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Ground Motion

F.O.N.T. Ground Motion. 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). G.R.White: 1.6.2001. F.O.N.T. Luminosity Loss at IP.

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Ground Motion

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  1. F.O.N.T. Ground Motion 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) G.R.White: 1.6.2001

  2. F.O.N.T. Luminosity Loss at IP • Relative offsets in final Quads due to fast ground motion leads to beam offsets of several sy (2.7 nm for NLC-H 490 GeV). • Correct using beam-based feedback system or by active mechanical stabilization of Quads or both. G.R.White: 1.6.2001

  3. F.O.N.T. LC Bunch Structure • Feedback system demonstrated for NLC-H 500 GeV • Can be modified for use at TESLA and CLIC G.R.White: 1.6.2001

  4. 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 G.R.White: 1.6.2001

  5. 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 G.R.White: 1.6.2001

  6. F.O.N.T. Feedback Components • BPM response peak near 714 MHz bunch spacing frequency • Kicker rise-time represents slowest component • System Design by Steve Smith (SLAC) G.R.White: 1.6.2001

  7. F.O.N.T. Feedback Simulation • Simulations performed using Simulink in Matlab G.R.White: 1.6.2001

  8. F.O.N.T. BPM Processor 3 ns rise- time G.R.White: 1.6.2001

  9. F.O.N.T. Feedback Performance Latency = 37.3 ns G.R.White: 1.6.2001

  10. F.O.N.T. Feedback Performance G.R.White: 1.6.2001

  11. F.O.N.T. Kicker Gain Optimisation Luminosity loss as function of gain input and beam offset G.R.White: 1.6.2001

  12. 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 G.R.White: 1.6.2001

  13. 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 G.R.White: 1.6.2001

  14. F.O.N.T. Effect of Angle Offset sy’= 27 mrad sy’= 27 mrad • 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 G.R.White: 1.6.2001

  15. F.O.N.T. IR Layout With FB System G.R.White: 1.6.2001

  16. 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 G.R.White: 1.6.2001

  17. 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 105 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 G.R.White: 1.6.2001

  18. 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 G.R.White: 1.6.2001

  19. F.O.N.T. Detector n Backgrounds Hits/cm2/1 MeV n equiv./yr Default IR: 6.6 ± 1.5 × 109 IR with FB: 8.6 ± 2.6 × 109 (neutrons/cm2/1 MeV n equiv./yr) VTD Layer • No significant increase in neutron flux in vertex detector area seen arising from pair background • More statistics being generated G.R.White: 1.6.2001

  20. 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 shows 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 suggested BPM and kicker installation positions • Hardware tests commencing at SLAC (Simon Jolly) • Simulations to be extended to include TESLA and CLIC G.R.White: 1.6.2001

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