INFN Trieste, October 2008

Summary of measurements on:•CsI coated ThGEM

•triple ThGEM @ CERN

Single ThGEM M1 with CsI the currents at anode, bottom and top

are read out by the picoammeters

I top = I totale

1

10

100

1000

10000

0 200 400 600 800 1000 1200 1400

Delta V

cu

rre

nt

(pA

)

top 3000 V

top 2000 V

I anode/I totale

0%

10%

20%

30%

40%

50%

60%

70%

0 200 400 600 800 1000 1200 1400

Delta V

rati

o

ratio 3000 V

ratio 2000 V

two induction fields (4kV/cm, 6 kV/cm), V drift = 0

Scan in V: the light has been chosen to enhance the gain = 1 plateau

Different behavior of the charge sharing between anode and bottom at different gains:•HIGH gains, increasing the gain: more and more to the bottom•LOW gains, increasing the gain: more and more to the anode

1

10

100

0 500 1000 1500 2000 2500 3000 3500 4000

V top

I dri

ft (p

A)

Photocurrent, f(V drift) only the cathode is read-out

Single ThGEM C4 with CsIpreliminary measurements

Ar/CO2 1 atm

0.1

1

10

100

0 500 1000 1500 2000 2500 3000 3500

V top (V)

I cat

hode

(pA

)

0.1

1

10

100

1000

10000

0 500 1000 1500 2000

V

I an

od

e (

pA

)

Photocurrent at the cathodeV scan, no filtersonly the anode read-out

Single ThGEM C4 with CsIanode, bottom & top read-out

V induction = 2000V

1

10

100

1000

0 500 1000 1500 2000V (top - bottom)

I (p

A)

top

bottom

anode

Induction scan

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1000 1500 2000 2500 3000 3500

V induction

rati

o

Delta V = 1550 V

1480 V

1400 V

V induction = 3000 V

1

10

100

1000

0 200 400 600 800 1000 1200 1400 1600 1800 2000

top

bottom

anode

With 239 nm passband filter!!

V scans : two induction fields of 4kV/cm and 6 kV/cm

Double ThGEM M1 with CsIOn compass01, jarda/var/www/html/jarda/THGEMs - Trieste LAB activity/IV DOUBLE GEM

The double ThGEM M1 with CsI can’t stand the current produced by the D2 lamps, even the ORIEL at its minimum yield.So, the only measurement possible is the single electron spectrum.The light sources are two:• environment UV (the quartz window is uncovered)• D2 lamp filtered with the two band pass filters of 239 nm and 289 nm.The acquisition are of two kinds:•with autogate (series UV#) a large pedestal is observed•with external gate produced by the bottom signal (because of some spurious signals running the threshold is a bit high: ~ 4fC and this explains why we can’t reach the lower part of the spectra)

Double ThGEM M1 with CsIsingle photoelectron spectra

1

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100

1000

10000

0 10 20 30 40 50 60 70 80

charge (fC)

cou

nts

1

10

100

1000

0 5 10 15 20 25 30 35 40

charge (fC)co

unts

With autogate With external gate

• V2 & induction fixed• V1 & transfer scans

Triple ThGEM C7 @ CERNWe measured essentially the double ThGEM (the top two ThGEM),keeping the anode and bottom 3 @ GND, and using as “anode” the top 3.The currents are read out by the picoammeters.The signal source is a 164 Hz 55Fe.

Drift scan:for Edrift > 1kV/cm, practically all the charge is collected inside the holes of the first ThGEM:all measurements performed with a drift field of 1kV/cm (500V).\

Note that, when the V1 is low, the

field lines from cathode to TOP1 are

stronger and more electrons go to

TOP1

drift scan

0

50

100

150

200

0 1 2 3 4 5 6

E drift (kV/cm)

Hz

1200 V

DV 1 = 1100 V

1000 V

1225 V

Triple ThGEM C7 @ CERNV1 and V2 scans

D V 1 = 1300 V

1

10

100

1100 1150 1200 1250 1300 1350 1400

D V 2

pA

anode

bottom 2

top 2

The currents of all electrodes are measured: because of the non ideality of the picoammeters, just non negligible currents can be measured.Then drift, top1, bottom1 currents are readable just for high gains

and, when it happens, all currents sum to zero!!

scans done for two induction fields: 3kV/cm (480 V) and 2kV/cm (320 V).

D V 2= 1300V

10

100

1100 1150 1200 1250 1300 1350 1400

D V 1

pA

anode

bottom 2

top2

Triple ThGEM C7 @ CERN charge sharing between “last bottom” and “anode”

induction scans

ratio (DV 1 = 1300 V)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

0 1 2 3 4 5 6

induction field (kV/cm)

rati

o

DV 2 = 1200 V

1250 V

1300 V

1350 V

Drift = 1kV/cm (fixed) – transfer = 2kV/cm (fixed)

ratio (DV 2 = 1300 V)

0%

10%

20%

30%

40%

50%

60%

70%

80%

0 1 2 3 4 5 6

induction field (kV/cm)

rati

o

DV 1 = 1200 V

1250 V

1300 V

1350 V

DV 1 fixed = 1300 V, so the same amount of charge arrive at the second ThGEM, the sharing is in this case independent of the gain…

DV 2 fixed = 1300 V, so different amount of currents arrive at second ThGEM: more current comes, more goes to the anode

Triple ThGEM C7 @ CERN

triple (not stable)

0

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0 100 200 300 400 500 600 700 800

charge (fC)

double

0

10

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30

40

50

60

0 100 200 300 400 500 600 700

charge (fC)

55Fe spectra acquired with the maximum gain:

charge ~300 fCGain = 8.5k

for both double and triple ThGEM.

the triple ThGEM is not stable!At this high gain…