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Xenon Detector Status

Liquid Xenon Detector Group

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

PMT R&D

Photocathode New breeder circuit with zener diodes Test under the COBRA magnetic field

MotivationUnder 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 R6041QNot 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 testedunder high rate background environment.

K-Sc-Sb + Al strip used in R9288Al 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 PatternLow surface resistance

R9288 ZA series

Yasuko HISAMATSU MEG VRVS Meeting @PSI June 2004

R6041Q (Rb-Sc-Sb w/o Al strip used in LP)

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200 250

ratioratio(LED)

Serial #

Beam on

83MeV

55MeV

Lab test

Test LED with crowing LED (0.8 microA)

-105oC 25oC

Only base currentshortage effect

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 CurrentAns. 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 HISAMATSU MEG VRVS Meeting @PSI June 2004

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.

PMT fast change mode successfully tested Linear motion to “dip” PMTs Gate valve to isolate N2/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

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 -109°C (1 Atm)

Note: usually Xe kept at -105, 1.3 Atm

ZA1985

ZA1980

Crowding ON OFF

I=4 A

TB604

ZA1985

ZA1980

Pla

teau

/Pea

k

New 9288 (ZA1980 and ZA1985) compared to TB604 (in Ar gas and LXe)

PMT Rate Dependence Test in Tokyo

Xe tankLiq.Xe chamber

Purification system

PMT Test facility @Univ. of Tokyo


Set up

alpha source

LED

Chamber Inside

PMT

Alpha source(241Am )

LED

Liq. Xe


Condition & Procedure

alpha source : ~200Hz, LED pulse height:4000p.e. ~ 7200 p.e./event

pulse shape: ~10nsecrate: 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


ZA1984 Rate Dependence @Liq.Xe Gain 1*106

Background: 2.16µA1.26*107p.e./sec

6.91µA4.05*107p.e./sec

ZA1984Time dependence? = 4.45 *104sec

Stable output up to 2.16µA is confirmed. Slight deterioration(?) of output was observed under very severe background.


ZA1984 Rate Dependence @Liq.Xe

Current of Crowding LED [ µA]

alpha peak (@LED ON) / alpha peak (@LED OFF)

This instability is caused not by photocathodebut by the bleeder circuit;Shortage of bleeder current

Improved design of the bleeder Circuit;adding Zener Diode


Final Design of Bleeder Circuit

NEC RD68S

NEC RD82S

Provide Voltage regulation with Zener Diode


Zener Diode NEC RD Series Low noise zener recommended by HPK Plastic package Electrical Characteristic (T=25oC)

Data sheet:http://www.necel.com/nesdis/image/D11444EJ5V0DS00.pdf

Type Zener Volt.[V] Min Zener Volt.[V]Max Temp. Coeff.[mV/oC]

RD68S 64.00 72.00 ~70

RD82S 77.00 87.00 ~83

So tiny..


Electrical Characteristic @Low temp.

Electrical Characteristics of NEC Zener Diode were measured at room temperature and in liq. N2Set up:

NEC RD68S, 82S.2 samples for each were testedin liq. N2.


Electrical Characteristic @Low temp.

Current [µA]

Zener voltage [V]

Room Temp. Liq.N2

RD68S

RD82S

No damage to the package Can be used in liq.XeSharp 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


Conclusion Stable output from R9288 ZA series under the

background up to 4A in PISA PMT test facility Stable output up to 2A (1.3 *107p.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!


PMT test under the magnetic field Gain, effective QE of 2 PMTs were

measured under the magnetic field.

Geometry definition

Setting

PMT test box with a PMT and a blue LEDCOBRA full excitation Isc : 360A, Inc : 320A

gain:(1.32±0.03)x106 (750V) : TB0585 : (1.73±0.03)x106 (750V) : TB0473

PMT

LED

TB0585

Magnetic field around LXe position was reduced successfully by compensation coil, less than 40G.

Inner Face Outer Face

Side Face Front Face

○ 90°(weak)× 0°(normal)▲ mag. field

TB0473○ 90°(weak)× 0°(normal)▲ mag. field

Inner Face Outer Face

Side Face Front Face

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 curve Effective QE

No magnetic field62G data

SummaryPMT test under the COBRA mag.

fieldResponse 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.

