Lab tests of Thick GEMs Lab tests of Thick GEMs (THGEM)(THGEM)
S. Dalla Torre, Elena Rocco, L. Ropelewski, F. Tessarotto
May – August 2007
Outline:Outline:
Geometry of the THGEM tested; Sources & Setup; First discouraging results; Different geometry and
encouraging results; The rim effect; Conclusions.
GEM PrincipleGEM Principle
70 µm
55 µm
5 µm
50 µm
GEM hole cross section Avalanche simulation
ElectronsElectrons
IonsIons
60 %
40 %
Some THGEM picturesSome THGEM pictures
R3
P1
W2
P1:D=0.8 mmPitch=2 mmRim=0.04 mmThick=1mm
R3:D=0.2 mmPitch=0.5 mmRim=0.01 mmThick=0.2mm
W2:D=0.3 mmPitch=0.7 mmRim=0.1 mmThick=0.4mm
R3 section
Sources & Parameters of the Sources & Parameters of the THGEMs usedTHGEMs used
THGEMDiameter
(mm)Pitch(mm)
Rim(mm)
Thick(mm)
W1 0.3 0.8 0.1 0.4
W2 0.3 0.7 0.1 0.4
*P1 0.8 2 0.04 1
*P2 0.8 2 0 1
R3 0.2 0.5 0.01 0.2
R4 0.3 0.7 0 0.4
Sources Photons energy
Average number
of primary electron
s in Ar/CO2 (70/30)
Rates available
55Fe5.87 KeV 210
W/O collimatio
n up to 300 Hz
X-Ray (Cu) 8.8 KeV,
8.9 KeV 320
With collimation (1mm of diameter) up to 120
KHz
*Except for the Pi geometry we always used 30/70 CO2/Ar gas mixture !!
Structure of the chamber used Structure of the chamber used for testingfor testing
DRIFTDRIFT
THGEMTHGEM
GAS INLETGAS INLET
Section view of the structure Section view of the structure inside the chamberinside the chamber
Non segmented anode (copper foil);
Inlet and outlet (on the cover) for the gas;
Flux gas of 5 l/h.
IMPORTANT: Before installing bath, backing in the oven of the THGEM to avoid leakage current.
THGEM
d_ind
d_drift
DRIFT
ANODE
Cu X-Ray setupCu X-Ray setup
Electronics Setup and Electronics Setup and acquisitionacquisition
THGEM in the chamber
Power Supply
CAEN 471A
Gas system with mass flow meter mixing (30%CO2 70% Ar)
142 A ORTEC
Preamplifier
G 472 ORTEC
Amplifier
Digital Oscilloscope
ADC (LRS 2259 12 ch)
+ DAQ (CAEN controller
C111)
FAN I/O Le Croy 428F
DISCRIMINATOR Le Croy 821
SCALER CAEN N 145
Delay
0 20 40 60 80 100 120200
300
400
500
600
700
800
900
1000
1100
Iron Source collimated (dcollimator
=2 mm);Rate = ~40 Hz;E
induction= 2 KV/ cm;
Edrift
= 0.25 KV/ cm;DeltaV
GEM=1.8 KV.
Peak
Pos
ition
(AD
C c
hann
els)
Time (hours)
THGEM: d= 0.3 mm, pitch=0.7 mm, thick=0.4 mm, rim=0.1 mm.
0 200 400 600 800 1000 1200-5
0
5
10
15
20
25
30
35
40 Data: RUN0105_BModel: Gauss Chi^2/DoF = 9.18579R^2 = 0.86598 y0 1.24108 ±0.13856xc 444.52215 ±1.5512w 233.77693 ±3.71129A 6574.53452 ±114.51556
Cou
nts
ADC channels
Spectrum Guassian Fit
@ out of the ADC range
Gain
vari
ati
on
s la
rger
than a
fact
or
of
2 !
