Secondary Emission Monitor for very high radiation areas of LHC Daniel Kramer for the BLM team D.Kramer BLM Audit2 LHC Beam Loss Monitoring system ~ 3700 BLMI chambers installed along LHC ~ 3700 BLMI chambers installed along LHC ~ 280 SEM chambers installed in high radiation areas: ~ 280 SEM chambers installed in high radiation areas: Collimation Injection points Injection points IPs Beam Dumps Aperture limits Main SEM requirements Main SEM requirements 20 years lifetime (up to 70MGray/year) Sensitivity ~7E4 lower than BLMI D.Kramer BLM Audit3 Secondary Emission Monitor working principle Secondary electrons Bias E field Ti Signal electrode Ti HV electrodes Steel vessel (mass) Secondary Electron Emission is a surface phenomenon Energy of SE (below ~ 50 eV, dominant for signal) is independent on primary energy SE are pulled away by HV bias field (1.5kV) Signal created by e- drifting between the electrodes Delta electrons do not contribute to signal due to symmetry* < mbar VHV necessary to keep ionization inside the detector negligible Very careful insulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response) No direct contact between Signal and Bias (guard ring) No direct contact between Signal and Bias (guard ring) D.Kramer BLM Audit4 Secondary Emission Monitor working principle Secondary electrons Bias E field Ti Signal electrode Ti HV electrodes Steel vessel (mass) Secondary Electron Emission is a surface phenomenon Energy of SE (below ~ 50 eV, dominant for signal) is independent on primary energy SE are pulled away by HV bias field (1.5kV) Signal created by e- drifting between the electrodes Delta electrons do not contribute to signal due to symmetry* < mbar Incoming particle VHV necessary to keep ionization inside the detector negligible Very careful insulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response) No direct contact between Signal and Bias (guard ring) No direct contact between Signal and Bias (guard ring) D.Kramer BLM Audit5 Secondary Emission Monitor working principle Secondary electrons Bias E field Ti Signal electrode Ti HV electrodes Steel vessel (mass) Secondary Electron Emission is a surface phenomenon Energy of SE (below ~ 50 eV, dominant for signal) is independent on primary energy SE are pulled away by HV bias field (1.5kV) Signal created by e- drifting between the electrodes Delta electrons do not contribute to signal due to symmetry* < mbar Incoming particle VHV necessary to keep ionization inside the detector negligible Very careful insulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response) No direct contact between Signal and Bias (guard ring) No direct contact between Signal and Bias (guard ring) D.Kramer BLM Audit6 Secondary Emission Monitor working principle Secondary electrons Bias E field Ti Signal electrode Ti HV electrodes Steel vessel (mass) Secondary Electron Emission is a surface phenomenon Energy of SE (below ~ 50 eV, dominant for signal) is independent on primary energy SE are pulled away by HV bias field (1.5kV) Signal created by e- drifting between the electrodes Delta electrons do not contribute to signal due to symmetry* < mbar Incoming particle VHV necessary to keep ionization inside the detector negligible Very careful insulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response) No direct contact between Signal and Bias (guard ring) No direct contact between Signal and Bias (guard ring) D.Kramer BLM Audit7 Secondary Emission Monitor working principle Secondary electrons Bias E field Ti Signal electrode Ti HV electrodes Steel vessel (mass) Secondary Electron Emission is a surface phenomenon Energy of SE (below ~ 50 eV, dominant for signal) is independent on primary energy SE are pulled away by HV bias field (1.5kV) Transit time 500ps Signal created by e- drifting between the electrodes Delta electrons do not contribute to signal due to symmetry* < mbar Incoming particle VHV necessary to keep ionization inside the detector negligible and avoid capture of electrons Very careful insulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response) No direct contact between Signal and Bias (guard ring) No direct contact between Signal and Bias (guard ring) Incoming particle D.Kramer BLM Audit8 SEM production assembly All components chosen according to UHV standards Steel/Ti parts vacuum fired Detector contains 170 cm 2 of NEG St707 to keep the vacuum < mbar during 20 years Pinch off after vacuum bakeout and NEG activation (p< mbar) Ti electrodes partially activated (slow pumping observed during outgassing tests) NEG St707 composed of Zr, Vn, Fe Zr flamable -> insertion after the bottom is welded Very high adsorbtion capacity of H2, CO, N2, O2 Not pumping CH4, Ar, He D.Kramer BLM Audit9 Vacuum bakeout and activation cycle for SEM and BLMI NEG inside the SEM needs additional activation at 350 C Activation means releasing adsorbed gases on the surface which have to be pumped Pinchoff done during the cool down of the chamber Resulting pressure below measurement threshold (< mbar) Resulting pressure below measurement threshold (< mbar) Vacuum bakeout NEG activation Manifold stays colder to limit the load to the pumping system Activation temperature limited by the feedthroughs Ion pump started He leak tests Vacuum bakeout pinchoff D.Kramer BLM Audit10 Geant4 simulations of the SEM Secondary Emission Yield is proportional to electronic dE/dx in the surface layer Secondary Emission Yield is proportional to electronic dE/dx in the surface layer L S = (0.23 N g ) -1 g = 1.6 Z 1/ cm 2 TrueSEY of each particle crossing the surface boundary calculated and SE recorded with this probability TrueSEY of each particle crossing the surface boundary calculated and