LHC wire scanner system Run 12 experience Plans

LHC wire scanner system Run 1&2 experience Plans for Run 3 F. Roncarolo – LHC Beam Size Measurement Review (1 -Oct-2019) Thanks to: G. Trad, J. Emery, E. Bravin, R. Veness, A. Guerrero, G. Baud, M. Sapinsky, many others

CONTENTS (OF 9 YEARS IN 20 MINUTES…) ▀ ▀ ▀ Introduction to LHC WS, intensity limits Experience during Run 1 & 2 • Usage statistics • Resolution precision and accuracy • Main reliability and availability issues Plans for Run 3 FR @ Beam Size Review 01 -Oct-19 3

WIRE SCANNER MONITORS ▀ ▀ ▀ Thin wire travelling trough the beam Secondary shower from beam-wire interaction Sampling the shower intensity vs wire position gives beam profile @ LHC: Linear scanners FR @ Beam Size Review 01 -Oct-19 4

LHC BEAM WIRE SCANNERS (BWS) 8 monitors installed in IR 4 4 operational scanners + 4 installed spares Linear actuators , 1 m/s (LEP design) 30 um Carbon wires Scintillators coupled to PMTs (dynamic range covered with optical density filters in between) ‘Legacy’ control and DAQ electronics, multiplexing FR @ Beam Size Review 01 -Oct-19 BEAM 2 BWS B 2 H 1 B 2 H 2 B 2 V 1 B 2 V 2 BEAM 1 BWS B 1 H 1 B 1 H 2 B 1 V 1 B 1 V 2 BWS == Calibration Device Only available for low intensity beams 5

LHC BEAM WIRE SCANNERS (BWS) FR @ Beam Size Review 01 -Oct-19 6

INTENSITY LIMITS BWS are interceptive and therefore induce ▀ Losses ▀ Beam size increase (always ~negligible @ LHC) both depending on ▀ Wire diameter, material density, speed ▀ Energy of incident protons FR @ Beam Size Review 01 -Oct-19 7

INTENSITY LIMITS @ LHC ▀ ▀ Inj. energy 450 Ge. V : 270 e 11 p wire damage Flat top 6. 5 Te. V: 16 e 11 p BLM thresholds to protect from quench N. B. : ▀ could measure xx bunches more as wire becomes thinner with usage (sublimation, see next slide) ▀ More on this in HL-LHC presentation later FR @ Beam Size Review 01 -Oct-19 8

RUN 1 2012 – 4 TEV 22 -Aug-2012 12 -Oct-2012 22 -Nov-2012 System B 1 H (aged wire, changed during intervention to fix bellow leak) B 1 H (new wire) B 1 V (new wire) Beam Intensity 4. 29 e 12 No dump 4. 18 e 12 Dump 3. 54 e 12 BLM signal [Gy/s] 0. 0091 0. 0218 0. 0335 Losses / proton @ downstream BLM [Gy/p] 5. 4 e-19 2. 7 e-17 2. 4 e-17 new wire aged wire 16 um Dump 34 um Aged wire partially sublimated smaller diameter lower losses FR @ Beam Size Review 01 -Oct-19 9

USAGE STATISTICS FR @ Beam Size Review 01 -Oct-19 10

LHC BWS USAGE RUN 1&2 Up to 600 scans per monitor per week and Up to 350 scans per monitor per day FR @ Beam Size Review 01 -Oct-19 11

LHC BWS USAGE RUN 1&2 FR @ Beam Size Review 01 -Oct-19 12

LHC BWS USAGE RUN 1&2 ▀ Combined with wire exchange history, will help defining the operational systems for the start of Run 3 FR @ Beam Size Review 01 -Oct-19 13

PERFORMANCE FR @ Beam Size Review 01 -Oct-19 14

PERFORMANCE (INTRO) Resolution Minimum beam size variation the system is able to measure FR @ Beam Size Review 01 -Oct-19 15

PERFORMANCES (INTRO) ▀ ▀ Accuracy and precision dominated by • Wire position determination • Linearity and dynamic range of secondary shower detectors Resolution driven by • Precision • Wire diameter • Number of points per sigma FR @ Beam Size Review 01 -Oct-19 16

RESOLUTION FR @ Beam Size Review 01 -Oct-19 17

RESOLUTION LHC Fill 7220 (BSRT calibration) – 12 bunches with different emittances 450 Ge. V 6. 5 Te. V FR @ Beam Size Review 01 -Oct-19 Next slide: Look here to estimate resolution as capability to distinguish small bunches 18

RESOLUTION 5 um resolution level in meas. beam size Resolution degradation for smaller bunches (less points per sigma) FR @ Beam Size Review 01 -Oct-19 19

PRECISION FR @ Beam Size Review 01 -Oct-19 20

PRECISION LHC Fill 7220 (BSRT calibration) – 12 bunches with different emittances 450 Ge. V Next slides: Look at bunch 1200 as seen by 8 BWS @ FLAT TOP 6. 5 Te. V FR @ Beam Size Review 01 -Oct-19 21

PRECISION - FILL 7220 – BUNCH# 1200 @ FT Next slide: Look at this period (before squeeze) FR @ Beam Size Review 01 -Oct-19 22

PRECISION - FILL 7220 – BUNCH# 1200 @ FT Precision as: spread around average value FR @ Beam Size Review 01 -Oct-19 B 1 H 1 RMS = 1. 50 um B 1 H 2 RMS = 2. 90 um (0. 51 %) (0. 99 %) B 1 V 1 RMS = 2. 78 um B 1 V 2 RMS = 2. 93 um (0. 72 %) (0. 75 %) B 2 H 1 RMS = 18. 9 um B 2 H 2 RMS = 7. 69 um (6. 56 %) (2. 66 %) B 2 V 1 RMS = 6. 23 um B 2 V 2 RMS = 10. 7 um (1. 41 %) (2. 74 %) 23

