《Secondary Emission Monitor working principle二次发射显示器的工作原理.ppt》由会员分享，可在线阅读，更多相关《Secondary Emission Monitor working principle二次发射显示器的工作原理.ppt（28页珍藏版）》请在三一文库上搜索。
1、Secondary Emission Monitor for very high radiation areas of LHC,Daniel Kramer for the BLM team,10.6.2008,D.Kramer BLM Audit,2,LHC Beam Loss Monitoring system, 3700 BLMI chambers installed along LHC 280 SEM chambers installed in high radiation areas: Collimation Injection points IPs Beam Dumps Apertu
2、re limits Main SEM requirements 20 years lifetime (up to 70MGray/year) Sensitivity 7E4 lower than BLMI,10.6.2008,D.Kramer BLM Audit,3,Secondary Emission Monitor working principle,Secondary electrons,Bias E field,Ti Signal electrode,Ti HV electrodes,Steel vessel (mass),Secondary Electron Emission is
3、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 ionizat
4、ion 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),10.6.2008,D.Kramer BLM Audit,4,Secondary Emission Monitor working principle,Secondary electrons
5、,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
6、 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 Sign
7、al and Bias (guard ring),10.6.2008,D.Kramer BLM Audit,5,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 indepe
8、ndent 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 a
9、nd shielding of signal path to eliminate ionization in air (otherwise nonlinear response) No direct contact between Signal and Bias (guard ring),10.6.2008,D.Kramer BLM Audit,6,Secondary Emission Monitor working principle,Secondary electrons,Bias E field,Ti Signal electrode,Ti HV electrodes,Steel ves
10、sel (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
11、*, 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),10.6.2008,D.Kramer BLM Audit,7,Seco
12、ndary 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
13、(1.5kV) Transit time 500ps 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 and avoid capture of electrons Very careful insulation and shieldi
14、ng of signal path to eliminate ionization in air (otherwise nonlinear response) No direct contact between Signal and Bias (guard ring),Incoming particle,10.6.2008,D.Kramer BLM Audit,8,SEM production assembly,All components chosen according to UHV standards Steel/Ti parts vacuum fired Detector contai
15、ns 170 cm2 of NEG St707 to keep the vacuum 10-4 mbar during 20 years Pinch off after vacuum bakeout and NEG activation (p10-10mbar) 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,Ve
16、ry high adsorbtion capacity of H2, CO, N2, O2 Not pumping CH4, Ar, He,10.6.2008,D.Kramer BLM Audit,9,Vacuum bakeout and activation cycle for SEM and BLMI,NEG inside the SEM needs additional activation at 350C Activation means releasing adsorbed gases on the surface which have to be pumped Pinchoff d
17、one during the cool down of the chamber Resulting pressure below measurement threshold (10-10mbar),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,He leak tests,Vacuum bakeou
18、t,pinchoff,10.6.2008,D.Kramer BLM Audit,10,Geant4 simulations of the SEM,Secondary Emission Yield is proportional to electronic dE/dx in the surface layer LS = (0.23 Ng)-1 g = 1.6 Z1/310-16cm2 “TrueSEY” of each particle crossing the surface boundary calculated and SE recorded with this probability C
19、orrection for impact angle included in simulation QGSP_BERT_HP as main physics model,Model calibration factor,Penetration distance of SE,Electronic energy loss,Comparison to literature values = CF = 0.8,Geant4 SEM Response function,0 impact angle,10.6.2008,D.Kramer BLM Audit,11,SEM Calibration exper
20、iment in a mixed radiation field (CERF+ test),Response of the SEM measured with 300GeV/c beam hitting 20cm copper target Setup simulated in Geant4 Response of SEM filled by AIR measured and simulated as well SEM Response expressed in absolute comparison to Air filled SEM Response = Dose in AIR SEM /
