HCAL 137 Cs calibration 18-19/11/2014 3Yu. Guz 2014/11/26 The 137 Cs sources installed into HCAL on 03/11/2014; The calibration performed 18-19/03/2014 (two runs) Two goals produce new HV, after 2 years and 193 PMT replacements (121 new PMTs) ==> quite significant HV changes expected one source passage, i.e. assumed α unchanged (G=G 0 ·HV α ) a new PHYSICS recipe created (preliminary) test linux version of the calibration s/w (Vasily Kudryavtsev, BINP) one source passage at side C; minor problems found Need 1-2 runs more finalize the linux version perform 3 source passages at different HV, in order to determine both G 0 and α
ECAL 4Yu. Guz 2014/11/26 Few dead cells appeared after closing the detector (one of them makes the whole power line, 20 PMTs, not working). There will be a chance to access, in a shadow of MUON work.
HCAL PMT problem – follow-up 5Yu. Guz 2014/11/26 Found by HAMAMATSU experts: the vacuum inside the PMT bulb is not degraded, no micro cracks in glass the problems (dark current etc) are caused by migration of alcali inside the bulb one PMT had been baked for 1.5 hour at 125 o C – the behavior improved significantly however the HAMAMATSU experts do not expect the improvement to be stable for long term The differences in PMT operation conditions between HCAL and ECAL: higher voltage: 900 – 1300 V in HCAL vs 600 – 900 V in ECAL (max 1800 V according to the datasheet) electrostatic: the magnetic shielding in HCAL is grounded black paint applied to HCAL PMTs for light tightness (may contribute to electrostatic conditions) some mechanical stress in HCAL PMTS (can lead to micro cracks and degradation of vacuum – discarded by HAMAMATSU studies, see below) From HAMAMATSU: light emission shows the place where dark current occurs
6Yu. Guz 2014/11/26 While the way of degradation was found (migration of alcalis within PMT bulb), the reason why it happens in ECAL and not in ECAL is unclear. We can only make hypotheses. The differences in the HCAL/ECAL operating conditions which can be relevant are only somewhat higher voltage (900 – 1300 vs 600 – 900) in combination with electrostatic conditions (grounded bulb) The limit operating voltage for this type of PMTs is 1800 V according to the specs, it is not exceeded. However an additional factor leading to the decrease of allowed voltages can be the special treatment of the dynode system, which HAMAMATSU made for us in order to decrease the rate effect When purchasing additional PMTs from HAMAMATSU, we can think of asking them to produce (a significant part of) PMTs without such treatment. The rate effect will of course become larger; however it will be mitigated by the 11 kHz LED pulsing. It can be a good compromise for (most of) HCAL, where the requirements are not very tight (5% will be good enough) – of course if the guess is right and PMTs without treatment will not experience such degradation We can also try to modify the electrostatic conditions in HCAL, by, e.g., wrapping the µ-metal shield with kapton tape In the meanwhile, we can bake the bad PMTs (we have ~150 for the moment) and see whether it will help; however HAMAMATSU experts do not expect steady improvement HCAL PMT problem – follow-up
7 CALO operation at high lumi (slides from 2012)
82012-12-12Yu. Guz high lumi test HCAL PMT anode currents at 10 33. Factor of 2.5 wrt normal operation @ 4·10 32. The current is up to 50 µA (max 100 µA according to the datasheet) The system of measurement of current is close to limit at the 4 central counters 04/12/2012 L=10 33
92012-12-12Yu. Guz ECAL PMT anode currents at 10 33. Factor of 2.5 wrt normal operation @ 4·10 32. Sensitivity is ~ 100 DCU counts per 1 µA (current up to 10 – 12 µA ) high lumi test 04/12/2012
102012-12-12Yu. Guz MV currents in HCAL and ECAL – only slight increase compared to normal. high lumi test 04/12/2012
112012-12-12Yu. Guz high lumi test hctell04 & hctell05pstell03 & pstell06 30/11/2012, run 133451, L=6·10 32 Stephane T. few TELL1s close to the bandwidth limit
Yu. Guz 2014/02/1912 The PMTs in HCAL and ECAL centre will not exceed the max allowed DC anode current The TELL1s system, after the recent modifications, will not saturate The radiation damage Probably after Run II at high lumi (10 fb -1 ) we will have to replace inner ECAL modules already in LS2 Also some CW boards in ECAL central cells will have to be replaced, maybe during Christmas shutdowns HCAL central cells degradation – consequences for trigger? (most probably not severe) CALO operation at higher lumi in Run II
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