Xenon Detector Status Liquid Xenon Group Outline Detector Setup Operation Performance Problems and solutions 2 Detector Setup PMT installation completed All PMT successfully installed i n Aug 2007 together with
LEDs Alpha sources (plates and wires) PT100 temperature sensors Laser fibers Surface level meter < 200~300um gap btw inner sl ab and wall xenon 4 Sensors, LEDs, and alpha sources Capacitor-type surface level meter Pt100 Temp sensor
22 sensors i n LXe 21 sensors on the wall Two type of sources Plate 20 pieces Wire 5x5 wires LED 3 different attenuation x 10 5 Cabling and Al filler installation 7.5l 4.5l Filler volume Lateral 7.5lx6x2 + 4.5lx2x2 = 108l (design) 108 7.5(US) 4.5(DS) = 96l
(reality) Bottom 49l (design) 49 10 = 39l (reality) 6 We were ready to close but The shape of the newly delivered sealin g (metal gasket) was wrong ! Does not fit the groove?! Radii were correct but they made a mist ake in bending Sent back to Garlok and repaired While waiting repair work, old gaskets w ere recycled with indium foil around the corner Vacuum test OK But leak of the order of 10-4 mbarl/sec wi th ~1 bar xenon in the cold vessel
outgas ~1 bar xenon vacuum Warm vessel vacuum Xe leak Mass spectrometer 7 RGA of leaking xenon Doubly charged 132Xe (Xe++) is used to evaluate amount of xenon in the warm vessel Production cross section with 110keV electron is ~40% of Xe+ production
Used as reference data for later use 10-4 mbarl/sec leak 8 Closing the covers Gaskets replaced with newly delivered ones on 5/Sep Super-insulator on the cold vessel 240 Nmm torque 9 Pressure/leak test Xenon gas (liquid) in the cold vessel Mass spectrometer on the warm vessel
RGA data with recycled gasket used as a reference 10-4 mbarl/sec leak Doubly charged 132Xe (Xe++) is used to evaluate amount of xenon in the warm vessel Production cross section with 110keV electron is ~40% of Xe+ production 10 Estimation of xenon leak rate 10 Recycled gasket 10-4 mbarl/sec leak Room temperature xenon gas y =10.9x - 0.3403 R2 =0.9825
Peak Ion current at A= 66 [x10^ -10 A] 1 0.1 New gasket 0.01 0.001 0.06 Room temperature xenon gas 0.07 0.08 0.09
0.1 0.11 0.12 Xenon Gas Pressure [MPa] y =0.1187x - 0.0083 R2 =0.9617 0.13 0.14 0.15 0.16 Better at low temperature 11 Operation Gas/liquid system Gas-phase
purifier Gas line Liquid line Detector 1000 L dewa r Liquidphase purifier High pressur e Storage 13 Evacuation and liquefaction Evacuation started on 5/Sep Thanks to cryo pump (AISIN)
6.9x10-3 Pa in 3 days Cryo pump Cooling started on 10/Sep Liquefaction started on 15/Sep 0.133 M Pa Xenon gas 0.11 MPa Surface level was monitored with Temperature sensors Level meter (long and short) 14 Liquid transfer
Liquid transfer by pressure difference between two cryostats through a vacuum insulated pipe Started on 17/Sep and completed on 20/Sep 10 liter/hour transfer speed Xenon filling was done in 15 days after starting evacuation Xenon liquid ~3m 0.25 MPa 0.11 MPa 15 End of xenon filling temperature Level
meter Additional 10 liter was transferred for assurance 16 How many liters of liquid xenon? Cryostat volume 1200 liter PMT and support 142 + 43 = 185 liter Filler 135 liter Lateral Bottom Cable 96 liter 39 liter 20~30 liter Additionally transferred amount of xenon
~10 liter 1200 185 135 25 + 10 = 865 liter Consistent with remaining amount of xenon in the dewar 17 Labview Slow Control megon00 PC in barrack MEG Central DAQ System For shift crew use Labview (SCFE)
XEC PC 2 XEC dedicated SCFE Node cooperation Alarm to experts XEC PC 1 For expert use Important controls are implemented in SCS nodes Detector, storage, dewar, purifiers 18 Liquid circulation Circulate xenon in liquid phase Circulation pump 100liter/[email protected], p = 0.2MPa
Molecular sieves Purifier Cartridge Molecular sieves, 13X 25g water Freq. Inverter OMRON PT >24 g water absorption Temperature Sensor 19 Succeeded! Circulation period
50.63Hz ! Circulation speed evaluation change of the surface level after closing the inlet valve 3.6% / 30sec ~ 432% / h 1% corresponds to 0.165 liter 0.165x 432%/h = 71 liter /hour 20 Liquid-phase purification Light yield for 17.6MeV saturated around 23/Nov (180h purification time) Necessary to continue longer than we expected 5 hours purification was enough in the LP test (100L LXe) Probably due to slower circulation speed (100L/h 70L/h) Worse initial condition compared to the LP
Needed longer time to prepare monitoring tools due to PMT HV feedthru pro blem (reported later) Noise from the pump (freq. inverter?) affected other detectors C-W run 17.6MeV gamma 180 h 205 h 23/Nov 2/Dec 70 h 14/Nov 21 Absorption Length
> 3 m @95 % C.L. Ratio Data/MC vs distance fitted with an exponential curve. Inner and Outer face PMTs Cosine of incidence angle < -0.2 Slope compatible with zero (no absorption).
