3 PMTs installation All PMTs were taken away for check and reinstalled in the cryostat –New LED on the outer side for better calib. of inner PMTs –Wire alpha sources are at staggered positions Better PMT calibration –Alpha sources (all) on walls were removed 25mm 31mm
4 New LEDs Higher voltage with attenuation by coating LEDS Stable against instability of the input voltage
5 Problem in 2007 Operation Production procedure Fix pins in the holes and fill with silica Bake in argon atmosphere Cool down Metal body Glass insulator Air Xe Watarus Design – Solution for 2007 run No need to change connector Replacement can be done quickly Body made of insulator (not metal)
6 HV Feedthru Modification Test of new feedthru –1000 V applied on all pins (48x6x4 pins) –One feedthru (48 pins) was tested at 1500V Successfully installed welding ceramic Kyocera Ultra High Vacuum Feedthrough New HV feedthru
7 New LN2 feedthru Installation Pressure was slowly increasing under normal operating condition in 2007 runs 6 new LN2 feedthru have been installed –Stainless steel pipes instead of Cu pipes –Pipes are precisely and strongly centered in order not to touch the wall –Bellows connection for the cooling pipes on the covers 30-40W reduction of heat load was achieved But … still pressure is slowly increasing…. !!!!!!!!!! ? Pipes PMTs Cables Refrigerator cooling power: 200W
8 Liquid circulation (Original Design) Circulate xenon in liquid phase –Circulation pump 100liter/h@3175rpm, p = 0.2MPa –Molecular sieves >24 g water absorption Used in 2007 run Temperature Sensor Purifier Cartridge Molecular sieves, 13X 25g water Freq. Inverter OMRON PT
9 Electronegative Impurity Removal (Update in 2008 Run) O 2 getter cartridge –Developed for LAr use at CERN –Mounted at the exit MEG liquid- phase purifier with by-pass valves
10 Liquid-phase Purifier Modification New purifier cartridge to remove water –Oxidization-reduction of Cu –Outside of the purifier cryostat MS is replaced to new pellet –Particle filter has been installed
11 Modification of Splitter-DRS Connections/Cables GND line from splitter floating grounding on DRS board Copper tape + black tape DRS pedestal distribution before/after modification
12 175ns 97ns NaI Electronics Update charge amp. gn0261 (hiroshima-univ.) inverting amp. and timing filter APD Light guide 9 amplifiers prepared, installed all on 17/Jun and checked all signal before connecting to splitter rising time 97ns for fast trigger 225ns (in 2007) ->175ns replaced only amplifiers energy output by new setup 500ns DRS output for trigger output for energy measurement is also faster than that in 2007
13 New Scintillation Counters Used for time calibration of LXe –Scintillator x 2 70mm x 70mm x 7.4mm –Fine mesh PMT x 4 Hamamatsu H6152-70 –Pb converter COBRA NaI
15 Gas/liquid system Gas-phase purifier Liquid- phase purifier Detector 1000 L dewa r High pressur e Storage Gas line Liquid line
16 Scintillation Light Yield In 2007 operation, there was an energy scale discrepancy btw alpha and gamma –Too small light yield from events ( < 1/2) Purity seemed to be good because we observed –Improvement and plateau of light yield of both gammas and alphas but / was found to be smaller than expectation and LP data 2007 Data
17 triplet = 22 ns recomb = 45 ns Waveforms (Shown in 2008 Review) = 21 ns = 34 ns ! Careful treatment of electronics time constant is necessary Xe ee e A Q Q/A Before purification was 1.93+/-0.02 in LP test Electronegative impurity? Oxygen?? 2007 Data
18 Scintillation Light in 2008 Run Rapid increase at the beginning thanks to the liquid-phase purification –Removal of water/oxygen –LN2 cooling was necessary to help limited cooling power during purification Increase (~14%) in summer by gaseous purification, however this was not significant Large increase (46%!) in Oct-Dec after replacing the diaphragm of the gas-circulating pump 205 h 2/Dec 180 h 23/Nov 70 h 14/Nov 2007
19 Why did it change in such way? LN2 cooling pipe –In the cryostat –On the inner vessel wall and covers Diaphragm –found to be broken in September
20 LED Light as a Monitor It is found that our LED system has very good stability. –Much more stable than our calibration precision –We can monitor the stability by a number of PMTs.
21 PMT Gain Shift Gain decrease in pi0 runs PMT gain shift was found with muon beam on ( 2~3% ) –Time constant : short and long –CR peak during MEG run –LED run with normal muon beam –LED constant intensity with open/close beam blocker Beam on Beam off
22 Hamamatsu Investigation Too much alkali ?????
23 Yet Another Way to Monitor the Light (Cosmic ray) Am-Be alpha source
25 Work during the shutdown PMT/Cryostat –Open the downstream cryostat cover –Visual inspection of the cryostat –Take a few PMT to be sent back to Hamamatsu for further investigation of gain change –Installation of a new chimney cover with steel cooling pipe (previous one was made of Cu) Replacement of the 1000L dewar heater –Recovery of xenon to the storage in Feb –Replacement of the heater and warm up frozen xenon in Mar –Liquefaction in April Installation of new getter in March on the top of the cryostat Installation of new Liquid Pump/Purifier in April –1000 L/hour circulation expected –No electric noise
26 Liquid filling schedule Detector –6-19/April Evacuation –20-22/April pre-cooling –23-24/April cold gas alpha DAQ –25-26/April Liquid transfer –27/April-10/May Electronics test Purifier test –11/May- Purification and test 1000L dewar –26/Jan-27/Feb Recovery of xenon to the storage –2/Mar-6/Mar Recovery of the gas in the dewar –9/Mar-13/Mar Repair work of the heater –14/Mar-1/April Evacuation –2/April-22/April Liquefaction –Complete removal of impurities
Summary Successful running in 2008 –Remaining problems Scintillation light yield (30% less than LP data) Cooling power Hardware upgrade/repair –New Getter purifier –New liquid pump –Replacement of the top chimney cover LN2 cooling pipe: Cu Stainless Steel –Replacement of the heater in the 1000L dewar PMT gain shift investigation is in progress by Hamamatsu Detector will be ready in the middle of May
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