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….