1. 2.11.2007 IEEE NSS 2007 D.Kramer 1 Very High Radiation Detector for the LHC BLM System based on Secondary Electron Emission Daniel Kramer, Eva Barbara Holzer, Bernd Dehning, Gianfranco Ferioli CERN AB-BI

2. 2.11.2007 IEEE NSS 2007 D.Kramer2 LHC Beam Loss Monitoring system ~ 3700 BLMI chambers installed along LHC ~ 3700 BLMI chambers installed along LHC ~ 280 SEM chambers required for high radiation areas: ~ 280 SEM chambers required for high radiation areas: –Collimation –Injection points –IPs –Beam Dumps –Aperture limits Main SEM requirements Main SEM requirements –20 years lifetime (up to 70MGray/year) –Sensitivity ~3E4 lower than BLMI

3. 2.11.2007 IEEE NSS 2007 D.Kramer3 LHC Beam Loss Monitoring system ~ 3700 BLMI chambers installed along LHC ~ 3700 BLMI chambers installed along LHC ~ 280 SEM chambers required for high radiation areas: ~ 280 SEM chambers required for high radiation areas: –Collimation –Injection points –IPs –Beam Dumps –Aperture limits Main SEM requirements Main SEM requirements –20 years lifetime (up to 70MGray/year) –Sensitivity ~3E4 lower than BLMI

4. 2.11.2007 IEEE NSS 2007 D.Kramer4 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* < 10 -4 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)

5. 2.11.2007 IEEE NSS 2007 D.Kramer5 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* < 10 -4 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)

6. 2.11.2007 IEEE NSS 2007 D.Kramer6 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* < 10 -4 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)

7. 2.11.2007 IEEE NSS 2007 D.Kramer7 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* < 10 -4 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)

8. 2.11.2007 IEEE NSS 2007 D.Kramer8 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* < 10 -4 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) Incoming particle

9. 2.11.2007 IEEE NSS 2007 D.Kramer9 SEM production assembly All components chosen according to UHV standards Steel parts vacuum fired Detector contains 170 cm 2 of NEG St707 to keep the vacuum < 10 -4 mbar during 20 years Pinch off after 350 °C vacuum bakeout and NEG activation (p<10 -10 mbar) Ti electrodes partially activated (slow pumping observed)

10. 2.11.2007 IEEE NSS 2007 D.Kramer10 Simulations in Geant4 Detailed Geometry of SEM F type implemented Detailed Geometry of SEM F type implemented –Signal electrode covered by thin layer of TiO 2 Photo-Absorption-Ionization module used for production of delta electrons Photo-Absorption-Ionization module used for production of delta electrons QGSP_BERT_HP used as main physics list QGSP_BERT_HP used as main physics list Signal generation done by Signal generation done by –calculating charge balance on signal electrode –recording “True SE” produced by custom generator Production threshold for e + /e - set to 9  m Production threshold for e + /e - set to 9  m

11. 2.11.2007 IEEE NSS 2007 D.Kramer11 Semi empirical approach using simplified Sternglass formula 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 1/3 10 -16 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 Fast  electrons considered as other primaries Fast  electrons considered as other primaries Model calibration factor Penetration distance of SE Electronic energy loss Comparison => C F = 0.8

12. 2.11.2007 IEEE NSS 2007 D.Kramer12 Simulated response curves for different particle types Geant4 version 8.1.p01 Geant4 version 8.1.p01 30k primaries for each energy point 30k primaries for each energy point Longitudinal impact Longitudinal impact Gaussian beam Gaussian beam –  r = 2mm e - absorbed in electrode

13. 2.11.2007 IEEE NSS 2007 D.Kramer13 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 Negative signal due to low energy e- from secondary shower 400 GeV Beam scan in TT20 SPS line

14. 2.11.2007 IEEE NSS 2007 D.Kramer14 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 Negative signal due to low energy e- from secondary shower 400 GeV Beam scan in TT20 SPS line chamber diameter

15. 2.11.2007 IEEE NSS 2007 D.Kramer15 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

16. 2.11.2007 IEEE NSS 2007 D.Kramer16 Measurements in PS Booster Dump line with 1.4 GeV proton bunches Older prototype used - Type C Older prototype used - Type C 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

17. 2.11.2007 IEEE NSS 2007 D.Kramer17 BLMS compared to reference radiation monitor ACEM (Aluminum Cathode Electron Multiplier tube) BLMS compared to reference radiation monitor ACEM (Aluminum Cathode Electron Multiplier tube) ACEM not directly in the beam ACEM not directly in the beam Rise/fall time < 50 ns Rise/fall time < 50 ns –Dominated by unknown intensity distribution Normalized intensity 1.3 10 19 p + /s Normalized intensity 1.3 10 19 p + /s SEM response to single proton bunch of 2.16 10 13 protons with 160ns length Measurements in PS Booster Dump line with 1.4 GeV proton bunches

18. 2.11.2007 IEEE NSS 2007 D.Kramer18 Conclusions The BLMS detector was successfully tested in different proton beams The BLMS detector was successfully tested in different proton beams Geant4 simulations are in good agreement with these experiments Geant4 simulations are in good agreement with these experiments –=> chosen model is validated Sign change of output current possible under very specific circumstances Sign change of output current possible under very specific circumstances Verification measurements in mixed radiation field of LHC test collimation area in SPS are ongoing Verification measurements in mixed radiation field of LHC test collimation area in SPS are ongoing 360 BLMS Detectors were produced in IHEP Protvino and will be tested soon 360 BLMS Detectors were produced in IHEP Protvino and will be tested soon