Cryostat/PMT holder design

Cryostat construction PMT holder design Cryogenics system design

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 Requirements3.1 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

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 PMTsIf we get more, we can put moreon the outer side.

Structure of slab/plateSide Outer

Front

InnerPossible to divide into 6 slabs

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

1 2 3

4 5

Main support frames

Support for the front

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 structure.

Grouping of PMTs can be arranged between the patch panel and feedthrough connector.

Cold Vessel

Patch Panel

feedthrough

Warm Vessel

Cryogenic System Design

Xenon strage/1000 L Dewar/Purifier Storage tanks ready at PSI 1000 L dewar design completed Purifier on the way to PSI

(16/June)

PMT Calibrations

Alpha-on-a-wireSimulation of a wire in the Large PrototypeSimulation of the final calorimeter

Neutron generators (AB’s talk in last meeting)Selective activation (Ni)Acquiring information on availability/price

Photons-from-the-back(AB’s talk in last meeting)Feasibility study in progress

z

x

Large prototype: how many sources? 3 sources placed along x (0,±10cm) 1 Wire 50 m thick Search for a no time consuming source ID

Front face average (usual fast method) 2 opposite faces weighted average (the shadow effect

is compensated) Wire shadow: 1.5 MeV “lost”

5 sources in LP 5 sources make a more symmetrical situation (same

spacing as PMTs) Identification still possible at more than 3 but worse

than 3 sources

No effect on energy resolution

We checked the effect of the wire presence on energy resolution at 52.8 MeV

Linear fit training with no wire

Xe layer in front of the front face PMTs as in the last test

C-shape calorimeter

3 wires with 5 sources each (15 sources total) 50 m wires 2 mm wide alpha deposit on the wires (0, 7.5, 15 cm) from lateral face to lateral face Half radial depth = (0, 35)

>15 p.e. for d(pmt)<35 cm (5% QE) Easy to identify the wire, a bit more difficult to identify

the source (even in MC!!) Fast ID: front face averages Exploitation of the linear fit is in progress

Front face averages

Alpha/gamma ID

No problem with full reconstruction (MC!!)

LP: three or five sources easily distinguishible

Final calorimeter: some more work is needed to distinguish all 15 sources.

photons

Full reconstruction alpha

Front face fit

Another CEX beam test at E5

DAQ using almost final electronics/software Wave-form digitizer Software framework

Investigate Al-grid PMT performance Gain experience for using - beam at E5 (and

hydrogen target)

Schedule2002 2003 2004 2005

Test MilestoneAssemblyDesign Manufacturing

Large Prototype Beam Test Beam Test

Cryostat Vessel

PMT

Refrigerator

Liq. Purification

AssemblyTest

Engineering runs

Heater replaced

Neutron background measurement

Base circuit design must be finalized

Crane problem

NeutronShield?

Schedule in 2004

LPTNeutr.

BGPM + Src Inst

Pi- Beam

Test

Liq.

Purif.

Full Calorimete

r

Jun/2004 Jul/2004 Aug/2004 Sep/2004 Oct/2004 Nov/2004 Dec/2004

Neutron background measurement using LP in June, July Two Problems during start-up in June

Getter (xenon purifier) problem (triac error) control board must be changed refrigerator problem (He leakage) Replaced to the final refrigerator which will be ready soon.

PMT replacement and installation of a calibration wire (several active spots on a 100um wire.) is planned in Aug.

Another CEX beam test is planned in Sep/Oct Wave-form digitizer and new PMTs (at least on the front face)

Liquid phase purifier test on LP will be performed in Nov/Dec In 2005 LP chamber will be used for PMT test/calibration

Construction

Schedule in 2005

LPT

PMT testing + calibration

Full

Calorimeter

Cryo.

Installation

Crane+

Tent

AssemblyStudies

(Wed + remote)

Test

Jan-Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan

Jan-Mar/2005 Equipment installation (cryogenics, xe strage tank…) Aug-Sep/2005 PMT assembly in the cryostat Oct-Dec/2005 Operation test under the magnetic field will continue

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