Edda Gschwendtner1

RF test of a small TPG detector prototype

F. Ambrosino,C. D’Addio, F. Caspers, U. Gastaldi, E. Gschwendtner, E. Radicioni, G. Saracino

Edda Gschwendtner2

TPGino

3

1

2

1

Distance

mmcathode

GEM1

GEM2

GEM3

PAD

10

Drift

T1

T2

Induction

Drift field: 3 kV/cm T1=T2 field: 3 kV/cm Induction field: 5 kV/cm VG1= VG2= VG3=315 V Total gain ~ 5x103

Triple GEM prototype designed and assembled at LNF (G. Bencivenni et al.)

GEM 10X10 cm2 standard geometry CERN

40 PADs 2.5x1cm2

50 m kapton cathode + 5 m copper 20 m aluminized mylar gas window HARP preamplifier

Gas: Ar:CO2 80:20

55Fe source (5.9 keV)

Edda Gschwendtner3

Detector

Inside a 2 mm brass shielding:

detector

preamplifier

HV distributor boards

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RF test area at LINAC 3

GEM DETECTOR RF power supply

202.56 MHz

Power (kW)

Emax

(MV/m)Len.(m)

IA2 250 15 1.5

IA3 285 11.5 2.2

RF pulse: 0.6 ms period of ~1.2 s

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RF test setup

GEM DETECTORGEM DETECTOR

H.V. power supplyH.V. power supply L.V. power supplyL.V. power supply detector to RF tanks ~30cm

Detector back to RF power supply ~1m

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RF field measurement

Agilent-HP 11955A biconical antenna

to measure the RF field close to the detector area

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RF field measurement

0.6ms

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E-field from RF measurements

With the known antenna factor AF and the signal VO of the RF from the antenna measured by the oscilloscope we calculated the electromagentic field E:

AF(200MHz) = 16.7 dBm-1 V0=3 V

AF= E(Volt/m)/ VO(Volt)

20 log10 E(Vm-1) = 20log10VO (V) + AF(dBm-1)

E(Vm-1) = 10(logVo + AF/20) = VO10AF/20

E=20 V/m

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Noise response of the detectorNoise response of the detector (no HV on GEM)

Before shielding and grounding: ~400 mV peak to peak inside the RF pulse

After shielding and grounding: ~20 mV peak to peak outside the RF pulse ~ 80 mV peak to peak inside the RF pulse

With HV on the GEM:Noise response stays the same! RF no influence on detector, only on electronics, cables, etc…

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Detector response to 55Fe X-ray55Fe source: 5.9 keV peak and 3 keV escape peak.GEM working voltage: 3x315 VRF ON!Self-trigger

55Fe spectrum Background spectrum

Nb. This takes away one of the main worries:There is no sign of the photons hitting the GEMS)

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Detector response to 55Fe during RF pulse

Zoomed signal

55Fe sourceGEM working voltage: 3x315 VTrigger: RF signal from the antenna

55Fe pulse height: ~300mV

Noise: ~40mV!

signal

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Conclusion We tested a GEM based detector, with cables and grounding

not optimized for RF immunity, in the vicinity of the CERN LINAC 3 accelerator (2 RF accelerator tanks of 200 MHz, power supply of ~ 250 KW).

The noise response of the detector can be improved by a factor ~5 (400mV/80mV peak to peak) with home-made shielding of the cables, electronics, etc.

More effective and professional shielding can be provided in the MICE setup. Proof of concept is anyway valid.

The signal to noise ratio of a 55Fe X-ray source is ~8 (300mV/40mV) when the RF is on!

We were able to shield a GEM detector setup such that the presence of RF field at the order of E=20 V/m did not significantly increase the detector noise.

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TPC active volume

Solenoid coilField cage and support

Sketch-example of shielding principle for final chamber. (need to understand interference with steel shielding for PMTs etc..)All except field cage can be tested in situ early spring.

Shielding can

flexesPre-amps