After 50 h purification, 4/Nov n Alpha source PMT 22 2D display, charge/time 2D hist, charge:PMT# 3D reconstructed position Performance Waveform 1D histograms Charge:event# PMT Calibration PMT calibration
LED PMT gain Flushing LEDs at different intensities Npe~1/2 Time offset calibration Viewing one LED flushing with many PMTs simultan eously Alpha QE and absorption length e valuation Liquid and cold gas 24 Time offset determination Possible method only in non-segmented detector like ours
c is obtained by using all data T j ti Measured Flashing Time Of li , j c' Dj Different LEDs viewed by one PMT Speed of LED light Offset of j-th PMT i-th LED
Tj RD run (ultra low) ti ti-1 1/c li,j-li-1,j txe - tTC 25 C-W run Li at 14.6, 17.6 MeV B at 4.4, 11.7 and 16.1 MeV Details in Giovannis presentation 26
CEX run - Pi0 calibration CEX process 54.9MeV p n - 82.9MeV 0 170o 0(28MeV/c) 54.9 MeV < E() < 82.9 MeV
175o 0 1.3MeV for >170o 0.3MeV for >175o NaI tagging counter 3x3 crystals, APD readout
LH2 target Pb collimator panel in front of the Xe detector 27 LH2 Target Pressure test of cell 4.5 bar (abs) Time to liquefy 80 min from start of LHe flow Liquid stability 1.2 bar operating pressure (96% cell full) 1.3% RMS, 6% max excursion Liquid Helium consumption
2.4%/h 42h auto 28 bea +/- m ax deg 21 (+ is /- 0 . .0 7) NaI Detector Up/down +/- 60 (+/- 0.005) deg. 29 CEX run data analysis, preliminary
Position cut Cut shallow events (< 2cm) Select only center events ( |u|,|v| < 5cm) Position correction Pile-up rejection by light distribution Select center event on NaI detector Not applied QE correction If applied worsen resolution. Pedestal has 2% spread Needs better baseline evaluation Check hardware for 2008 run 55MeV gamma pedestal up = 2.4%
FWHM = 6.5% 30 Time Measurement Using only 12 PMTs around the center Intrinsic resolution by T-B analsysis 115ps Practical resolution by tXe tsci 280ps T : weighted mean of inner PMT timing after subtracting photon propagation time
Effective velocity 10cm/ns 31 Position Measurement Using collimator run data, 32 Physics run RD run gamma energy Data : Xe self trigger threshold=3.5V MC : RD event generation + event overlaps + trigger simulation Vertical scale is scaled assuming, Mu stop = 5e6 Calorimeter acceptance = 0.1 Calorimeter detection efficiency = 0.6 33
Problems found in 2007 and solutions for 2008 run Feedthru We could not apply required voltage on all PMTs at the beginning We found that this had been caused by spark in the feedthru Needed to prepare new ones for 2007 run Commercial products or hand made? 35 How did we make new ones? Watarus Design Air Metal body Glass
insulator Xe Production procedure Fix pins in the holes and fill with silica Bake in argon atmosphere Cool down No need to change connector Replacement can be done quickly Body made of insulator (not metal) 36 Installation Oct. 10-12: LXe recovery to 1000L Dewar Oct. 13-14: GXe recovery
Oct. 15-16: Mounting new flanges & testing With flushing dry nitrogen gas in the cryostat Oct 17-19: evacuation Gas filling ~0.13MPa Successfully took gas alpha data at 800, 900, 1000V LED data Liquid transfer started at almost same time
