Recent thgem investigations
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Recent THGEM investigations. Gain: UV vs. X-rays - Gain stability What’s next?. A. Breskin, V. Peskov, J. Miyamoto, M. Cortesi, S. Cohen, R. Chechik Weizmann Institute. THGEM cooperation also with: Coimbra, PTB, Soreq NRC, Milano univ, UTA…. THGEM Recent review w refs: BRESKIN et al

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Recent THGEM investigations

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Recent thgem investigations

Recent THGEM investigations

  • Gain: UV vs. X-rays- Gain stability

  • What’s next?

A. Breskin, V. Peskov, J. Miyamoto, M. Cortesi, S. Cohen, R. Chechik

Weizmann Institute

THGEM cooperation also with: Coimbra, PTB, Soreq NRC, Milano univ, UTA…

THGEM Recent review w refs: BRESKIN et al

http://dx.doi.org/10.1016/j.nima.2008.08.062

RD51 Paris Oct 08


Among current applications

photons

Gy/h

mm

mm

Among current applications:

2-phase LXe detectors

for rare events

Medical: LXe Gamma camera

Also: Calorimetry

LXe

Gas photomultipliers

N-detectors

n elemental radiography

Pos-sens n-dosimetry - BNCT


Thgem

THGEM

ThickGas Electron Multiplier (THGEM)

THGEM

1e- in

0.5mm holes

holes drilled

in thick G-10

E

104-105e-s out

  • SIMPLE, ROBUST, LARGE-AREA

  • Intensive R&D

  • Many applications

Double-THGEM: 10-100 higher gains

Robust

Single-photon sensitivity

Effective single-photon detection

8ns RMS time resolution

Sub-mm position resolution

>MHz/mm2 rate capability

Cryogenic operation: OK


Gain uv vs x rays

Gain: UV vs X-rays

To clarify:

“are WIS previous results of “higher gain with UV compared

to x-rays” - OK?

Method: compare both UV and x-rays with the

same detector in a single experiment


Recent thgem investigations

Single- & double-THGEM with UV (recall)

Shalem et al NIM A558(2006)475

0.8mm thick

0.4mm thick

104

104

104

  • Gain 2-THGEM / 1-THGEM ~100

  • Gain 2-THGEM: function of Etrans

  • 2-THGEM: lower Vhole

  • 1-THGEM: low thickness-effect on gain:

  • gain0.8mm/gain0.4mm~2


Recent thgem investigations

Double-THGEM with 6 keV x-rays (recall)

104

Cortesi et al 2007 JINST 2 P09002


Recent thgem investigations

New measurements: Experimental set up

pA

Gas in

pA

TGEM

-Vtop

CsI

To pump

Am

(for gain calibration)

Gas out

2cm

Mesh

-Vdr

Window

THGEM geometry:

Holes dia: 0.5 mm Pitch: 1 mm

Thickness: 0.8 mm

Rim: 0.1mm

UV light

55Fe

Hg lamp


Recent thgem investigations

Single-THGEM : Ar+5%CH4

UV

Current-mode

NEW

WIS old

pulse-mode

55Fe NEW

Pulse-mode

(~1kHz)

Cu X-ray gun, current-mode

Maximal gains with UV are 100 times higher than with X-rays.

For UV and x-ray gun:

The current in the plateau region (500-750V) was the same: 0.1nA.

The maximum current in gain measurements was always kept below 0.5nA

104

THGEM geometry:

Holes dia: 0.5 mm Pitch: 1 mm

Thickness: 0.8 mm

Rim: 0.1mm


Recent thgem investigations

Single-THGEM: Ne

104

UV,

current-mode

104

55Fe

Pulse-mode

THGEM geometry:

Holes dia: 0.5 mm Pitch: 1 mm

Thickness: 0.8 mm

Rim: 0.1mm

The maximum gains with x-rays in Ne are higher than in Ar+5%CH4.

In Ne breakdown voltages with UV and X-rays are closer.


