Recent THGEM investigations

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

Weizmann Institute

RD51 Paris Oct 08

- Gain: UV vs. X-rays- Gain stability- What’s next?

THGEM Recent review w refs: BRESKIN et alhttp://dx.doi.org/10.1016/j.nima.2008.08.062

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

Among current applications:

Gy/h

mm mm

photons

LXe

Medical: LXe Gamma camera

Pos-sens n-dosimetry - BNCT

N-detectors

n elemental radiography

Gas photomultipliers

2-phase LXe detectors for rare events

Also: Calorimetry

THGEM

0.5mm holesholes drilledin thick G-10

Thick Gas Electron Multiplier (THGEM)

SIMPLE, ROBUST, LARGE-AREAIntensive R&DMany applications

1e- in

104- 105 e-s out

E

THGEM

Double-THGEM: 10-100 higher gains

RobustSingle-photon sensitivityEffective single-photon detection8ns RMS time resolutionSub-mm position resolution>MHz/mm2 rate capabilityCryogenic operation: OK

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

Single- & double-THGEM with UV (recall)Shalem et al NIM A558(2006)475

104

104

104

0.8mm thick

0.4mm thick

- 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

Cortesi et al 2007 JINST 2 P09002

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

104

pA

-Vdr

Hg lamp

TGEM

Window

-Vtop

55Fe

Am(for gain calibration)

pA

UV light

2cm

Mesh

New measurements: Experimental set up

To pump

Gas in

Gas out

CsI

THGEM geometry:Holes dia: 0.5 mm Pitch: 1 mmThickness: 0.8 mmRim: 0.1mm

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

Ar+5%CH4=1atm

1.00E-02

1.00E+00

1.00E+02

1.00E+04

1.00E+06

0 500 1000 1500 2000 2500

Voltage (V)

Gain UV light

X-rays 55Fe NEWPulse-mode(~1kHz)

Cu X-ray gun, current-mode

Single-THGEM : Ar+5%CH4

WIS old pulse-mode

UVCurrent-modeNEW

104

THGEM geometry:Holes dia: 0.5 mm Pitch: 1 mmThickness: 0.8 mmRim: 0.1mm

Gain in Ne=1atm

1.00E-03

1.00E-02

1.00E-01

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

50 150 250 350 450 550

Voltage (V)

Gai

n

UV lightFe old

(prtection box)

Fe new(no protection box)

Single-THGEM: Ne

UV, current-mode

55FePulse-mode

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.

104

THGEM geometry:Holes dia: 0.5 mm Pitch: 1 mmThickness: 0.8 mmRim: 0.1mm

104

Single-THGEM: Ne + CH4

Gains in Ne+5%CH4

1.00E-01

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

0 200 400 600 800 1000 1200

Voltage (V)

Gai

n

UVFe

Ne+23%CH4

1.00E-01

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

0 500 1000 1500 2000 2500

Voltage (V)

Gai

n

Fe

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.

55FePulse-mode

55FePulse-mode

UVCurrent-mode

UVCurrent-mode

THGEM geometry:Holes dia: 0.5 mm Pitch: 1 mmThickness: 0.8 mmRim: 0.1mm

104104

104 104

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/CH4 due to ~ 5-fold longer range of 55Fe photoelectrons (~1mm), resulting in lower ioinization density per “hole”.

To verify with alphas, hadronic beams etc

GAIN STABILITY

THGEM Long-term stability: recall

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)

i

ST PC 1mm

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

Gai

nAr/5%CH4

UV, 5x105 e-/mm2

104

Stability with UV: new data Single-THGEM geometry:Holes dia: 0.5 mm Pitch: 1 mmThickness: 0.8 mmRim: 0.1mm

Stabilty measured with UV in Ar+5%CH4=1 atm at gain=10

-0.50

0.51

1.5

0 50 100 150 200

Time (min)

Cu

rren

t (n

A)

Charge-up: gain dependent

Ar/5%CH4 – flow mode

THGEM GAIN STABILITY – X-RAYS

Fe-55 source collimatedby a 3 mm dia hole

Ano

de M

esh

2nd

TH

GE

M

1st T

HG

EM

Drif

t m

esh

9.6 mm 1.6 mm 1.6 mm

Vary the distanceTo change the rate

THGEM geometryMaterial FR-4Thickness 0.4 mmHole size 0.6 mmPitch 1.0 mmRim size 0.1 mm