SE recorded with this probability Correction for impact angle included in simulation Correction for impact angle included in simulation QGSP_BERT_HP as main physics model QGSP_BERT_HP as main physics model Model calibration factor Penetration distance of SE Electronic energy loss Comparison to literature values => C F = 0.8 Geant4 SEM Response function 0 impact angle D.Kramer BLM Audit11 SEM Calibration experiment in a mixed radiation field (CERF++ test) Response of the SEM measured with 300GeV/c beam hitting 20cm copper target Response of the SEM measured with 300GeV/c beam hitting 20cm copper target Setup simulated in Geant4 Setup simulated in Geant4 Response of SEM filled by AIR measured and simulated as well Response of SEM filled by AIR measured and simulated as well SEM Response expressed in absolute comparison to Air filled SEM SEM Response expressed in absolute comparison to Air filled SEM Response = Dose in AIR SEM / output charge of SEM / Gy/count / Gy/count H4 Calibration setup with Cu target and a box with 16 SEMs on a movable table D.Kramer BLM Audit12 Calibration results Not corrected for systematic position errors Offset current without beam Only 2 chambers out of 250 had higher offset current Upper Limit on the SEM pressure: 1bar*SEM AIR /10%SEM = mbar Pressure inside SEMs smaller than this D.Kramer BLM Audit13 Table of SEM measurements and corresponding simulations Test beam Test beam Measured [e-/prim] Geant4 Rel. Dif. [%] PSI 63MeV 0.27 PSB 1.4GeV TT20 400GeV e - cm e - cm 22 H4 target 3.40 LHC collimator in LSS5 of SPS 4.03 0.25Gy In progress muons 160GeV TIDV dump Long term test - D.Kramer BLM Audit14 Thanks D.Kramer BLM Audit15 Backup slides Vacuum stand in IHEP for IC production Vacuum stand in IHEP for IC production 36 ICs in parallel baked out and filled by N2 36 ICs in parallel baked out and filled by N2 For SEMs only 18 chambers in parallel For SEMs only 18 chambers in parallel No N 2 injection :o) No N 2 injection :o) He leak detection done before and after bakeout (and after NEG activation for SEMs) He leak detection done before and after bakeout (and after NEG activation for SEMs) D.Kramer BLM Audit16 Beam dumped on a Closed Jaw of LHC collimator in LSS5. SEM to BLMI comparison p + Black line signal not clipped 5* _filter = 350ms SEM BLMI A D.Kramer BLM Audit17 Cable crosstalks study important crosstalks caused by long cables in the LSS Ch 6..8 unconnected Ch 6..8 unconnected Xtalk clearly depends on the derivation Xtalk clearly depends on the derivation Signal peak ratio 5e-2 (26dB) (worst case) Signal peak ratio 5e-2 (26dB) (worst case) Integral ratio 4.4e-3 (47dB) Integral ratio 4.4e-3 (47dB) Similar behavior for system A Similar behavior for system A X-talks limited to 1 CFC card only! X-talks limited to 1 CFC card only! D.Kramer BLM Audit18 Standard BLMI ARC installation HV Power Supply HV ground cut here BLMI Up to 8 BLMs connected in parallel CFC is always close to the quadrupole Small low pass filter in the CFC input stage D.Kramer BLM Audit19 BLMI / SEM installation for collimation areas 6 HV capacitors in parallel HV capacitor removed 150k for current limitation 280pF = chambers capacity 8 chambers in 1 NG18 cable (up to 700m) ~25pF = SEMs capacity SEM has not 150k protection! D.Kramer BLM Audit20 150kOhm R p resistor for BLMI i/o current limitation between HV capacitor & IC) Limits the peak current on the chamber input to 1500 / 150k = 10mA Limits the peak current on the chamber input to 1500 / 150k = 10mA Fast loss has only the Chamber charge available 280pF * 1500V = 0.4 uC Fast loss has only the Chamber charge available 280pF * 1500V = 0.4 uC Corresponds to ~ 7 mGy total loss Corresponds to ~ 180 Gy/s (PM limit = 22 Gy/s) Slows down the signal collection Slows down the signal collection DC current limited to 1500V / 1Mohm = 1.5 mA DC current limited to 1500V / 1Mohm = 1.5 mA Corresponds to ~ 26 Gy/s (total in max 8 chambers) D.Kramer BLM Audit21 BLMI and SEM in the dump line IR6 on the MKB D.Kramer BLM Audit22 Longitudinal impact of proton beam Longitudinal impact of proton beam r = 2mm r = 2mm Chamber tilted by ~1 Chamber tilted by ~1 Simulation sensitive to beam angle and divergence Simulation sensitive to beam angle and divergence Negative signal due to low energy e- from secondary shower in the wall Negative signal due to low energy e- from secondary shower in the wall 400 GeV Beam scan in TT20 SPS line Integral of Simulation = e-mm Integral of Scan2 = e-mm Relative difference 22% D.Kramer BLM Audit23 Prototype tests with 63MeV cyclotron beam in Paul Scherer Institute Prototype C -> more ceramics inside (no guard ring) Prototype C -> more ceramics inside (no guard ring) Prototype F -> close to production version Prototype F -> close to production version Current measured with electrometer Keithley 6517A Current measured with electrometer Keithley 6517A HV power supply FUG HLC14 HV power supply FUG HLC14 Pattern not yet fully understood Pattern not yet fully understood Not reproduced by simulation High SE response if U_bias > 2V High SE response if U_bias > 2V Geant4.9.0 simulated SEY = 25.5 0.8% Geant4.9.0 simulated SEY = 25.5 0.8% PSI proton beam 62.9MeV BLMS prototypes F & C Type HV dependence of SEY D.Kramer BLM Audit24 Measurements in PS Booster Dump line with 1.4 GeV proton bunches Older prototype measured - Type C {Type F simulated} Older prototype measured - Type C {Type F simulated} Profiles integrated with digital oscilloscope Profiles integrated with digital oscilloscope 1.5kV bias voltage 80m cable length 50 termination Single bunch passage SEY measurement SEY measurement 4.9 0.2% Geant4.9.0 simulation Geant4.9.0 simulation 4.2 0.5% Normalized response