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Xenon Detector Status

Xenon Detector Status. Liquid Xenon Group. Outline. Detector Setup Operation Performance Problems and solutions. Detector Setup. PMT installation completed. All PMT successfully installed in Aug 2007 together with LEDs Alpha sources (plates and wires) PT100 temperature sensors

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Xenon Detector Status

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  1. Xenon Detector Status Liquid Xenon Group

  2. Outline • Detector Setup • Operation • Performance • Problems and solutions

  3. Detector Setup

  4. PMT installation completed • All PMT successfully installed in Aug 2007 together with • LEDs • Alpha sources (plates and wires) • PT100 temperature sensors • Laser fibers • Surface level meter • < 200~300um gap btw inner slab and wall xenon g

  5. Sensors, LEDs, and alpha sources Capacitor-type surface level meter Pt100 Temp sensor 22 sensors in LXe 21 sensors on the wall • Two type of a sources • Plate 20 pieces • Wire 5x5 wires LED 3 different attenuation x 10

  6. Cabling and Al filler installation • 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) 7.5l 4.5l

  7. We were ready to close but… • The shape of the newly delivered sealing (metal gasket) was wrong ! • Does not fit the groove?! • Radii were correct but they made a mistake in bending • Sent back to Garlok and repaired • While waiting repair work, old gaskets were recycled with indium foil around the corner • Vacuum test OK • But leak of the order of 10-4 mbarl/sec with ~1 bar xenon in the cold vessel ~1 bar xenon outgas vacuum Warm vessel vacuum Xe leak Mass spectrometer

  8. 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

  9. Closing the covers • Gaskets replaced with newly delivered ones on 5/Sep • Super-insulator on the cold vessel • 240 Nmm torque

  10. 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 • 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 10-4 mbarl/sec leak

  11. Estimation of xenon leak rate Recycled gasket 10-4 mbarl/sec leak Room temperature xenon gas New gasket Room temperature xenon gas Better at low temperature

  12. Operation

  13. Gas/liquid system Gas-phase purifier Gas line Liquid line High pressure Storage Detector 1000L dewar Liquid-phase purifier

  14. Evacuation and liquefaction • Evacuation started on 5/Sep • Thanks to cryo pump (AISIN) • 6.9x10-3 Pa in 3 days • Cooling started on 10/Sep • Liquefaction started on 15/Sep • Surface level was monitored with • Temperature sensors • Level meter (long and short) Cryo pump Xenon gas 0.11 MPa 0.133 MPa

  15. Xenon liquid 0.25 MPa 0.11 MPa 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 ~3m

  16. End of xenon filling • Additional 10 liter was transferred for assurance temperature Level meter

  17. How many liters of liquid xenon? • Cryostat volume 1200 liter • PMT and support 142 + 43 = 185 liter • Filler 135 liter • Lateral 96 liter • Bottom 39 liter • Cable 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

  18. Labview Slow Control megon00 PC in barrack MEG Central DAQ System (SCFE) For shift crew use Labview 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

  19. Temperature Sensor Liquid circulation Purifier Cartridge Molecular sieves, 13X 25g water Freq. Inverter OMRON • Circulate xenon in liquid phase • Circulation pump • 100liter/h@3175rpm, Dp = 0.2MPa • Molecular sieves • >24 g water absorption PT

  20. 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

  21. 205 h 2/Dec 180 h 23/Nov 70 h 14/Nov Liquid-phase purification • Light yield for 17.6MeV g 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 problem (reported later) • Noise from the pump (freq. inverter?) affected other detectors C-W run 17.6MeV gamma

  22. Absorption Length • 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). l> 3 m @95 % C.L. After 50 h purification, 4/Nov Alpha source PMT

  23. 2D display, charge/time 2D hist, charge:PMT# 3D reconstructed position Performance Waveform 1D histograms Charge:event#

  24. PMT Calibration • PMT calibration • LED • PMT gain • Flushing LEDs at different intensities • Npe~1/s2 • Time offset calibration • Viewing one LED flushing with many PMTs simultaneously • Alpha • QE and absorption length evaluation • Liquid and cold gas

  25. Time offset determination • Possible method only in non-segmented detector like ours • c’ is obtained by using all data Different LEDs viewed by one PMT Measured Flashing Time Of i-th LED Speed of LED light Offset of j-th PMT Tj RD run (ultra low) ti –ti-1 1/c’ txe - tTC li,j-li-1,j

  26. C-W run • Li at 14.6, 17.6 MeV • B at 4.4, 11.7 and 16.1 MeV • Details in Giovanni’s presentation

  27. CEX process p-pp0n p0(28MeV/c)  g g 54.9 MeV < E(g) < 82.9 MeV LH2 target NaI tagging counter 3x3 crystals, APD readout Pb collimator panel in front of the Xe detector Eg 170o q Eg Eg p0 175o q 54.9MeV 82.9MeV 1.3MeV for q>170o 0.3MeV for q>175o Eg CEX run - Pi0 calibration g

  28. 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

  29. NaI Detector beam axis+/- 21 (+/- 0.07) deg. Up/down+/- 60 (+/- 0.005) deg.

  30. 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 sup = 2.4% FWHM = 6.5%

  31. Practical resolution by tXe – tsci 280ps Time Measurement Intrinsic resolution by T-B analsysis • Using only 12 PMTs around the center 115ps • T : weighted mean of inner PMT timing after subtracting photon propagation time • Effective velocity 10cm/ns

  32. Position Measurement • Using collimator run data,

  33. 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

  34. Problems found in 2007andsolutions for 2008 run

  35. 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?

  36. How did we make new ones? Wataru’s 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)

  37. 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 alpha DAQ • 21, 22, 23/Oct transfer speed 15~20 liter/hour • Completed early morning of 24/Oct • 2 weeks interruption of DAQ

  38. PMT status after replacing feedthru • Stable operation after replacing feedthru • LED intensity optimization • Better gain evaluation than before

  39. 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 132Xe++

  40. 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

  41. PMTs ? Cables Pipes 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) • Heat income through Cu cooling pipes was not taken into account • 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 • There seems to be other heat leak… • Larger than 50W • Super-insulator?

  42. LN2 cooling pipe • Cu pipe feedthru  SUS pipe feedthru

  43. Cooling Power

  44. PT 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 Cup nut collar bellows O-ring Liquid xenon

  45. PMT Signal Splitter • Spark in feedthru’s 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 DRS splitter PMT Trigger

  46. Light YieldDiscrepancy between a and g data • Energy scale discrepancy btw alpha and gamma • Too small light yield from g 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 a

  47. g a e Xe Xe e e Xe Xe Waveforms • triplet= 22 ns • recomb= 45 ns tg = 34 ns ta = 21 ns ! Careful treatment of electronics time constant is necessary Before purification Q/A was 1.93+/-0.02 in LP test A Q Electronegative impurity? Oxygen??

  48. Electronegative Impurity Removal • O2 getter cartridge • Developed for LAr use at CERN • be mounted at the exit MEG liquid-phase purifier with by-pass valves • Preparing an oxygen purity monitor also • will be ready at an early stage of 2008 run

  49. 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 of March • Evacuation, liquid transfer, purification • Ready on 19/April • Schedule at http://meg.web.psi.ch/subprojects/install/xenon.html

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