Xenon Detector StatusXenon Detector Status

Liquid Xenon Group

2

OutlineOutline

• Detector Setup

• Operation

• Performance

• Problems and solutions

Detector SetupDetector Setup

4

PMT installation completedPMT 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

Sensors, LEDs, and alpha sourcesSensors, 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

Cabling and Al filler installationCabling 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…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 were 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

Xe leak

Warm vessel vacuum

~1 bar xenon

vacuum

Mass spectrometer

8

RGA of leaking xenonRGA 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 coversClosing the covers

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

10

Pressure/leak testPressure/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 rateEstimation of xenon leak rate

y = 10.9x - 0.3403R2 = 0.9825

y = 0.1187x - 0.0083R2 = 0.9617

0.001

0.01

0.1

1

10

0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16Xenon Gas Pressure [MPa]

Peak

Ion

curr

ent a

t A=6

6 [x

10̂-1

0 A]

Recycled gasket10-4 mbarl/sec leakRoom temperature xenon gas

New gasket

Room temperature xenon gas

Better at low temperature

OperationOperation

13

Gas/liquid systemGas/liquid system

Gas-phase purifier

Liquid-phase purifier

Detector1000L dewar

High pressureStorage

Gas line

Liquid line

14

Evacuation and liquefactionEvacuation 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

Liquid transferLiquid 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

End of xenon fillingEnd of xenon filling

temperature

Level meter

• Additional 10 liter was transferred for assurance

17

How many liters of liquid xenon?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

Slow ControlSlow Control

Detector, storage, dewar, purifiers

MEG Central DAQ System

(SCFE)

For shift crew use

Labview

megon00 PC in barrack

XEC PC 2

For expert use

Labview

XEC PC 1

XEC dedicated SCFENode cooperationAlarm to experts

Important controls are implemented in SCS nodes

19

Liquid circulationLiquid 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. InverterOMRON

PT

20

Succeeded!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

Liquid-phase purificationLiquid-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

Absorption LengthAbsorption Length

• Ratio Ratio Data/MC Data/MC vs vs distance fitted with an distance fitted with an exponential curveexponential curve..

• Inner and Outer face Inner and Outer face PMTsPMTs

• Cosine of incidence Cosine of incidence angle angle < -0.2< -0.2

• Slope compatible with Slope compatible with zerozero (no absorption)(no absorption).. > 3 m @95 % C.L.> 3 m @95 % C.L.

n̂

PMTPMT

Alpha source

After 50 h purification, 4/Nov

PerformancePerformance

2D display, charge/time 2D hist, charge:PMT# 3D reconstructed position

Waveform 1D histograms Charge:event#

24

PMT CalibrationPMT Calibration

• PMT calibration– LED

• PMT gain– Flushing LEDs at different

intensities

– Npe~1/2

• Time offset calibration– Viewing one LED flushing

with many PMTs simultaneously

– Alpha• QE and absorption length e

valuation• Liquid and cold gas

25

Time offset determinationTime offset determination

• Possible method only in non-segmented detector like ours• c’ is obtained by using all data

Tj

li,j-li-1,j

1/c’ti –ti-1

jji

ij Dc

ltT

',

MeasuredFlashing

Time

Of

i-th

LED

Speed of LED light

Offset of j-th PMT

Different LEDs viewed by one PMT

RD run

(ultra low)

txe - tTC

26

C-W runC-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 run - Pi0 calibrationCEX run - Pi0 calibration

• CEX process– -p0n

• 0(28MeV/c) • 54.9 MeV < E() < 82.9 MeV

• LH2 target

0

54.9MeV 82.9MeV

1.3MeV for >170o

0.3MeV for >175o

170o

175o

• NaI tagging counter– 3x3 crystals, APD readout

• Pb collimator panel in front of the Xe detector

28

LHLH22 Target 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 DetectorNaI Detectorbe

am a

xis

+/- 2

1 (+

/- 0.

07)

deg.

Up/down+/- 60 (+/- 0.005) deg.

30

CEX run data analysis, preliminaryCEX 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

Time MeasurementTime 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 tXe – tsci

280ps

115ps

Intrinsic resolution by T-B analsysis

32

Position MeasurementPosition Measurement

• Using collimator run data,

33

Physics runPhysics 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

Problems found in 2007Problems found in 2007andand

solutions for 2008 runsolutions for 2008 run

35

FeedthruFeedthru• 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?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

InstallationInstallation• 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/hour– Completed early morning of 24/Oct

• 2 weeks interruption of DAQ

38

PMT status after replacing feedthruPMT status after replacing feedthru

• Stable operation after replacing feedthru

• LED intensity optimization– Better gain evaluation than

before

39

As a bonus…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)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

Heat loadHeat 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?

PMTCableChimneyRadiationSupportCu pipe?

?

Pipes

PMTs

Cables

42

LN2 cooling pipeLN2 cooling pipe

• Cu pipe feedthru SUS pipe feedthru

43

Cooling PowerCooling Power

PC150 Cooling power at PSI - 24 Aug.,2007

0

40

80

120

160

200

240

60 80 100 120 140 160 180

Temperature (K)

Hea

ter P

ower

(W)

LYBOLDT6000 6.5kW at 50HzOrifice: 3577.5K 0W 123K 100W143K 150W 155K 180WVac: ~10-2 Pa

165K

0704KEKCW701

0708PSI

44

Blow up of low temperature valveBlow 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 nutPlug or shaft

Wilson Seal

Wilson SealAir

xenon

bellows

Liquid xenon

45

PMT Signal SplitterPMT 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

PMTsplitter

46

Light YieldLight YieldDiscrepancy between Discrepancy between and and data 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 goodImprovement and plateau of light yield of both gammas and alphas

• Have a look on WF

47

triplet= 22 ns

recomb= 45 ns

WaveformsWaveforms

= 21 ns

= 34 ns

! Careful treatment of electronics time constant is necessary

Xe

Xe X

e

Xe

Xe

Xe X

e

Xe

ee

ee

ee

A

Q

Q/A

Before purification 02.025.1/

/

AQ

AQ

was 1.93+/-0.02 in LP test

Electronegative impurity?

Oxygen??

48

Electronegative Impurity RemovalElectronegative 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

49

Current Status and ScheduleCurrent 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