W2
d=0.3mm
Pitch=0.7mm
Rim=0.1mm
One of the first trial: scan in time @ 40 Hz One of the first trial: scan in time @ 40 Hz with the THGEM characterized by the with the THGEM characterized by the
“Weizmann geometry”“Weizmann geometry”
Our best result so far with Our best result so far with RR33
((d=0.2mm pitch=0.5mm d=0.2mm pitch=0.5mm
rim=0.01 thick=0.2mmrim=0.01 thick=0.2mm))
0 20 40 60 80 100150
200
250
300
350
400
450
500
550
Delta_VTHGEM
=1.05 KVE
induction= 3 KV/ cm
Edrift
= 2.1 KV/ cm
Uncollimated 55Fe source
Peak
Pos
itio
n (A
DC
cha
nnel
s)
Time (hours)
15%
55Fe Source Uncollimated Rate =260 Hz
Long time scan (~ 4 days)
0 2 4 6 8 10 12 14 16 18150
160
170
180
190
200
210
220
230 Delta_VTHGEM
= 1.05 KVE
induction= 3 KV/ cm
Edrift
= 2.1 KV/ cmCollimated X-Ray source
Peak
pos
ition
(AD
C c
hann
els)
Time (hours)
<10%
X-Ray Source Collimated Rate =6.6 KHz
Short time scan (< 1 days)
R3
0 200 400 600 800 1000 12000
20
40
60
80
100
120
140
Einduction
= 3 KV/ cmDelta_V
THGEM= 1.05 KV
Edrift
= 2.1 KV/ cm
Cou
nts
ADC channels
Gaussian fit - 55Fe source - Peak @ 447.8 ADC channels Gaussian fit - X-Ray source - Peak @ 593.5 ADC channels
RATE=460 Hz
R=
primary e- in 55Feprimary e- in X-Ray
R=
210320
= 0.66
R=
ADC ch. peak position with 55FeADC ch. peak position with X-Ray
R=
0.74563.5
=417.8
Comparison between different Comparison between different sourcessources R3
Rate capabilityRate capability
0 20 40 60 80 100 120
180
190
200
210
220
230
240
250
260
270
280
290
E_induction=3KV/ cmE_drift=2.1KV/ cmDelta V_GEM =1.05 KVX-Ray source - collimated d=1mm
Peak Measured current over rate
Rate (KHz)
Peak
Pos
ition
(AD
C c
hann
els)
4.00E-014
4.50E-014
5.00E-014
5.50E-014
6.00E-014
Current over R
ate
R3
Rate effect on signal amplitude: ~ 20%, varying the rate by 3 orders of magnitude! Also, from current measurement gain ~ 700
0 200 400
0
200
400
600
800
1000
1200
Same conditions about the E_ind and the E_driftIron source uncollimated
Cou
nts
ADC channels
Delta V 1.05 KV --> 260Hz Delta V 1.025 KV --> 260 Hz Delta V 1 KV -->235 Hz Delta V 0.975 KV --> 100 Hz
Cut spectrum due to the threshold on the discriminator giving the trigger signal
970 980 990 1000 1010 1020 1030 1040 1050
5.4
5.6
5.8
6.0
6.2
6.4
6.6
6.8
7.0
Gai
n Est
imat
ion
(log
sca
le)
Delta V_GEM
Gain Estimation Linear fit
‘
Gain const e –V/t
t ~ 50V
R3
Gain Estimation for different Gain Estimation for different signal amplitudessignal amplitudes
Rim effectRim effectIs this dramatic gain increase with time a rim
effect?
(Recall that the increase is much smaller with 10 micron rim).
Try thicker THGEM, larger holes w/o rim …
We come back to the Weizmann We come back to the Weizmann geometry (d=0.3 mm, pith=0.7 mm, geometry (d=0.3 mm, pith=0.7 mm,
thick=0.4), but w/o rimthick=0.4), but w/o rim
NONO gain increase with gain increase with time !time !
0 4 8 12 16 20 24100
120
140
160
180
200
Not collimated Iron source.Rate = 200 Hz.Thr in the discriminator 150 mV.E
induction =3 KV/ cm.
Edrift
= 1.42 Kv/ cm.Delta V
GEM =1.38 KV.
Electronics gain = 50
The 0 hour doesn't correspond to the starting 0-point irradiation of the chamber.
Cou
nts
Time (hours)
THGEM w/ o rim: d=0.3 mm; pitch=0.7 mm; thick=0.4mm.
but again stability only at moderate gains (~ 700) next step: chemical polishing to remove sharp edges and asperities due to copper drilling.
Time stability- THGEM Time stability- THGEM polished chemicallypolished chemically
0 2 4 6 8
240
260
280
300
320
340
360
380THGEM: d=0.3 mm, pitch=0.7 mm, thick=0.4 mm, rim=0;Delta_V
GEM=1.45 KV
Einduction
=3 KV/ cmE
drift=1.54 KV/ cm
X-Ray source collmated (1mm of diameter)Rate=6.7 KHzGas mixture 30/ 70 CO
2/ Ar
Peak
Pos
ition
(AD
C c
hann
els)
Time (hours)
Short time scan
0 200 400 600
0
20
40
60
80
100
120
Data: RUN0376_BModel: Gauss Chi^2/DoF = 9.90081R^2 = 0.97639 y0 0 ±0xc1 290.3548 ±0.46501w1 46.43951 ±1.26211A1 2673.40679 ±129.68217xc2 248.37102 ±1.25079w2 116.73933 ±1.28633A2 7248.22378 ±146.5686
Cou
nts
ADC channels
ADC spectrum
Before chemical polishing
After chemical polishing
Residuals after mechanical drilling
THEN WE CREATE A SMALL RIM!!!
Rate capability – THGEM Rate capability – THGEM polished chemicallypolished chemically
0 20 40 60 80 100 120
300
320
340
360
380
400 Peak Position Current over Rate
Rate (KHz)
Peak
Pos
ition
(AD
C c
hann
els)
3.20E-014
3.40E-014
3.60E-014
3.80E-014
4.00E-014
4.20E-014
4.40E-014
4.60E-014
4.80E-014
E_induction=3KV/ cmE_drift=1.54KV/ cmDelta V_GEM =1.45 KVX-Ray source - collimated d=1mm
Cu
rren
t ove
r rate
Conclusions:Conclusions: In the very near future we are :
Characterizing a DOUBLE THGEM configuration;
Measuring the first THGEM coated with the CsI in the test beam;
The work is in progress (and promising!), but there’s still a long way to go: Geometry role; Technological production; Different gasses….