Xenon Detector Status

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
• lt 200300um 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
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)

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
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
temperature
Level meter

• Additional 10 liter was transferred for assurance

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 2030 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
Slow Control
Labview
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
Liquid circulation
Purifier Cartridge Molecular sieves, 13X 25g water
Freq. Inverter OMRON

• Circulate xenon in liquid phase
• Circulation pump
• 100liter/h_at_3175rpm, Dp 0.2MPa
• Molecular sieves
• gt24 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
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 lt -0.2
• Slope compatible with zero (no absorption).

l gt 3 m _at_95 C.L.
After 50 h purification, 4/Nov
Alpha source
PMT
23
Performance
2D display, charge/time
2D hist, chargePMT
3D reconstructed position
Waveform
1D histograms
Chargeevent
24
PMT Calibration

• PMT calibration
• LED
• PMT gain
• Flushing LEDs at different intensities
• Npe1/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 Giovannis presentation

27
CEX run - Pi0 calibration

• CEX process
• p-p?p0n
• p0(28MeV/c) ? g g
• 54.9 MeV lt E(g) lt 82.9 MeV
• LH2 target

• NaI tagging counter
• 3x3 crystals, APD readout
• Pb collimator panel in front of the Xe detector

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 (lt 2cm)
• Select only center events ( u,v lt 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
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 threshold3.5V
• 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?
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)
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 1520 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
Heat load

• Pressure is slowly increasing under normal
  operating condition.
• Refrigerator cooling power 200W
• Expected redundant cooling power 100W
• Calculation based on LP modeling
• PMT37W (Vmean 775V)
• Conduction64W
• 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
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 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

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
Waveforms

• ?triplet 22 ns
• ?recomb 45 ns

ta 21 ns
tg 34 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/inst
  all/xenon.html