Single thgem ne ch 4

104

104

UV

Current-mode

55Fe

Pulse-mode

Single-THGEM: Ne + CH4

THGEM geometry:

Holes dia: 0.5 mm Pitch: 1 mm

Thickness: 0.8 mm

Rim: 0.1mm

UV

Current-mode

104

55Fe

Pulse-mode

104

Same as with Ne: maximum gains with x-rays in Ne+CH4 are higher

than in Ar+5%CH4 and breakdown voltages with UV and X-rays are close.


A possible interpretation peskov

  • Raether limit: established in large-gap avalanche detectors but valid for MPGDs (Ivanchenkov NIM A 1999), though may be different

  • A*n0=106-107 electrons

  • where A is the maximum achievable gain, n0-number of primary electrons deposited by the

  • radiation in the drift region

  •  X-rays: different gain compared to UV

  • - In Ne/CH4 Raether limit possibly differs from Ar/CH4due to ~ 5-fold longer range of 55Fe photoelectrons (~1mm), resulting in lower ioinization density per “hole”.

A possible interpretation (Peskov)

To verify with alphas, hadronic beams etc


Gain stability

GAIN STABILITY


Recent thgem investigations

THGEM Long-term stability: recall

ST PC

1mm

i

Gain

R. Chechik SNIC2006, http://www.slac.stanford.edu/econf/C0604032/papers/0025.PDF

104

  • Insulator Charging up 

  • Hole&rim:few hours of stabilization

  • (gain variation ~ factor 2.)

  • Stabilization time function of:

  • Total gain (potentials)

  • Counting rate (current)

  • Material & hole-geometry (dia.,rim)

  • Production method

  • Gas & purity (e.g. moisture)

Ar/5%CH4

UV, 5x105 e-/mm2


Stability with uv new data

Stability with UV: new data

Single-THGEM geometry:

Holes dia: 0.5 mm Pitch: 1 mm

Thickness: 0.8 mm

Rim: 0.1mm

Ar/5%CH4 – flow mode

Charge-up: gain dependent


Recent thgem investigations

2nd THGEM

1st THGEM

Anode Mesh

Drift mesh

9.6 mm

1.6 mm

1.6 mm

THGEM GAIN STABILITY – X-RAYS

Vary the distance

To change the rate

Fe-55 source collimated

by a 3 mm dia hole

THGEM geometry

Material FR-4

Thickness 0.4 mm

Hole size 0.6 mm

Pitch 1.0 mm

Rim size 0.1 mm

E_drift = 100 V/cm

E_transfer 1 kV/cm

E_inducion= 4 kV/cm


Recent thgem investigations

SETUP

Heated Baraton Gauge

for pressure monitoring

(4Torr change in 24h)

Pure argon gas in

UHV vessel

ThGEM

Temperature sensor placed on

the chamber surface (0.8C in 48h)

Hamamatsu PMT for photon

counting

Collimated X-rays

Anode

signal

Gas can:

- Flow

- Circulate via getter

Gas out

RGA 200 gas analyzer

for purity check

Charge Amp+Shaper+MCA

for pulse height analysis

Gain corrected for pressure-changes; T-changes negligible


Recent thgem investigations

GAIN VARIATION vs RATE I

  • For a very short-term scales (<1 hr), the drop in gain is faster for higher rates

  • The magnitude of drop function of rate

7Hz/mm2

Gain 2000

30Hz/mm2

120Hz/mm2

300Hz/mm2

X-RAYS

Argon, 770 Torr


Recent thgem investigations

GAIN VARIATION vs RATE II

Stability reached after ~ 5h for gains ~1400 for 7-300Hz/mm2

7Hz/mm2

Gain 2000

Data normalized to pressure=770 Torr

300Hz/mm2

X-RAYS

Argon, 770 Torr


Recent thgem investigations

GAIN VARIATION vs RATE – higher gain vs rate

  • At higher rate, after initial drop, the gain keeps rising while at lower rate the gain stabilizes at low value.

  • 2. At higher rate the detector occasionally discharges, whereas at lower rate the detector is rather stable

  • 3. Gain recovery after a discharge is faster at higher rates.

Gain 10,000

At high rate

continuous sparks

begin when

the gain recovered

sufficiently

Spark followed by slow

recovery (low rate)

Sparks followed by quick recovery (high rate)


Recent thgem investigations

GAIN VARIATION vs RATE – lower gain vs rate

Lower gain: rates 7 Hz/mm2 & 70 Hz/mm2

1. At higher rate, the initial drop is shaper

2. At higher rate, after the sharp drop the gain tends to reach faster

the stability observed for the lower rate.

