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Commissioning LHC Beam Instrumentation for Nominal Bunch Intensities Beam Commissioning Working Group June 15 th 2010 Rhodri Jones (CERN Beam Instrumentation.

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Presentation on theme: "Commissioning LHC Beam Instrumentation for Nominal Bunch Intensities Beam Commissioning Working Group June 15 th 2010 Rhodri Jones (CERN Beam Instrumentation."— Presentation transcript:

1 Commissioning LHC Beam Instrumentation for Nominal Bunch Intensities Beam Commissioning Working Group June 15 th 2010 Rhodri Jones (CERN Beam Instrumentation Group)

2 ● Report from 2 MD periods ● May 28 th : 4 hours ● 1 st go at ● BPM reading v intensity studies ● Studies on DCCT dependence on fill pattern ● Calibration of various Fast BCT modes ● June 8 th : 7 hours ● 2 nd go at ● BPM reading v intensity studies ● Studies on DCCT dependence on fill patterns ● Calibration of various Fact BCT modes ● 1 st go at ● Wire scanner timing calibration ● BGI commissioning ● PLL setting-up ● Current Status of Abort Gap Monitor High Intensity BI LHC Commissioning Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones

3 ● BPMs work on bunch to bunch basis ● Only depend on bunch intensity ● BPMs can be used in 2 sensitivity modes ● High sensitivity ● From ~ 1×10 9 to ~5×10 10 ● Low sensitivity ● From ~ 5×10 10 to ~2×10 11 ● Only changes threshold for bunch detection ● No gains changed ● Required to make system immune from reflections generated by imperfect cabling, connections & BPMs. ● 1 st MD showed that ● B2 behaved as expected ● B1 had a grey zone between 3×10 10 and 5×10 10 where neither sensitivity gave required results Dependence of BPM Readings on Bunch Intensity Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones

4 ● One nominal bunch of 1×10 11 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 5×10 10 BPM Dependence on Intensity - Beam 2 Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones

5 ● One nominal bunch of 1×10 11 slowly scraped away using a primary collimator ● 2 fills – one for low sensitivity and one for high sensitivity BPM Dependence on Intensity - Beam 1 Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones Low Sensitivity High Sensitivity Dead zone where neither setting works well × ×10 10

6 B1 Arc BPM variation - 5×10 10 to 1×10 11 Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones Mean = 55  m Stdev = 80  m Mean = 53  m Stdev = 76  m

7 B1 Arc BPM variation - 6×10 10 to 1×10 11 Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones Mean = 11  m Stdev = 50  m Mean = 8  m Stdev = 44  m

8 B1 LSS BPM variation - 6×10 10 to 1×10 11 Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones Mean = 20  m Stdev = 57  m Mean = 15  m Stdev = 74  m

9 B1 v B2 Comparison - 6×10 10 to 1×10 11 Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones Mean = 8  m Stdev = 44  m Mean = 15  m Stdev = 74  m Arc BPMs LSS BPMs Mean = 21  m Stdev = 60  m Mean = 2  m Stdev = 48  m

10 ● BPM System ● Max variation with intensity <200  m for 6×10 10 to 1×10 11 ● Beam 1 behaviour in high sensitivity still to be understood for 3.5×10 10 to 5×10 10 ● Hypothesis that intensity card is influencing B1 power supplies ● Oustanding Issues ● Temperature variations (~50  m / °C) ● New software being tested to correct for this on-line ● 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 BPM System Conclusions Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones

11 ● At these intensities the fast BCTs behave as expected ● As in SPS small % is measured in neighbouring 25ns slot ● No impact observed from bunch length variations ● 250ps to 150 ps sigma Fast BCTs at 2×10 10 protons per bunch Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones

12 ● Saturation observed during first MD ● Technical stop used to install attenuators for system B ● Response tested during second MD Saturation of the Fast BCT Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones System A Bunch Sum Intensity (High Bandwidth ) loses track at ~6×10 10 System B with added attenuators Bunch Sum Intensity stays in agreement with the DCCT Time Total Intensity

