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  • Slide 1
  • Xenon Detector Status Liquid Xenon Detector Group
  • Slide 2
  • Contents PMT R&D New PMT with double Al strip New base design with zener diodes PMT response under the COBRA field Neutron BG measurement Previous talk Cryostat/PMT holder design Calibration/Monitoring Another CEX beam test at E5 Schedule
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  • PMT R&D Photocathode New breeder circuit with zener diodes Test under the COBRA magnetic field
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  • Motivation Under high rate background, PMT output (old Type PMT, R6041Q) reduced by 10-20%. This output deterioration has a time constant (order of 10min.): Related to the characteristics of photocathode whose surface resistance increases at low temperature. Rb-Sc-Sb + Mn layer used in R6041Q Not easy to obtain high gain. Need more alkali for higher gain. Larger fraction of alkali changes the characteristic of PC at low temp. So, New Type PMTs, R9288 (TB series) were tested under high rate background environment. K-Sc-Sb + Al strip used in R9288 Al strip, instead of Mn layer, to fit with the dynode pattern Confirmed stable output. ( Reported in last BVR) But slight reduction of output in very high rate BG Add more Al Strip Al Strip Pattern Low surface resistance R9288 ZA series Yasuko HISAMATSUMEG VRVS Meeting @PSI June 2004
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  • R6041Q (Rb-Sc-Sb w/o Al strip used in LP) Serial # Beam on 83MeV 55MeV Lab test Test LED with crowing LED (0.8 microA) -105 o C25 o C Only base current shortage effect
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  • Works on Design of PMT Two Issues to be solved: 1.Output deterioration caused by high rate background. (Effects of ambient temperature on Photocathode ) Ans. Reduce Surface Resistance by adding Aluminum Strip Pattern 2. Shortage of Bleeder Circuit Current Ans. Improve Design of the Circuit by adding Zener Diode Delivered from HPK in April Rate Dependence Test @ Liq.Xe HPK has started to work on new bleeder circuit design Yasuko HISAMATSUMEG VRVS Meeting @PSI June 2004
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  • PMT test facility in Pisa Is operating stabily and allows to test PMTs in Lxe with Alpha sources (QE) LEDs (high rate test) Laser light through fiber (stability) Compare each PMT to a reference PMT Reference PMT fixed. Change test PMT.
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  • PMT fast change mode successfully tested Linear motion to dip PMTs Gate valve to isolate N 2 /Xe Allows to test several PMTs/day (5) Alpha-source signal Anticorrelation in liquid not seen in gas Purity of Xe? checking Upper Lower SUM
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  • High rate tests In parallel with -source/purity tests Check on Double-Al-Grid PMTs (unfortunately only 2 samples) NO effect seen at 4 A anodic current at -109C (1 Atm) Note: usually Xe kept at -105, 1.3 Atm ZA1985 ZA1980 Crowding ON OFF
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  • I=4 A TB604 ZA1985 ZA1980 Plateau/Peak New 9288 (ZA1980 and ZA1985) compared to TB604 (in Ar gas and LXe)
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  • PMT Rate Dependence Test in Tokyo Xe tank Liq.Xe chamber Purification system PMT Test facility @Univ. of Tokyo Yasuko HISAMATSUMEG VRVS Meeting @PSI June 2004
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  • Set up alpha source LED Chamber Inside PMT Alpha source( 241 Am ) LED Liq. Xe Yasuko HISAMATSUMEG VRVS Meeting @PSI June 2004
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  • Condition & Procedure alpha source : ~200Hz, LEDpulse height:4000p.e. ~ 7200 p.e./event pulse shape: ~10nsec rate: 500Hz ~ 10KHz Trigger: alpha self trigger (veto by LED driver pulse) Procedure Pedestal Run & Gain calibration using LED Alpha Run @ LED OFF Alpha Run @ LED ON (LED : high rate background) -Change LED Pulse height, rate and PMT gain Yasuko HISAMATSUMEG VRVS Meeting @PSI June 2004
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  • ZA1984 Rate Dependence @Liq.Xe Gain 1*10 6 Background:2.16A 1.26*10 7 p.e./sec 6.91A 4.05*10 7 p.e./sec ZA1984 Time dependence? = 4.45 *10 4 sec Stable output up to 2.16A is confirmed. Slight deterioration(?) of output was observed under very severe background. Yasuko HISAMATSUMEG VRVS Meeting @PSI June 2004
  • Slide 15
  • ZA1984 Rate Dependence @Liq.Xe Current of Crowding LED [ A] alpha peak (@LED ON) / alpha peak (@LED OFF) This instability is caused not by photocathode but by the bleeder circuit; Shortage of bleeder current Improved design of the bleeder Circuit; adding Zener Diode Yasuko HISAMATSUMEG VRVS Meeting @PSI June 2004
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  • Final Design of Bleeder Circuit NEC RD68S NEC RD82S Provide Voltage regulation with Zener Diode Yasuko HISAMATSUMEG VRVS Meeting @PSI June 2004
