SecondaryEmissionMonitorworkingprinciple二次发射显示器的工作原理

1、10.6.20081LHC Beam Loss Monitoring system10.6.20082Secondary Emission Monitor working principleSecondary electronsBias E fieldTi Signal electrodeTi HV electrodes Steel vessel (mass) Secondary Electron Emission is a surface phenomenon Energy of SE (below 50 eV, dominant for signal) is independent on

2、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 mbarnVHV necessary to keep ionization inside the detector negligible nVery careful insulation and shielding of signal path

3、 to eliminate ionization in air (otherwise nonlinear response)10.6.20083Secondary Emission Monitor working principleSecondary electronsBias E fieldTi Signal electrodeTi HV electrodes Steel vessel (mass) Secondary Electron Emission is a surface phenomenon Energy of SE (below 50 eV, dominant for signa

4、l) 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 mbarIncoming particlenVHV necessary to keep ionization inside the detector negligible nVery careful i

5、nsulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response)10.6.20084Secondary Emission Monitor working principleSecondary electronsBias E fieldTi Signal electrodeTi HV electrodes Steel vessel (mass) Secondary Electron Emission is a surface phenomenon Energy

6、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 mbarIncoming particlenVHV necessary to keep ionization inside t

7、he detector negligible nVery careful insulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response)10.6.20085Secondary Emission Monitor working principleSecondary electronsBias E fieldTi Signal electrodeTi HV electrodes Steel vessel (mass) Secondary Electron Em

8、ission 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 mbarIncoming particlenVHV

9、 necessary to keep ionization inside the detector negligible nVery careful insulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response)10.6.20086Secondary Emission Monitor working principleSecondary electronsBias E fieldTi Signal electrodeTi HV electrodes Ste

10、el 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

11、to signal due to symmetry* 10-4 mbarIncoming particlenVHV necessary to keep ionization inside the detector negligible and avoid capture of electronsnVery careful insulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response)Incoming particle10.6.20087SEM produc

12、tion assemblynAll components chosen according to UHV standardsnSteel/Ti parts vacuum firednDetector contains 170 cm2 of NEG St707 to keep the vacuum 10-4 mbar during 20 yearsnPinch off after vacuum bakeout and NEG activation (p insertion after the bottom is weldednVery high adsorbtion capacity of H2

13、, CO, N2, O2nNot pumping CH4, Ar, He10.6.20088Vacuum bakeout and activation cycle for SEM and BLMInNEG inside the SEM needs additional activation at 350CnActivation means releasing adsorbed gases on the surface which have to be pumpednPinchoff done during the cool down of the chamberVacuum bakeout N

14、EG activation nManifold stays colder to limit the load to the pumping systemnActivation temperature limited by the feedthroughsIon pump started He leak tests He leak tests Vacuum bakeout pinchoff10.6.20089Geant4 simulations of the SEM Secondary Emission Yield is proportional to electronic dE/dx in t

15、he 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 Correction for impact angle included in simulation QGSP_BERT_HP as main physics modelModel calibration factorPenetration distance of SEElec

16、tronic energy lossComparison to literature values = CF = 0.8Geant4 SEM Response function0 impact angle10.6.200810SEM Calibration experiment 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 fil

17、led by AIR measured and simulated as well SEM Response expressed in absolute comparison to Air filled SEM Response = Dose in AIR SEM / output charge of SEM 0.259 +/- 0.016 Gy/count10.6.200811Calibration results050100150200250300350400-0.500.511.52SEM calibration in H4 week 45offset current pASEM ID

18、number024681012141602468SEM calibration in H4, expect from Geant4 3.95+/-0.17ratio QSEM/Qbeam e-/potmonitor positionNot corrected for systematic position errorsOffset current without beamOnly 2 chambers out of 250 had higher offset currentUpper Limit on the SEM pressure: (equivalent to 3 of the hist

19、ogram)1bar(0.6 sigSEM / sigSEM AIR) = 0.26 mbarPressure inside SEMs smaller than this10.6.200812Table of SEM measurements and corresponding simulations10.6.200813Thanks10.6.200814Backup slides Vacuum stand in IHEP for IC production 36 ICs in parallel baked out and filled by N210.6.200815Beam dumped

20、on a Closed Jawof LHC collimator in LSS5. SEM to BLMI comparison 1.3 1013p+Black line signal not clipped 5*_filter = 350msSEMBLMI A10.6.200816Cable crosstalks study important crosstalks caused by long cables in the LSS Ch 6.8 unconnected Xtalk clearly depends on the derivation Signal peak ratio 5e-2

21、 (26dB) (worst case) Integral ratio 4.4e-3 (47dB) Similar behavior for system A X-talks limited to 1 CFC card only!00.10.20.30.40.50.60.7051015Xtalks CD3 - Btime mscounts CH6CH7CH800.10.20.30.40.50.60.7-200204060Differential signals of CD3 - Btime msdifferences counts CH1CH2CH310.6.200817Standard BL

22、MI ARC installationHV Power SupplyHV ground cut hereBLMIUp to 8 BLMs connected in parallelCFC is always close to the quadrupoleSmall low pass filter in the CFC input stage10.6.200818BLMI / SEM installation for collimation areas6 HV capacitors in parallelHV capacitor removed150k for current limitatio

23、n 280pF = chambers capacity 8 chambers in 1 NG18 cable (up to 700m)25pF = SEMs capacity SEM has not 150k protection! 10.6.200819150kOhm 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

24、 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 DC current limited to 1500V / 1Mohm = 1.5 mA Corresponds to 26 Gy/s (total in max 8 chambers)10.6.200820BLMI and SEM in the dump line IR6 on

25、the MKB10.6.200821 Longitudinal 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 wall400 GeV Beam scan in TT20 SPS lineIntegral of Simulation = 0.608 e-mmIntegral of Scan2 = 0.476 e-m

26、mRelative difference22%10.6.200822Prototype 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 underst

27、ood 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 SEY10-310-210-11000.20.250.30.350.4HV kVDetector response charges/p+ C typeF typeGeant410.6.200823Measurements in PS Booster Dump

28、line with 1.4 GeV proton bunches Older prototype measured - Type C 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 00.511.522.5x 101200.01

29、0.020.030.040.050.060.07Beam intensity p+/bunchDetector response charges/p+ DataGeant4.9fit Data10.6.200824Example loss induced by the fast moving SPS scraper. Measured in the collimation area by the LHC BLM system 4 different monitors (2006-old electronics)10.6.200825Example of beam losses in the S

30、PS collimation area during a collimator movement of 10um (2006) Coasting beam2006 dataCWG 19/3/07FFT spectrum10.6.200826SPS Coasting beam 270GeV 200um Left jaw move and FFT spectra10.6.200827Complete FFT from the previous plot Horizontal Tune calculation from the BLM measurement- oscillations in the beam not in the BLM system10.6.200828SEM production assemblynAll components chosen according to UHV standardsnSteel/Ti parts vacuum firednDetector contains 170 cm2 of NEG St