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LHC Beam Position System - Implications for Machine Protection

LHC Beam Position System - Implications for Machine Protection. Internal MPP Review June 17 th 2010 Rhodri Jones (CERN Beam Instrumentation Group). MPP Related BPM Issues. Dependence of BPM readings on intensity Dependence of BPM readings on temperature

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LHC Beam Position System - Implications for Machine Protection

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  1. LHC Beam Position System-Implications for Machine Protection Internal MPP Review June 17th 2010 Rhodri Jones (CERN Beam Instrumentation Group)

  2. MPP Related BPM Issues • Dependence of BPM readings on intensity • Dependence of BPM readings on temperature • Sensitivity Settings for the BPM system Internal MPP Review – 17th June 2010 Rhodri Jones

  3. General Performance • Excellent availability • Only 10 channels out of 2150 currently masked (0.5%) • Rms noise too high or extreme offsets • Crates now rarely require reboot • Cause of remaining crashes still not understood • Real-time data • Now transmitted to orbit feedback at 25Hz • Modes • Currently using asynchronous IIR mode • Makes use of all data without requiring timing • Moving to synchronous mode using bunch ID can make position reading more robust but may impact on availability • Relies on fast timing & correct phase-in (seems to be reliable) • Will need input on bunch filling scheme • Can start by always measuring bunch 1 Internal MPP Review – 17th June 2010 Rhodri Jones

  4. Dependence of BPM Readings on Bunch Intensity • BPMs work on bunch to bunch basis • Only depend on bunch intensity • BPMs can be used in 2 sensitivity modes • High sensitivity • From ~ 1×109 to ~5×1010 • Low sensitivity • From ~ 5×1010 to ~2×1011 • Only changes threshold for bunch detection • No gains changed • Required to make system immune from reflections generated by imperfect cabling, connections & BPMs. • MDs have shown that • B2 behaves as expected • B1 has a grey zone between 3×1010 and 5×1010 where neither sensitivity gives required results Internal MPP Review – 17th June 2010 Rhodri Jones

  5. BPM Dependence on Intensity - Beam 2 • One nominal bunch of 1×1011 slowly scraped away using a primary collimator • Sensitivity constantly changed from high to low • Outliers due to acquisition overlapping two sensitivity ranges • Sensitivity ranges seen to overlap as expected at around 5×1010 Internal MPP Review – 17th June 2010 Rhodri Jones

  6. BPM Dependence on Intensity - Beam 1 • One nominal bunch of 1×1011 slowly scraped away using a primary collimator • 2 fills – one for low sensitivity and one for high sensitivity Low Sensitivity Dead zone where neither setting works well ×1010 0 2 4 6 8 10 12 High Sensitivity ×1010 0 2 4 6 8 10 12 Internal MPP Review – 17th June 2010 Rhodri Jones

  7. B1 Arc BPM variation - 5×1010 to 1×1011 Mean= 53mm • Stdev = 76mm • Mean= 55mm • Stdev = 80mm Internal MPP Review – 17th June 2010 Rhodri Jones

  8. B1 Arc BPM variation - 6×1010 to 1×1011 Mean= 8mm • Stdev = 44mm • Mean= 11mm • Stdev = 50mm Internal MPP Review – 17th June 2010 Rhodri Jones

  9. B1 LSS BPM variation - 6×1010 to 1×1011 Mean= 15mm • Stdev = 74mm • Mean= 20mm • Stdev = 57mm Internal MPP Review – 17th June 2010 Rhodri Jones

  10. B1 v B2 Comparison - 6×1010 to 1×1011 Mean= 8mm • Stdev = 44mm Mean= 2mm • Stdev = 48mm Arc BPMs Mean= 21mm • Stdev = 60mm Mean= 15mm • Stdev = 74mm LSS BPMs Beam Commissioning Working Group – 15th June 2010 Rhodri Jones

  11. Interlock BPMs in LSS6 – Beam 2 BPMSB : 131mm diameter stripline coupler BPMSA : 81mm diameter stripline coupler Internal MPP Review – 17th June 2010 Rhodri Jones

  12. BPM Position Dependence on Temperature • Main component known to suffer temperature dependence is the wide band time normaliser integrator card • Located on surface • Prone to relatively large temperature variation • Position encoded in pulse length 10 ± 1.5ns • Temperature affects offset & hence integral • position dependence should be minimal • Clear correlation between acquisition card temperature and position Internal MPP Review – 17th June 2010 Rhodri Jones

  13. BPM System Conclusions • Position dependence on intensity • Max variation with intensity <200mm for 6×1010 to 1×1011 • Beam 1 in high sensitivity still to be understood for 3.5×1010 to 5×1010 • Hypothesis that intensity card is influencing B1 power supplies • Position dependence on temperature • Temperature variations (~50mm / °C) • New software being tested to correct for this on-line • Other Issues • How reproducible are we? • Difficult to measure – calibration shows little variation apart from temperature • Influence of other beam on directional BPMs in the IRs • New firmware & software using synchronous mode & bunch selection being tested to overcome this • May also help overcome B1 issues in high sensitivity • Interlock BPMs in LSS6 • Need to adapt large aperture pick-up amplitudes • Work always in high sensitivity? • Would not work below 5×109 & above ~1.2×1011 • Otherwise need to learn how to cope with sensitivity switching Internal MPP Review – 17th June 2010 Rhodri Jones

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