground Motion

3. G.R.White: 16/10/2015 F.O.N. T. Luminosity Loss at IP Relative offsets in final Quads due to fast ground motion leads to beam offsets of several s y (2.7 nm for NLC-H 500 GeV). Correct using beam-based feedback system near IP or by active mechanical stabilization of Quads or both.

4. G.R.White: 16/10/2015 F.O.N. T. LC Bunch Structure NLC-H 500 GeV TESLA 500 GeV CLIC 500 GeV Particles/Bunch x 10 10 0.752.00.4 Bunches/train1902820154 Bunch Sep (ns) 1.43370.7 s x / s y (nm) 245 / 2.7 553 / 5 202 / 2.5 Feedback system demonstrated for NLC-H 500 GeV Can be modified for use at TESLA and CLIC

5. G.R.White: 16/10/2015 F.O.N. T. Beam-Beam Interaction Beam-beam EM interactions at IP provide detectable signal Beam-beam interactions modelled with GUINEA-PIG Shown is the kick angle and percentage luminosity loss for different vertical beam offsets

6. G.R.White: 16/10/2015 F.O.N. T. Fast 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

7. G.R.White: 16/10/2015 F.O.N. T. NLC Feedback Components Stripline BPM Distance to IP Stripline radius Stripline Width Stripline length Stripline Impedance Roundtrip time 4.3 m 1 cm 4.4 mm 10 cm 50 W 0.7 ns Stripline Kicker Distance to IP Stripline radius Stripline length Stripline Impedance Roundtrip time Azimuthal coverage Drive voltage required Drive Power 100nm correction 4.3 m 6 mm 6 mm 75 cm 50 W 5 ns 120 degrees 250 mV/nm 12.5 W BPM response peak near 714 MHz bunch spacing frequency Kicker rise-time represents slowest component System Design by Steve Smith (SLAC)

8. G.R.White: 16/10/2015 F.O.N. T. Feedback Simulation Simulations performed using Simulink in Matlab

9. G.R.White: 16/10/2015 F.O.N. T. BPM Processor 3 ns rise- time

10. G.R.White: 16/10/2015 F.O.N. T. Feedback Performance Latency = 37.3 ns

11. G.R.White: 16/10/2015 F.O.N. T. Feedback Performance

12. G.R.White: 16/10/2015 F.O.N. T. Kicker Gain Optimisation Luminosity loss as function of gain input and beam offset

13. G.R.White: 16/10/2015 F.O.N. T. Luminosity Performance Lower gains gives better performance at smaller offsets, higher gains give better performance at higher offsets Vary gain dependent on observed beam conditions

14. G.R.White: 16/10/2015 F.O.N. T. Feedback Enhancements Original FB FB with Signal Averaging

15. G.R.White: 16/10/2015 F.O.N. T. Feedback Enhancements Original Feedback model Feedback with signal averaging

16. G.R.White: 16/10/2015 F.O.N. T. Feedback Enhancements Feedback performance with and without signal averaging Left: Optimum gain for different offsets Right: Luminosity loss with different offsets

17. G.R.White: 16/10/2015 F.O.N. T. Bunch Jitter Effects Introduction of random bunch-bunch jitter causes feedback system to exacerbate luminosity loss at larger gains Shown is the effect of randomly offsetting the bunches in a train about a zero offset, assuming a gaussian noise distribution

18. G.R.White: 16/10/2015 F.O.N. T. Effect of Angle Offset Beams get small additional kick if incoming with non- compensated crossing angle, also additional lumi loss Effect not addressed with this feedback system- if significant angle offset present, additional feedback system further up- stream of IP required s y’ = 27 m rad

19. G.R.White: 16/10/2015 F.O.N. T. BPM Processor Tests Hardware tests carried out at SLAC by Simon Jolly and Steve Smith Left: Simulated output of band-pass filter at 714MHz using sine- wave generator Middle: 3ns rise time of processor: mixer + 200MHz low-pass filter Right: Rise of processor and BPM signal showing approx 2ns delay due to passage of signal through mixer and filter 3ns Rise

20. G.R.White: 16/10/2015 F.O.N. T. IR Layout With FB System

21. G.R.White: 16/10/2015 F.O.N. T. IR Pair Backgrounds e + e - Pairs and g ’s produced in Beam-Beam field at IP Interactions with material in the IR produces secondary e + e -, g, and neutron radiation Study background encountered in Vertex and tracking detectors with and without FB system and background in FB system itself Use GEANT3 for EM radiation and Fluka99 for neutrons

22. G.R.White: 16/10/2015 F.O.N. T. EM Backgrounds at BPM Absorption of secondary emission in BPM striplines source of noise in Feedback system System sensitive at level of about 3 pm per electron knocked off striplines Hence, significant noise introduced if imbalanced intercepted spray at the level of 10 5 particles per bunch exists GEANT simulations suggest this level of imbalance does not exist at the BPM location z=4.3m for secondary spray originating from pair background

23. G.R.White: 16/10/2015 F.O.N. T. Detector EM Backgrounds Insertion of feedback system at z=4.3 m has no impact on secondary detector backgrounds arising from pair background Past studies suggest backgrounds adversely effected only when feedback system installed forward of z=3 m

24. G.R.White: 16/10/2015 F.O.N. T. Detector n Backgrounds Default IR: 5.5 ± 0.8 × 10 9 IR with FB: 6.6 ± 1.3 × 10 9 (neutrons/cm 2 /1 MeV n equiv./yr) No significant increase in neutron flux in vertex detector area seen arising from pair background More statistics being generated VTD Layer Hits/cm 2 /1 MeV n equiv./yr Sum Over all Layers:

25. G.R.White: 16/10/2015 F.O.N. T. Summary Ground motion moving final Quads major source of luminosity loss at a future linear collider. Fast IP feedback system simulations show considerable luminosity recovery even beyond linear kick region. Backgrounds do not seem to be an issue for detector components or the FB system itself in simulated BPM and kicker installation positions. Hardware tests ongoing at SLAC. Working towards full beam-line tests in NLCTA. Studies ongoing into improvements to feedback response and effect of mis-shaped bunches due to wakefield effects.