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  • Zener Diode NEC RD Series Low noise zener recommended by HPK Plastic package Electrical Characteristic (T=25 o C) Data sheet: http://www.necel.com/nesdis/image/D11444EJ5V0DS00.pdf TypeZener Volt.[V] MinZener Volt.[V]MaxTemp. Coeff.[mV/ o C] RD68S64.0072.00~70 RD82S77.0087.00~83 So tiny.. Yasuko HISAMATSUMEG VRVS Meeting @PSI June 2004
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  • Electrical Characteristic @Low temp. Electrical Characteristics of NEC Zener Diode were measured at room temperature and in liq. N2 Set up: NEC RD68S, 82S. 2 samples for each were tested in liq. N2. Yasuko HISAMATSUMEG VRVS Meeting @PSI June 2004
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  • Electrical Characteristic @Low temp. Current [A] Zener voltage [V] Room Temp.Liq.N2 RD68S RD82S No damage to the package Can be used in liq.Xe Sharp voltage drop at zener volt. also at low temp. generate good reference volt. Zener Voltage decreased by ~13V Reasonable (Temp.Coeff.) Measured by Hiroaki NATORI Yasuko HISAMATSUMEG VRVS Meeting @PSI June 2004
  • Slide 20
  • Conclusion Stable output from R9288 ZA series under the background up to 4 A in PISA PMT test facility Stable output up to 2 A (1.3 *10 7 p.e./sec) was confirmed also in Tokyo PMT test facility Electrical characteristics of Zener diode at low temperature were measured. Confirmed that zener diode can be safely used at low temperature. Start drawing final design of PMT bleeder circuit at HPK Waiting for final PMT prototype from HPK! Yasuko HISAMATSUMEG VRVS Meeting @PSI June 2004
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  • PMT test under the magnetic field Gain, effective QE of 2 PMTs were measured under the magnetic field. Geometry definition
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  • Setting PMT test box with a PMT and a blue LED COBRA full excitation Isc : 360A, Inc : 320A gain:(1.320.03)x10 6 (750V) : TB0585 : (1.730.03)x10 6 (750V) : TB0473 PMT LED
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  • TB0585 Magnetic field around LXe position was reduced successfully by compensation coil, less than 40G. Inner FaceOuter Face Side FaceFront Face 90 (weak) 0(normal) mag. field
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  • TB0473 90 (weak) 0(normal) mag. field Inner Face Outer Face Side Face Front Face
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  • Gain&Eff.QE under mag. field of 62G Gain can be recovered with higher HV. Effective QE (measured with LED light) is not recovered even when HV changed. The magnetic field in the LXe region is well below 40G (20% loss of effective QE at max). Gain curveEffective QE No magnetic field 62G data
  • Slide 27
  • Summary PMT test under the COBRA mag. field Response of the two sample PMTs was tested under the COBRA magnetic field. The magnetic field at realistic position of LXe is successfully compensated, less than 40G at all positions, and decrease of PMT output is found to be less than 40%. Gain can be recovered with higher HV setting.
  • Slide 28
  • Cryostat/PMT holder design Cryostat construction PMT holder design Cryogenics system design
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  • Cryostat Design Summary: This document is the specification reference for the builder of the MEG cryostat and it is organized in three main sections: General: 1.1 Introduction. 1.2 Project description. 1.3 Scope of work. Technical Requirements: 2.1 General technical requirements. 2.4 Recommendations for storage. 2.7 Recommendations for cleaning. 2.8 Packing and transportation. 2.9 Mechanical and leakage tests 2.10 Inspection, test and quality control plan. Management Requirements 3.1 Fabrication and control plan. 3.2 List of certificates and documentation required. 3.3 Schedule for construction, test and shipment. 3.4 List of drawing Delivery in Summer 2005 after all tests in a manufacturer
  • Slide 30
  • PMT support structure Basic ideas PMTs are inserted in slabs (inner, side, outer) and plates (front) in a clean condition. The slabs and plates are assembled into a shape in the cryostat. Supporting frames for the slabs and plates will be fixed to the cryostat with screws. Some other equipments will be attached on the supporting frames. Patch panel Temperature sensor Level meter Inner Outer Side Front (up) Front (low) 768 PMTs If we get more, we can put more on the outer side.
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  • Structure of slab/plate SideOuter Front Inner Possible to divide into 6 slabs
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  • Assembling Several technical issues Easy maintenance Assembling w/o crane in clean environment Relative position Mating parts between the support and slab Through screw holes 123 45 Main support frames Support for the front
  • Slide 33
  • Patch Panel Feedthrough High density due to limited space on the chimneys. A bundle of cables will be connected to one feedthrough connector. Cabling (grouping of PMTs) are limited due to the slab


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