Secondary Emission Monitor working principle二次发射显示器的工作原理

1、secondary emission monitorfor very high radiation areas of lhcdaniel kramer for the blm teamsecondary electronsbias e fieldti signal electrodeti hv electrodes steel vessel (mass)nsecondary electron emission is a surface phenomenon nenergy of se (below 50 ev, dominant for signal) is independent on pr

2、imary energynse are pulled away by hv bias field (1.5kv)nsignal created by e- drifting between the electrodes ndelta 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)secondary electronsbias e fieldti signal electrodeti hv electrodes steel vessel (mass)nsecondary electron emission is a surface phenomenon nenergy of se (below 50 ev, dominant for signal) is independent on primary energynse are pulled away

4、 by hv bias field (1.5kv)nsignal created by e- drifting between the electrodes ndelta electrons do not contribute to signal due to symmetry* 10-4 mbarincoming particlenvhv necessary to keep ionization inside the detector negligible nvery careful insulation and shielding of signal path to eliminate i

5、onization in air (otherwise nonlinear response)secondary electronsbias e fieldti signal electrodeti hv electrodes steel vessel (mass)nsecondary electron emission is a surface phenomenon nenergy of se (below 50 ev, dominant for signal) is independent on primary energynse are pulled away by hv bias fi

6、eld (1.5kv)nsignal created by e- drifting between the electrodes ndelta electrons do not contribute to signal due to symmetry* 10-4 mbarincoming particlenvhv necessary to keep ionization inside the detector negligible nvery careful insulation and shielding of signal path to eliminate ionization in a

7、ir (otherwise nonlinear response)secondary electronsbias e fieldti signal electrodeti hv electrodes steel vessel (mass)nsecondary electron emission is a surface phenomenon nenergy of se (below 50 ev, dominant for signal) is independent on primary energynse are pulled away by hv bias field (1.5kv)nsi

8、gnal created by e- drifting between the electrodes ndelta electrons do not contribute to signal due to symmetry* 10-4 mbarincoming particlenvhv necessary to keep ionization inside the detector negligible nvery careful insulation and shielding of signal path to eliminate ionization in air (otherwise

9、nonlinear response)secondary electronsbias e fieldti signal electrodeti hv electrodes steel vessel (mass)nsecondary electron emission is a surface phenomenon nenergy of se (below 50 ev, dominant for signal) is independent on primary energynse are pulled away by hv bias field (1.5kv) transit time 500

10、psnsignal created by e- drifting between the electrodes ndelta electrons do not contribute 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 elim

11、inate ionization in air (otherwise nonlinear response)incoming particlenall 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 afte

12、r the bottom is weldednvery high adsorbtion capacity of h2, co, n2, o2nnot pumping ch4, ar, henneg 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 neg a

13、ctivation 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 pinchoffmodel calibration factorpenetration distance of seelectronic energy losscomparison to literature values = cf

14、= 0.8geant4 sem response function0 impact angle050100150200250300350400-0.500.511.52sem calibration in h4 week 45offset current pasem id number024681012141602468sem calibration in h4, expect from geant4 3.95+/-0.17ratio qsem/qbeam e-/potmonitor positionnot corrected for systematic position errorsoff

15、set current without beamonly 2 chambers out of 250 had higher offset currentupper limit on the sem pressure: (equivalent to 3 of the histogram)1bar(0.6 sigsem / sigsem air) = 0.26 mbarpressure inside sems smaller than thisblack line signal not clipped 5*_filter = 350mssemblmi a00.10.20.30.40.50.60.7

16、051015xtalks cd3 - btime mscounts ch6ch7ch800.10.20.30.40.50.60.7-200204060differential signals of cd3 - btime msdifferences counts ch1ch2ch3hv power supplyhv ground cut hereblmiup to 8 blms connected in parallelcfc is always close to the quadrupolesmall low pass filter in the cfc input stage6 hv ca

17、pacitors in parallelhv capacitor removed150k for current limitation 280pf = chambers capacity 8 chambers in 1 ng18 cable (up to 700m)25pf = sems capacity sem has not 150k protection! integral of simulation = 0.608 e-mmintegral of scan2 = 0.476 e-mmrelative difference22%psi proton beam 62.9mev blms prototypes f & c type hv dep