3. The stabilization time is longer for low gain & higher rates.

Gain 500


Recent thgem investigations

Summary of charge up in pure Ar

  • At low rates: gain drops to a certain level and remains constant regardless of initial gain (500-10,000)

  • 2. At higher rates: gain sharply drops to its minimum. The magnitude of the drop is the largest at high gain. After reaching minimum, the gain tends to recover to the value reached at low-rates. The recovery is faster at the higher gains.

  • 3. At high rate and high gain the gain recovery did not reach stable level – discharges due probably Raether limit in Ar.


Recent thgem investigations

GAIN STABILITY: rim/no-rim TRIESTE RESULTS

Long time GAIN variation

RIM: 0.1 mm

Single THGEM, th. 0.4, Ø 0.4, p. 0.8

RIM: 0

Short time GAIN variation

TRIESTE Results

RIM: 0

RIM: 0.1 mm

irradiation after ~10 hour at nominal voltage without irradiation

irradiation at HV switch on (after ~1 day with no voltage)

Remark: Comparison at diff gains

Fulvio TESSAROTTO


Gain variation studies in different conditions trieste results

Gain variation studies in different conditionsTRIESTE results

For first series of “Eltos” pieces (with th. 0.4, diam. 0.4, pitch 0.8),

Ar/CO2 70/30 and 55Fe source (~ 600 Hz), in Trieste, first 12 h:

100 μm chem. rim  increase of ~ 400%

50 μm mech. rim  still to be processed: large decrease

25 μm chem. rim  decrease of ~ 70%

10 μm chem. rim  decrease of ~ 50% (“global etching”)

no rim  decrease of < 30%

The time to reach stabilization is shorter for smaller rims

CsI deposited on pieces with 100 μm rim and with no rim:

gain variations with photons ~ similar to those seen with X rays

?

Fulvio TESSAROTTO


Recent thgem investigations

THGEM-GPM for LXe Gamma Camera

Subatech-Nantes/Weizmann

THGEM

CsI

photocathode

LXe conversion volume

Segmented

Anode

IN CONSTRUCTION

LXe/GPM Tests: Jan 09

MgF2 window


300x300mm2 thgem

300x300mm2 THGEM!


300x300 thgem

300x300 THGEM

THGEM geometry:

Hole dia.: 0.5 mm

Pitch: 1 mm

Thickness: 0.4 mm (Cu~ 35 mic)

Rim: 0.05 mm (can be smaller)

Chemical etching/no mask

Ni/Au plating

Producer:

Print Electronics

www.print-e.co.il


Summary

SUMMARY

● In Ar+5%CH4 the maximum achievable gains measured with UV-light (~106)

are ~100-fold higher than with 55Fe (~104)

● Probable explanation is the Raether limit

● In Ne and Ne-CH4 (5-23%) mixtures, under gas flushing, the maximum gains

with UV and 55Fe are closer (105 - 106)

● Possibleexplanation: 55Fe photoelectron-tracks are longer in Ne and its

mixtures lower density of ionization per hole  lower max. gain-difference

caused by charge-density effects.

● In pure Ne scintillation prevents high gains & “masks” p.e. extraction quencher

● For RICH: optimal would be Ne–based mixtures

● Quencher additives to be optimized – for high gain and efficient p.e. extraction.

● Preliminary results indicate upon ~70% extraction efficiency in Ne/23%CH4

similar to Ar/5%CH4.

●Charge-up: geometry (rim), gain and rate dependent.

● It seems that rimless holes are advantageous, but need to establish detectors’

parameters (eff QE, e-transfer photon detection efficiency) with the right conditions

and gas

● Need to compare stability of LARGE-AREA rim/rimless THGEMs with UV photons

● Tests in RICH mode? Who? When? – Trieste ordered 60x60 cm THGEMs.

● 30x30cm THGEM tests: tested end 2008 at WIS

● Expected results in Cryo-THGEMs Gas Photomultipliers/LXe: early 2009.


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