E_drift = 100 V/cmE_transfer 1 kV/cmE_inducion= 4 kV/cm

SETUP

Collimated X-rays

Pure argon gas in

Gas out

ThGEM

Heated Baraton Gaugefor pressure monitoring (4Torr change in 24h)

Charge Amp+Shaper+MCAfor pulse height analysis

RGA 200 gas analyzerfor purity check

Temperature sensor placed on the chamber surface (0.8C in 48h)

Hamamatsu PMT for photoncounting

Anodesignal

UHV vessel

Gas can:- Flow- Circulate via getter

Gain corrected for pressure-changes; T-changes negligible

Charge up measurement for different rates (7, 30, 120, 300 Hz/mm2)

1 hour scale

1000

1200

1400

1600

1800

2000

2200

0 0.2 0.4 0.6 0.8 1

Tim e (hr)

Ga

in

Sept 21, Vent, Weak=7 Hz/mm2

Sept 22, Vent, Weak ~ 30 Hz/mm2

Sept 23, Vent, Slightly strong ~ 120 Hz/mm2

Sept 24, Vent, Strong ~ 300 Hz/mm2

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

Argon, 770 Torr

GAIN VARIATION vs RATE I

7Hz/mm2

30Hz/mm2

120Hz/mm2

300Hz/mm2

X-RAYS

Gain 2000

Charge up measurement for different rates (7, 30, 120, 300 Hz/mm2)

10 hour scale

1000

1200

1400

1600

1800

2000

2200

0 2 4 6 8 10

Tim e (hr)

Gai

n

Sept 21, Vent, Weak=7 Hz/mm2

Sept 22, Vent, Weak ~ 30 Hz/mm2

Sept 23, Vent, Slightly strong ~ 120 Hz/mm2

Sept 24, Vent, Strong ~ 300 Hz/mm2

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

Data normalized to pressure=770 Torr

GAIN VARIATION vs RATE II

X-RAYS Argon, 770 Torr

Gain 20007Hz/mm2

300Hz/mm2

High Gain ~10,000, High (170 Hz/mm2) and Low (7 Hz/mm2) Rates

0

2000

4000

6000

8000

10000

12000

0 2 4 6 8 10 12 14

Time (hr)

Gai

n

Oct 2, High Rate (~ 170 Hz/mm2), HV=1290V

Oct 3, Low rate (~ 7 Hz/mm2), HV=1260V

1. 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.

Sparks followed by quick recovery (high rate)Spark followed by slow recovery (low rate)

At high ratecontinuous sparksbegin whenthe gain recoveredsufficiently

Gain 10,000

GAIN VARIATION vs RATE – higher gain vs rate

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

1. At higher rate, the initial drop is shaper2. 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.

Low gain, High rate ~ 70 Hz/mm2, Low rate ~ 7 Hz/mm2

0

100

200

300

400

500

600

0 5 10 15 20

Time (hr)

Ga

in

Oct5 Low rate (~ 7 Hz/mm2), 770 Torr

Oct 5 High rate ( ~ 70 Hz/mm2), 770 TorrGain 500

GAIN VARIATION vs RATE – lower gain vs rate

Summary of charge up in pure Ar

1. 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.

Fulvio TESSAROTTO GDD meeting, CERN, 01/10/2008

Trieste THGEM news

RIM: 0.1 mm

RIM: 0

Long time GAIN variation

Short time GAIN variation

RIM: 0RIM: 0.1 mm

Single THGEM, th. 0.4, Ø 0.4, p. Single THGEM, th. 0.4, Ø 0.4, p. 0.80.8

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

irradiation after ~10 hour at nominal voltage without irradiation

TRIESTE Results

GAIN STABILITY: rim/no-rim TRIESTE RESULTS

Remark: Comparison at diff gains

Fulvio TESSAROTTO

GDD meeting, CERN, 01/10/2008

Trieste THGEM news

Gain variation studies in different conditions

TRIESTE 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

?

THGEM

Segmented

Anode

MgF2 window

LXe conversion volume

THGEM-GPM for LXe Gamma Camera

CsIphotocathode

Subatech-Nantes/Weizmann

IN CONSTRUCTIONLXe/GPM Tests: Jan 09

300x300mm2 THGEM!

300x300 THGEM

THGEM geometry:Hole dia.: 0.5 mm Pitch: 1 mmThickness: 0.4 mm (Cu~ 35 mic)Rim: 0.05 mm (can be smaller)Chemical etching/no maskNi/Au platingProducer:Print Electronics www.print-e.co.il

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)● Possible explanation: 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.