new thgem test in the compass hall

Fulvio TESSAROTTO GDD meeting, CERN, 01/10/2008 Trieste THGEM newsGDD meeting, CERN, 01/10/2008 Trieste THGEM news 11

New THGEM test in the COMPASSNew THGEM test in the COMPASS hallhall

Preparation of the test

Preliminary check with Fe source

The LED light sources

The test area in the COMPASS hall

Measurements with analog r/o

Measurements with digital r/o


Motivations for this testMotivations for this test

From:

- CsI photoelectron extraction and backscattering measurements

- first indications from simulation of fields and trajectories

- THGEM performances with different gases

we concluded that a methane based gas mixture is needed

We experienced difficulties in reaching high gains without sparks

Decision to build a quadruple THGEM Test it with light source Obtain authorization to use flammable gas Try to characterize the time response

The COMPASS RICH test area seemed to be the easiest choice


Preparation of the testPreparation of the test

Design and build a new chamber with:

- 9 HV connectors and 2 gas connectors,

- anode segmented in 16 pads,

- a fused silica window (Heraus Suprasil II)

- a flange for light source mounting

Design and build mechanics for:

- testing the LED light source behavior

- interfacing the light source to the chamber

Find low wavelength LED and best possible driver

Most important: involve many COMPASS colleagues for the test


Choice of THGEMChoice of THGEM

“Standard geometry”:

- Thickness = 0.4 mm

- Hole diameter = 0.4 mm

- Pitch = 0.8 mm

- Rim = 10 μm

Production:

- Laser + etching

- First set from ELTOS

Second best after “global etching”


The chamberThe chamber

anode

driftTHGEM 1

THGEM 2

Einduction

Etransfer2.0 mm

2.0 mm

2.0 mm

CsI

THGEM 3

THGEM 4

2.0 mm


55Fe source: rate ~ 200 Hz, primaries: ~ 200

Fields:Drift = Induction = 1.5 kV/cmTransf.1 = Trasnf.2 = 1.0 kV/cmTHGEM voltages:ΔV2 = ΔV3 = 1400 V

First test: triple THGEM, Ar-CH4 50-First test: triple THGEM, Ar-CH4 50-5050

ΔV1 (V)

largest gain with 55Fe source so far

THGEM: 30x30; 0.4, 0.4, 0.8, 10 μmSpacings: 2.0 mm (drift sp. = 4.0 mm)


55Fe source: rate ~ 200 Hz, primaries: ~ 200

Fields:Drift = Induction = 1.5 kV/cmTransf.1 = Trasnf.2 = 1.0 kV/cmTHGEM voltages:ΔV2 = ΔV3 = 1400 V

First test: triple THGEM, Ar-CH4 50-50First test: triple THGEM, Ar-CH4 50-50

THGEM: 30x30; 0.4, 0.4, 0.8, 10 μmSpacings: 2.0 mm (drift sp. = 4.0 mm)

Drift: + 160 pATop1: + 30 pABottom1: 0 pATop2: + 110 pABottom2: - 50 pATop3 : + 710 pABottom3: - 610 pAAnode: - 340 pA

Very interesting currents:Very interesting currents:


CsI deposited on one half onlyCsI deposited on one half only

CsI deposited by

Miranda Van Stenis

(A. Braem’s lab.)

on 17/02/2009

8 pads corresponding to the CsI coated half

8 pads corresponding to the uncoated half

CsI coated half uncoated half


We bought 2 LED’s of 255 nmWe bought 2 LED’s of 255 nmfrom “Laser 2000” company, Paris


First test of “255 nm LED”First test of “255 nm LED”

Check that the LED is properly working (no specifications available)

- power DC mode direct/inverse and check current

- try to see glow from UV light on fluorescent liquid

- characterize the LED emission spectra

- estimate and tune the LED light output in pulsed mode with PM

We then mounted it on the chamber with CsI coated THGEM:

- no measurable photocurrent seen

- with multiplication both signals and currents are seen

Conclusion: we can use it for the test

Colleagues from Freiburg bought a “270 nm LED”

able to provide pulses of 600 ns length, up to 40 MHz


Mechanics for the LEDMechanics for the LED

LED

quartz window

THGEM


Study of the LED with a Study of the LED with a MAPMTMAPMT

LED

quartz window

THGEM

MAPMT

50 μm pin-hole


Both seem to emit in a region where

CsI has extremely low Q.E., if any.

Using an Avantes

spectrophotometer

we measured the

emission spectra

for both “255 LED”

and “270 laser LED”

Emission spectra for LED “255” nm and Emission spectra for LED “255” nm and “270” nm“270” nm


Methane Detection Head

Methane Leaks Collector

Gas Distribution rack

Bottle of Ar/CH4 50/50

THGEM Detectors

Emergency Button

Power plugs

Electronics Racks

Sliding door

Bottle of Ar/CO2 70/30

Safety box for radioactive sources

COMPASS RICH THGEM TEST AREACOMPASS RICH THGEM TEST AREA

We have been authorized to use flammable gas: Ar-CH4 50-50 or pure CH4

for two weeks, after some interactions with the safety officers and filling of

a finite number of safety papers.


“255 nm” LED continuous current:

Voltages: 7150 7150 5525 5325 3775 3575 2150 1950 620

Amplitude spectra with “255 nm Amplitude spectra with “255 nm LED”LED”

For high rates the analog r/o piles up the signals;

lowering the rate we reach a minimum slope and

lowering it further the event rate changes without

changes in the slope of the spectra => single photon


Voltages: 7150 7150 5525 5325 3775 3575 2150 1950 620

Amplitude spectra from pulsed Amplitude spectra from pulsed LEDLED

Pulsed LED provides single photoelectrons with probability between 0.1% and 1%


Estimate of the gain: ~ 100,000Estimate of the gain: ~ 100,000

The chamber was very stable in these conditions


Random pulses – high frequency

Fixed frequency: 9kHzVoltages: 7100 7100 5500 5300 3750 3550 2150 1950 620

Amplitude spectra with “Freiburg Amplitude spectra with “Freiburg LED”LED”


Voltages: 7100 7100 5500 5300 3750 3550 2150 1950 620

Using FREIBURG pulsed LED:


Delta V1 increased by 30V


Saturation of AmplifierChanging the GAIN of the Amplifier

Zooming the low amplitude partZooming the low amplitude part

There is no clear evidence of “Polya” shape


First look at timing propertiesFirst look at timing properties

new thgem test in the compass hall

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