13 ● No issues observed with 2×10 10 protons per bunch ● At 1×10 11 the DCCT measurement using its highest gain range becomes dependent on the filling pattern DCCT Performance (1/2) Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones 2×10 10 per injection1×10 11 per injection Bunch at 1001 Bunch at 3001 Bunch at Grey = DCCT Blue = Fast LowBW Red = Fast HighBW (suffering from saturation)

14 ● At 1×10 11 the DCCT measuring in gain range 3 seems insensitive to the filling pattern DCCT Performance (2/2) Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones Dashed Blue= What it should be Green = BCTDC A toggling from range 3 to 4 Gray= BCTDC B toggling from range 3 to 4

15 ● Fast BCT System ● Add attenuators to operational systems suring next technical stop ● Ensure that this only affects the high bandwidth channel and not the low bandwidth providing the beam presence flag ● Need to understand the remaining calibration issues ● Why raw calibration still needs tweaking to align fast BCT with DCCT ● The cause and effect of the signal tail in the trailing 25ns slot ● Fast BCT dependence on bunch length ● Look carefully at response during ramp when no longitudinal blow-up is applied to verify that observed intensity variations with bunch length were due to saturation ● DCCT System ● Switch to gain range 3 just above 1×10 11 protons to avoid fill pattern dependence ● Currently investigating possibility to eliminate Range 4 for SMP data ● Investigations continuing for source of this problem ● Correcting the intensity stored in the logging database ● Requested by experiments ● Currently working with CO to store corrected data in logging ● Correction of known errors – e.g. DC offset & fast BCT signal tail BCT System Conclusions Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones

16 ● test Wirescanner Studies Signal Dependence on Acquisition Delay Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones B2 Horizontal B2 Vertical Slot number Need to space bunches by ~900 slots to measure individual sizes Slot selection now available from OP app.

17 ● Started testing without beam ● Effect of emergency HV shutdown on pressure ● Various scenarios tested ● One set of parameters led to a pressure rise to mbar ● Resulted in vacuum valve closure Rest Gas Ionisation Monitor (BGI) Commissioning Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones ● Conclusion ● Emergency HV shutdown procedure will be modified to ensure that it does not lead to a rise in pressure which could close the valves & dump the beam

18 ● First images seen with 2 bunches of 1×10 11 protons ● Gas pressure of mbar ● Tests then carried out on signal level with respect to main parameters ● MCP voltage, gas pressure etc. ● Not possible to vary the BGI magnet current (interlock issue to be followed-up) First Images from the BGI Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones

19 ● BBQ sensitivity is so good PLL has been put on back burner but it does have advantages ● Less likely to jump onto spurious peaks ● Can track tune without need for predefined windows ● May be easier to make compatible with damper ● Has built-in demodulation for chromaticity measurement ● Beam 2: ● Only one scan was possible in time allowed ● The scan was performed with debris of other tests (very low intensity)! ● Measurement indicates SNR better in H than V ● Would have been easy to obtain stable lock on either ● Poor look of V plane phase an artifact of wraparound due to incorrect phase offset correction ● Beam 1: ● Just few minutes available for tests on this beam ● Not possible to excite with the PLL system ● Hardware being investigated Tune PLL Commissioning Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones

20 ● A bug in the software of the LHC abort gap monitor combined with insufficient hardware interlocks led to irreparable damage to both of the installed photomultiplier tubes (PMTs) ● 2 PMTs with 2 new amplifiers have been installed ● A CERN spare and one kindly provided by the LARP collaboration (Berkeley) ● Spare PMT has lower sensitivity probably due to ageing ● Not an issue for operation ● 3 new PMTs have been ordered to arrive this summer ● New HV power supplies with output limitation are at CERN ● SW to control them currently being developed & tested ● The abort gap monitor is operational again for both beams ● It will be only be possible/safe to put the AG system into an automated mode after replacing the power supplies (next tech stop) ● Working at fixed Voltage only has small impact on system operation Status of the LHC Abort Gap Monitors Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones

21 Status of the LHC Abort Gap Monitors Beam Commissioning Working Group – 15 th June 2010 Rhodri Jones Little difference between expected signal at 450GeV and at 3.5TeV


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