21、 output charge of SEM 0.259 +/- 0.016 Gy/count,H4 Calibration setup with Cu target and a box with 16 SEMs on a movable table,10.6.2008,D.Kramer BLM Audit,12,Calibration results,Not corrected for systematic position errors,Offset current without beam,Only 2 chambers out of 250 had higher offset curre
22、nt,Upper Limit on the SEM pressure: (equivalent to 3 of the histogram) 1bar(0.6 sigSEM / sigSEM AIR) = 0.26 mbar Pressure inside SEMs smaller than this,10.6.2008,D.Kramer BLM Audit,13,Table of SEM measurements and corresponding simulations,10.6.2008,D.Kramer BLM Audit,14,Thanks,10.6.2008,D.Kramer BL
23、M Audit,15,Backup slides,Vacuum stand in IHEP for IC production 36 ICs in parallel baked out and filled by N2,For SEMs only 18 chambers in parallel No N2 injection :o) He leak detection done before and after bakeout (and after NEG activation for SEMs),10.6.2008,D.Kramer BLM Audit,16,Beam dumped on a
24、 Closed Jaw of LHC collimator in LSS5. SEM to BLMI comparison 1.3 1013p+,Black line signal not clipped 5*_filter = 350ms,SEM,BLMI A,10.6.2008,D.Kramer BLM Audit,17,Cable crosstalks study important crosstalks caused by long cables in the LSS,Ch 68 unconnected Xtalk clearly depends on the derivation S
25、ignal peak ratio 5e-2 (26dB) (worst case) Integral ratio 4.4e-3 (47dB) Similar behavior for system A X-talks limited to 1 CFC card only!,10.6.2008,D.Kramer BLM Audit,18,Standard BLMI ARC installation,HV Power Supply,HV ground cut here,BLMI,Up to 8 BLMs connected in parallel,CFC is always close to th
26、e quadrupole,Small low pass filter in the CFC input stage,10.6.2008,D.Kramer BLM Audit,19,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,
27、SEM has not 150k protection!,10.6.2008,D.Kramer BLM Audit,20,150kOhm Rp resistor for BLMI i/o current limitation between HV capacitor & IC),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 Corresponds to 7 mGy t
28、otal loss Corresponds to 180 Gy/s (PM limit = 22 Gy/s) Slows down the signal collection DC current limited to 1500V / 1Mohm = 1.5 mA Corresponds to 26 Gy/s (total in max 8 chambers),10.6.2008,D.Kramer BLM Audit,21,BLMI and SEM in the dump line IR6 on the MKB,10.6.2008,D.Kramer BLM Audit,22,Longitudi
29、nal impact of proton beam r = 2mm Chamber tilted by 1 Simulation sensitive to beam angle and divergence Negative signal due to low energy e- from secondary shower in the wall,400 GeV Beam scan in TT20 SPS line,Integral of Simulation = 0.608 e-mm Integral of Scan2 = 0.476 e-mm,Relative difference 22%
30、,10.6.2008,D.Kramer BLM Audit,23,Prototype tests with 63MeV cyclotron beam in Paul Scherer Institute,Prototype C - more ceramics inside (no guard ring) Prototype F - close to production version Current measured with electrometer Keithley 6517A HV power supply FUG HLC14 Pattern not yet fully understo
31、od Not reproduced by simulation High SE response if U_bias 2V Geant4.9.0 simulated SEY = 25.50.8%,PSI proton beam 62.9MeV BLMS prototypes F & C Type HV dependence of SEY,10.6.2008,D.Kramer BLM Audit,24,Measurements in PS Booster Dump line with 1.4 GeV proton bunches,Older prototype measured - Type C
32、 Type F simulated Profiles integrated with digital oscilloscope 1.5kV bias voltage 80m cable length 50 termination Single bunch passage SEY measurement 4.9 0.2% Geant4.9.0 simulation 4.2 0.5%,Normalized response,10.6.2008,D.Kramer BLM Audit,25,Example loss induced by the fast moving SPS scraper. Mea
33、sured in the collimation area by the LHC BLM system 4 different monitors (2006-old electronics),10.6.2008,D.Kramer BLM Audit,26,Example of beam losses in the SPS collimation area during a collimator movement of 10um (2006) Coasting beam,2006 data CWG 19/3/07,FFT spectrum,10.6.2008,D.Kramer BLM Audit,27,SPS Coasting beam 270GeV 200um Left jaw move and FFT spectra,10.6.2008,D.Kramer BLM Audit,28,Complete FFT from the previous plot Horizontal Tune calculation from the BLM measurement - oscillations in the beam not in the BLM system,