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Current status of the optical based SPS and LHC BGI profile monitors
J.Storey, R.Jones, S.Levasseur, H.Sandberg G.Schneider (CERN BE-BI)
IPM17, 22nd May 2017
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Talk outline.
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1. Design overview.
2. Experience and status of the CERN optical based:
• SPS BGI profile monitors.
• LHC BGI profile monitors.
3. Outlook.
Beam Gas Ionisation (BGI) profile monitor = IPM
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Design overview.
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EBe-
Vacuum
MCP
Phosphor
Prism
e-
𝜸
Magnet (B=0.2T)
Window
Optics
Inte
nsifi
er+C
amer
a
CID
MCP
30m
Camera Control
(Surface)
150m
Video Digitisation(Surface)
High Voltages (Surface)
Video Amplifier (Tunnel)
150mEGP
-2.0 kV (Cathode)
+2.0 kV (MCP in)+2.6 kV (MCPout)+6.0 kV (Phosphor)
-1.9 kV (EGP out)-1.8 kV (EGP in)
150m
CameraControl (Tunnel)
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Field cage & MCP/Phosphor “Amplifier”.
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NEG coated ceramic electrodes
SHV feedthroughs
EGP
Vacuum flange with
helicoflex seal
“Amplifier assembly”
MCP + Prism coated with
phosphor & Al mirror
UHV viewport
15 kV HV feedthrough
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Vacuum chamber, optical system & camera.
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Vacuum chamber with
viewport
Dipole magnet (0.2T) in
retracted position
Prism viewed through opening in dipole magnet
Optical system + Thermo Fisher Scientific radiation hard (1Mrad) intensified
camera (gate down to 10ns)
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SPS BGI profile monitors.
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BIPMH.51634 “Horizontal” BIPMV.51734 “Vertical”
• Since 2015 same design as LHC BGI’s except no EGP calibration source.• Dipole magnet & corrector provides 0.2 T magnetic field.
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Problems encountered in 2015/2016.
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Failure of Thermo Scientific intensified camera readout electronics: • Not designed for operation in radiation environment.• Solution: Move electronics to lower radiation areas in the tunnel & minimise
time system is active by means of a remote relay.
Limited gain of Thermo Scientific intensified camera due to intensifier ageing: • Short term fix: Replaced camera intensifier. • Medium term: Optimise use of device to minimise degradation.• Long term: Replace with “something else”.
Failure of VME card that controls in-house HV supply: • Solution: Now use Siemens PLC based system to control HV supply.
Same for MCP & phosphor
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New common slow control & environmental monitoring system for CERN BGI’s.
PLC control system based on CERN standard Siemens S7 PLC, provides reliable:• Control & limits on high voltages.• Remote control of relays to turn on/off:
• Camera and camera readout boxes.• High voltage power supplies.• Video amplifiers.
• Temperature readout.• Cooling control & status (PS BGI).
Common PLC control system used for all PS, SPS & LHC BGI’s.
Based on SILECs (BE/CO) framework: • Full control through SILECs C++ client interface. • FESA classes developed.
BGI PLC based slow control system
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Summary of 2016 run.
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• By the end of 2016 run reasonable signal acquired from both horizontal and vertical BGI profile monitors for low & high intensity ion and proton beams.
Horizontal BGI raw image and beam profile
Vertical BGI raw image and beam profile
Relative vertical & horizontal emittance growth during the cycle
Figures from Hannes Bartosik and Alexander Huschauer (BE-ABP).
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SPS BGI’s: Summary of operational experience.
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Problems encountered & solved: • Failure of Thermo Scientific intensified camera readout electronics.• Failure of legacy VME based HV control cards.• Transmission of video signal.
Known limitations: • Ageing of intensified cameras.• Ageing of the MCP.• Ageing of the phosphor.
Aims for 2017: • Establish routine operational use.
Avoid these limitations with pixel detector technology
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LHC BGI profile monitors.
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• Motivation:• Ion beams (synchrotron light not available at injection energy).• Study emittance blow-up during the ramp for proton beams.
• 4 x BGI’s: Horizontal & Vertical for B1 + Horizontal & Vertical for B2.• Installed in 2007/8, operated throughout Run 1.• Not been operationally used so far in Run 2; same problems as SPS + other issues.
LHC BGI B1 Horizontal.
Same as SPS BGI’s, except:• EGP electron calibration source.• Neon gas injection providing
10-8 mbar pressure bump.
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Experience from LHC Run I:Work of M.Sapinski, D.Vilsmeier, B.Dehning.
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Measured beam profile shape is deformed for very high brightness LHC beams.
Proposed solutions:
1. Interquartile method • Okay for beams sizes > 0.3 mm.
2. Stronger magnet • Need ~1T → expensive for the aperture size needed for optical based BGI.
3. Determine gyro-radius with “electron sieve” • Filter above MCP with holes of various hole diameter.
Ref. http://accelconf.web.cern.ch/AccelConf/HB2014/papers/mopab42.pdf
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Heating problem.
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BGI temperature vs beam intensity
beam intensity (1014 p)
tem
pera
ture
(℃)
• Temperature sensor installed on prism support.• Prism is the substrate for P46 phosphor and
aluminium mirror that reflects light towards viewport.
Study by Benoit Salvant (BE-ABP).
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Vacuum gauge and Beam Loss Monitor (BLM) measurements close to the BGI.
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beam intensity
LHC dipole magnet current
beam loss close to BGI
vacuum pressure close to BGI
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Broken prism.
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• All four LHC BGI’s removed for inspection during 2016/17 winter technical stop.
• Fused silica prism broken on all 4 x LHC BGI’s.
Aluminium prism support.Broken fused silica prism.
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LHC BGI power loss with NEG coated electrodes.
16Study by Thomas Kaltenbacher & Christine Vollinger (BE-RF).
Impedance spectrum in red (HFSS)
LHC beam spectrum in blue
Broadband resonances → Power loss = 53.6 W
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LHC BGI power loss with metal electrodes.
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Resonance overlap with beam harmonic at 480 MHz → Power loss = 205 W power loss.
Study by Thomas Kaltenbacher & Christine Vollinger (BE-RF).
Impedance spectrum in red (HFSS)
LHC beam spectrum in blue
SPS metal electrode
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Ageing of Phosphor, MCP & Intensifier.
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Phosphor coating burn off. Image recorded with EGP electron source Lead ion beam
Ageing effects observed in Phosphor, MCP and Intensifier, leads to:• Inhomogeneous gain → Correction with EGP “standard candle”, however, EGP
breaks & homogeneity of source not known. • Lower sensitivity.
Solutions:• Short term - optimise operational use.• Long term - replace with “something else” ( e.g. pixel detector ).
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Conclusion & outlook: LHC BGI’s.
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LHC BGI’s:• Aim to re-install LHC BGI’s during 2017/18 winter shutdown.• Source of prism heating identified:• Not limiting to machine operation (slight pressure rise)• More of an issue for detector components
• Studying design changes to reduce power loss• Not obvious as this comes from cage design
• Prism breaking mechanism identified:• Working on redesign
• Current design okay for ion beams but operationally limited by profile broadening for proton beams:• Could be solved by addition of stronger magnet (~2T -> superconducting magnet)• Significant investment that will depend on future operational requirements.
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SPS BGI’s:• Reasonable signals acquired for both horizontal and vertical devices in 2016.• No signs of prism heating problem.• Aim to fulfil operational requirements this year.
Conclusion & outlook: SPS BGI’s.
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Spare Slides
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Original 2007 MCP / Phosphor / Prism amplifier assembly photos.
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