1. Xenon Detector Status Liquid Xenon Group

2. 1 Outline Detector Setup Operation Performance Problems and solutions

3. Detector Setup

4. 3 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

5. 4 Sensors, LEDs, and alpha sources Two type of  sources Plate 20 pieces Wire 5x5 wires LED 3 different attenuation x 10 Pt100 Temp sensor 22 sensors in LXe 21 sensors on the wall Capacitor-type surface level meter

6. 5 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. 6 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 outgas Xe leak Warm vessel vacuum ~1 bar xenon vacuum Mass spectrometer

8. 7 RGA of leaking xenon Doubly charged 132 Xe (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. 8 Closing the covers Gaskets replaced with newly delivered ones on 5/Sep Super-insulator on the cold vessel 240 Nmm torque

10. 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 –Doubly charged 132 Xe (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. 10 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. 12 Gas/liquid system Gas-phase purifier Liquid- phase purifier Detector 1000 L dewa r High pressur e Storage Gas line Liquid line

14. 13 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) 0.133 MPa 0.11 MPa Xenon gas Cryo pump

15. 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 0.25 MPa Xenon liquid 0.11 MPa ~3m

16. 15 End of xenon filling temperature Level meter Additional 10 liter was transferred for assurance

17. 16 How many liters of liquid xenon? Cryostat volume1200 liter PMT and support142 + 43 = 185 liter Filler135 liter –Lateral96 liter –Bottom39 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. 17 Slow Control Detector, storage, dewar, purifiers MEG Central DAQ System (SCFE) For shift crew use Labview megon00PC in barrack XEC PC 2 For expert use Labview XEC PC 1 XEC dedicated SCFE Node cooperation Alarm to experts Important controls are implemented in SCS nodes

19. 18 Liquid circulation Circulate xenon in liquid phase –Circulation pump 100liter/h@3175rpm,  p = 0.2MPa –Molecular sieves >24 g water absorption Temperature Sensor Purifier Cartridge Molecular sieves, 13X 25g water Freq. Inverter OMRON PT

20. 19 Succeeded! 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 50.63Hz ! Circulation period

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

22. 21 Absorption Length Ratio Data/MC vs distance fitted with an exponential curve.Ratio Data/MC vs distance fitted with an exponential curve. Inner and Outer face PMTsInner and Outer face PMTs Cosine of incidence angle < -0.2Cosine of incidence angle < -0.2 Slope compatible with zero (no absorption).Slope compatible with zero (no absorption). > 3 m @95 % C.L. > 3 m @95 % C.L. PMT Alpha source After 50 h purification, 4/Nov

23. Performance 2D display, charge/time2D hist, charge:PMT#3D reconstructed position Waveform1D histogramsCharge:event#

24. 23 PMT Calibration PMT calibration –LED PMT gain –Flushing LEDs at different intensities –N pe ~1/  2 Time offset calibration –Viewing one LED flushing with many PMTs simultaneously –Alpha QE and absorption length evaluation Liquid and cold gas

25. 24 Time offset determination Possible method only in non-segmented detector like ours c’ is obtained by using all data TjTj l i,j -l i-1,j 1/c’ t i –t i-1 Measured Flashing Time Of i-th LED Speed of LED light Offset of j-th PMT Different LEDs viewed by one PMT RD run (ultra low) t xe - t TC

26. 25 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. 26 CEX run - Pi0 calibration CEX process –  - p   0 n  0 (28MeV/c)   54.9 MeV < E(  ) < 82.9 MeV LH 2 target 00     54.9MeV 82.9MeV 1.3MeV for  >170 o 0.3MeV for  >175 o   170 o 175 o  NaI tagging counter –3x3 crystals, APD readout Pb collimator panel in front of the Xe detector

28. 27 LH 2 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. 28 NaI Detector beam axis +/- 21 (+/- 0.07) deg. Up/down +/- 60 (+/- 0.005) deg.

30. 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  up = 2.4% FWHM = 6.5% pedestal 55MeV gamma

31. 30 Time Measurement Using only 12 PMTs around the center T : weighted mean of inner PMT timing after subtracting photon propagation time Effective velocity 10cm/ns Practical resolution by t Xe – t sci 280ps 115ps Intrinsic resolution by T-B analsysis

32. 31 Position Measurement Using collimator run data,

33. 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

34. Problems found in 2007 and solutions for 2008 run

35. 34 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. 35 How did we make new ones? Production procedure Fix pins in the holes and fill with silica Bake in argon atmosphere Cool down Metal body Glass insulator Air Xe Wataru’s Design No need to change connector Replacement can be done quickly Body made of insulator (not metal)

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

38. 37 PMT status after replacing feedthru Stable operation after replacing feedthru LED intensity optimization –Better gain evaluation than before

39. 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 –1 st experience of temperature cycle –Test of the gasket –RGA: I = 3.8x10 -13 A  5.7x10 -7 mbarl/sec 132 Xe ++

40. 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 welding ceramic Kyocera Ultra High Vacuum Feedthrough

41. 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) 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? ? Pipes PMTs Cables

42. 41 LN2 cooling pipe Cu pipe feedthru  SUS pipe feedthru

43. 42 Cooling Power

44. 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 PT O-ring collar Cup nut Plug or shaft Wilson Seal Air xenon bellows Liquid xenon

45. 44 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 Trigger PMT splitter

46. 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 

47. 46  triplet = 22 ns  recomb = 45 ns Waveforms     = 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??

48. 47 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. 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 –LN 2 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