Until the detector is cooled we continued LED and alp ha DAQ 21, 22, 23/Oct transfer speed 15~20 liter/h our Completed early morning of 24/Oct 2 weeks interruption of DAQ 37 PMT status after replacing feedthru Stable operation after repl acing feedthru LED intensity optimization Better gain evaluation than before 38
As a bonus Xenon recovered through purifier Practice to transfer the liquid to the dewar Water contamination suppressed Cryostat was warmed up to ~220K 1st experience of temperature cycle Test of the gasket RGA: I = 3.8x10-13A 5.7x10-7 mbarl/sec 132 Xe++ 39 Future plan (currently ongoing) Replacement during
winter shutdown 48 pin x 6 x 4 Need to change connectors Used in the small prototype and PMT test chamber ceramic Kyocera Ultra High Vacuum Feedthrough welding 40 Heat load Pressure is slowly increasing under normal operating condition. Refrigerator cooling power: 200W Expected redundant cooling power: ~100W
Calculation based on LP modeling PMT:37W (Vmean = 775V) Conduction:64W ? Cable (50), Chimney (4.8), SI(3.1), Support(6.3) Cu heat conduction: 390 W/m/K 10mm diam 1mmt pipe, 20cm 390 x 135 (K) x 2.83x10-5/0.2 (m) = 7.4W 6 pipes 44.4W
Cf. Steel heat conduction ~20W/m/K PMTs Cables Heat income through Cu cooling pipes was not taken into account PMT Cable Chimney Radiation Support Cu pipe ? Pipes There seems to be other heat leak
Larger than 50W Super-insulator? 41 LN2 cooling pipe Cu pipe feedthru SUS pipe feedthru 42 Cooling Power PC150 Cooling power at PSI - 24 Aug.,2007 LYBOLDT6000 6.5kW at 50Hz Orifice: 35 77.5K 0W 123K 100W 143K 150W 155K 180W Vac: ~10-2 Pa
100 120 140 160 180 Temperature (K) 43 Blow up of low temperature valve Low temperature valves blew up A few liters of liquid xenon was lost Purifier cryostat was opened
Misleading valve design No documentation on the manual Piping was modified and no valve is in use now Wilson Seal Air Wilson Seal xenon Plug or shaft PT Cup nut collar bellows O-ring
Liquid xenon 44 PMT Signal Splitter Spark in feedthrus destroyed protection zener diodes on PMT splitter boards base-line shift at splitter output Signal was out of range of WFD Fixed by replacing all zener diodes splitter DRS PMT
Trigger 45 Light Yield Discrepancy between and data Energy scale discrepancy btw alpha and gamma Too small light yield from events (~1/2) Not due to magnetic field Confirmed by taking C-W data w/o COBRA field Purity seems good Improvement and plateau of light yield of both gammas and alphas Have a look on WF 46 Waveforms triplet= 22 ns recomb= 45 ns
= 34 ns = 21 ns e X X eX eX e e e ! Careful treatment of electronics time constant is necessary e X eX e
e e X eX e e Before purification Q/A Q / A Q / A 1.25 0.02 was 1.93+/-0.02 in LP test A Q
Electronegative impurity? Oxygen?? 47 Electronegative Impurity Removal O2 getter cartridge Developed for LAr use at CERN be mounted at the exit MEG liquid-phase p urifier with by-pass valves Preparing an oxygen purity monitor also will be ready at an early stage of 2008 run 48 Current Status and Schedule Xenon recovered to the 1000 liter dewar Gas analysis will be done on site Cryostat is opened now All PMTs and cables are checked Replacing feedthru is in progress LN2 cooling pipe modification
Cryostat will be moved back to PiE5 at the end o f March Evacuation, liquid transfer, purification Ready on 19/April Schedule at http://meg.web.psi.ch/subprojects/install/ xenon.html 49
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