PRECISION - PMT NOISE Bunch per bunch PMT acquisition resulted to be strongly biased by (low frequency) noise First patch solution (subtracting signal from empty bunch slot) was complemented by upgrade of PMT analogue electronics Situation greatly improved FR @ Beam Size Review 01 -Oct-19 24

ACCURACY FR @ Beam Size Review 01 -Oct-19 25

ACCURACY - WIRE POSITION MEASUREMENT On Spare WS B 1 H 1 (access constraint) q Measure the position of the metallic stub holding the wire, moving solidly with it during scan, using an external interferometer for displacement sensing (used in the collimators jaws). q Technique very accurate even for moving target at 1 m/s Compare wire position as seen by the potentiometer and the interferometer Laser G. Trad FR @ Beam Size Review 01 -Oct-19 26

ACCURACY - WIRE POSITION MEASUREMENT Conclusion: the (noisy) potentiometer is very accurate in measuring the linear actuator position What this does not say: Does the wire bend or vibrate during the scan ? Is any mechanical play affecting the wire position determination accuracy and precision? FR @ Beam Size Review 01 -Oct-19 27

ACCURACY - POTENTIOMETER SCALE ▀ ▀ ▀ Comparing BPM and BWS measurements during closed orbit bumps in IR 4 Linear fit gives error on potentiometer scaling factor assuming • BPMs accurate and linear • Bump model and optics between BWS and BPM perfectly known NB: for each BWS sigma meas. ~unchanged as function of bump amplitude FR @ Beam Size Review 01 -Oct-19 M. Khun, CERN-THESIS-2016 -149 28

2015: modified PMT bases with adapted capacitors improved the situation BEFORE PMT not able to pull enough charges can heavily affect overall BWS accuracy AFTER ACCURACY - PMT NONLINEARITY/SATURATION https: //indico. cern. ch/event/375626 FR @ Beam Size Review 01 -Oct-19 29

ACCURACY – COMPARISON TO EXPERIMENTS Emittance from BWS compared to emittance calculated from absolute luminosity at IP 1 and 5 during emittance scans 10 -15 % systematic not understood so far, to be taken as inspiration for more studies during Run 3 G. Trad, S. Papadopoulou et al. FR @ Beam Size Review 01 -Oct-19 30

RELIABILITY AND AVAILABILITY FR @ Beam Size Review 01 -Oct-19 31

RELIABILITY AND AVAILABILITY BWS reliability and availability during Run 1&2 affected by ▀ bellow leaks (see R. V. this afternoon) ▀ HW failures (e. g. motor power supplies) ▀ Control multiplexing (partially removed end of 2017) ▀ FW and SW hiccups • Wires stuck IN, few wire breaking • Caused lockouts of the systems and post-mortem analysis ▀ HW, FW and SW ‘patches’ allowed to finish ~smoothly Run 2 despite increased system obsolescence but I fear BWSs remain ‘scary beasts’ ‘you press a button, never know what will happen and when’ (cit. , anonymous) FR @ Beam Size Review 01 -Oct-19 32

RELIABILITY AND AVAILABILITY All wires were inspected (and then replaced) at the end of RUN 2. Some of them were found with lost tension. (few more words in RV talk this afternoon) B 2 H 1, The one with the worst precision … FR @ Beam Size Review 01 -Oct-19 A. Mariet, M. Hamami et al. 33

PLANS FOR RUN 3 FR @ Beam Size Review 01 -Oct-19 34

LIU BWS – CONTROL ELECTRONICS New BWS generation being installed in PSB, PS, and SPS Power and control electronics in new intelligent drive crate decoupled from supervising VME crate Dimensioned (HW) and optimized (FW) for high speed (>5 m/s) rotational devices FR @ Beam Size Review 01 -Oct-19 35

LIU BWS – SECONDARY SHOWER DETECTOR Multi-PMT coupled to same scintillator Each channel with fixed optical density filter 4 profiles for each scan, FW + SW to publish not saturated profiles with enough signal ▀ transparent to OP ▀ No need to manually change filters depending on beam intensity and energy FR @ Beam Size Review 01 -Oct-19 PS LHCINDIV beam, 2018 36

LHC BWS PLANS FOR RUN 3 Ongoing LHC BWS electronics CONS Adapt motor and motor coupling (outside vacuum mechanics) to new Intelligent Drive (ID) Adapt ID FW to LHC linear scanner, 1 m/s Equip one of the 4 spare scanners with prototype electronics for tests after LS 2 Cables for future control of all scanners already pulled + Add one scintillator + multi-PMT detector, readout by new acquisition system (dynamic range covered with no need to change optical filters) FR @ Beam Size Review 01 -Oct-19 D. Gudkov 37

SUMMARY ▀ ▀ Discussed about resolution, precision, accuracy • Existing BWS are on the paper very well suitable to act as reference beam size measurement with low intensity beams but remain a complicated electromechanical system My top-picks ‘issues’ • Lack of laboratory test bench able to calibrate wire position (e. g. via laser system as for injectors) • Could study wire vibrations, mechanical plays, fork deformations etc… • Lack of precision on B 2 H systems (loose wire only problem? Not clear) • Systematic disagreement w. r. t. lumi scans, not clear • Not-easy-to-use (FW, SW, OP GUI) • Obsolescence of control electronics FR @ Beam Size Review 01 -Oct-19 38

SPARES FR @ Beam Size Review 01 -Oct-19 39

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