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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.