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

Commissioning LHC Beam Instrumentation for Nominal

Bunch Intensities

Beam Commissioning Working Group

June 15th 2010

Rhodri Jones

(CERN Beam Instrumentation Group)

● Report from 2 MD periods● May 28th : 4 hours

● 1st go at● BPM reading v intensity studies● Studies on DCCT dependence on fill pattern● Calibration of various Fast BCT modes

● June 8th : 7 hours● 2nd go at

● BPM reading v intensity studies● Studies on DCCT dependence on fill patterns● Calibration of various Fact BCT modes

● 1st 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 – 15th June 2010 Rhodri Jones

● 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.

● 1st MD showed that● B2 behaved as expected● B1 had a grey zone between 3×1010 and 5×1010 where neither

sensitivity gave required results

Dependence of BPM Readings on Bunch Intensity


● 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

BPM Dependence on Intensity - Beam 2


02:21 02:35 02:48 03:01 03:15 03:280

1

2

3

4

5

6

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9

10x 10

10

UTC Time (2010-05-28)

Inte

nsity

(p/b

unch

)

B2 high sens

B2 low sens

5.1

5.2

5.3

5.4

5.5

5.6

5.7

5.8

5.9

x 1010

UTC Time (2010-05-28)

Inte

nsity

(p/b

unch

)

B2 high sens

B2 low sens

● One nominal bunch of 1×1011 slowly scraped away using a primary collimator● 2 fills – one for low sensitivity and

one for high sensitivity

BPM Dependence on Intensity - Beam 1


Low Sensitivity

High Sensitivity

Dead zone where neither setting works well

0 2 4 6 8 10 12×1010

0 2 4 6 8 10 12×1010

B1 Arc BPM variation - 5×1010 to 1×1011


Mean = 55mmStdev = 80mm


B1 Arc BPM variation - 6×1010 to 1×1011




B1 LSS BPM variation - 6×1010 to 1×1011




B1 v B2 Comparison - 6×1010 to 1×1011




Arc BPMs

LSS BPMs



● BPM System● Max variation with intensity <200mm for 6×1010 to 1×1011

● Beam 1 behaviour in high sensitivity still to be understood for 3.5×1010 to 5×1010

● Hypothesis that intensity card is influencing B1 power supplies

● Oustanding Issues● Temperature variations (~50mm / °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


● 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 2×1010 protons per bunch


● Saturation observed during first MD● Technical stop used to install attenuators for system B● Response tested during second MD

Saturation of the Fast BCT


System A Bunch Sum Intensity

(High Bandwidth ) loses track at

~6×1010

System B with added attenuators

Bunch Sum Intensity stays in agreement with the DCCT

Time

Tota

l Int

ensi

ty

● No issues observed with 2×1010 protons per bunch

● At 1×1011 the DCCT measurement using its highest gain range becomes dependent on the filling pattern

DCCT Performance (1/2)


2×1010 per injection 1×1011 per injection

Bunch at 1001

Bunch at 3001

Bunch at 11001

Grey = DCCTBlue = Fast LowBWRed = Fast HighBW (suffering from saturation)

● At 1×1011 the DCCT measuring in gain range 3 seems insensitive to the filling pattern

DCCT Performance (2/2)


Dashed Blue = What it should beGreen = BCTDC A toggling from range 3 to 4Gray = BCTDC B toggling from range 3 to 4

● 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 1×1011 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


● test

Wirescanner StudiesSignal Dependence on Acquisition Delay


B2 Horizontal

B2 Vertical1

50

100

800

50

1

1000

800Slot number

Need to space bunches by ~900 slots to measure individual sizes

Slot selection now available from OP app.

● Started testing without beam● Effect of emergency

HV shutdown on pressure

● Various scenarios tested

● One set of parameters led to a pressure rise to

10-6 mbar● Resulted in vacuum

valve closure

Rest Gas Ionisation Monitor (BGI) Commissioning


● 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

● First images seen with 2 bunches of 1×1011 protons

● Gas pressure of 10-8 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


● 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


● 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


Status of the LHC Abort Gap Monitors


Little difference between expected signal at 450GeV and at 3.5TeV

Documents

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