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RF test of the GEM detector prototipe. F. Ambrosino,C. D’Addio, U. Gastaldi, E. Gschwendner, E. Radicioni, G. Saracino. D etector description RF test area (LINAC3) detector working conditions RF field measurement Detector measurements Conclusions. Triple GEM Detector. - PowerPoint PPT Presentation
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RF test of the GEM detector prototipe
• Detector description• RF test area (LINAC3)
• detector working conditions
• RF field measurement
• Detector measurements
• Conclusions
F. Ambrosino,C. D’Addio, U. Gastaldi, E. Gschwendner, E. Radicioni, G. Saracino
Triple GEM Detector
• Triple GEM prototipe designed and assembled at LNF (G. Bencivenni et al.)
• GEM 10X10 cm2 standard geometry CERN
• PAD readout: 40 2.5x1cm2
• 50 m kapton cathode + 5 m copper
• 20 m aluminized mylar gas window
• HARP preamplifier
3
1
2
1
Distance
mmcathode
GEM1
GEM2
GEM3
PAD
mylar gas window
10
Drift
T1
T2
Induction
The detector is inside a 2 mm brass shielding with preamplifier and H.V. distributor boards
The RF test areaThe detector was placed near the two 200 MHz accelerator tanks IA2 and IA3 of the heavy ions accelerator Linac3 at CERN
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
detector window faced the RF tanks at distance ~30 cm
The back was ~1 m distant frome the RF power supply
GEM DETECTORGEM DETECTOR
H.V. power supplyH.V. power supply L.V. power supplyL.V. power supply
RF power supply headsRF power supply heads
detector configuration
• Gas: Ar:CO2 80:20 open mode
• fields and gain :– Drift field: 3 kV/cm– T1=T2 field: 3 kV/cm– Induction field: 5 kV/cm VG1= VG2= VG3=315 V– Total gain ~5x103
• 55Fe source (5.9 keV x)
3
1
2
1
Distance
mmcathode
GEM1
GEM2
GEM3
PAD
10
Drift
T1
T2
Induction
RF field measurement
We used a Agilent-HP 11955A biconical antenna to measure the RF field close to the detector area
The RF pulse is 0.6 ms long with a period of ~1.2 s
Using the known antenna factor AF and the signal VO of the RF from the antenna measured by the oscilloscope we calculated the em field E:
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
AF(200MHz) = 16.7 dBm-1
E-field calculation
VO = 3 V E= 20 V/m
Detector response to the noise
After shielding and grounding the noise response of the detector was~20 mV peak to peak outside the RF pulse~ 80 mV peak to peak inside the RF pulse
Detector response to x rayUsing a 55Fe source we measured the response of the detector to 5.9 keV x rays. A spectrum was acquired using a MCA showing the 5.9 peak and the 3 keV typical “escape” peak.A background spectrum wasacquired in the same condition but without the source.Working voltage 3x315 VMost of the events are out of coincidence with respect to the RF pulse.
55Fe x in coincidence with the RF Using the RF signal from the antenna to trigger the scope we looked for x inside the .6 ms window of RF pulse
VGEM=315x3 V.
X out of coincidenceX in coincidence
Signal zoom
ConclusionsWe tested a GEM based detector, with cables and grounding not optimized for RF immunity, in the vicinity of the CERN LINAC3 accelerator.
The detector worked properly close to 2 RF accelerator tanks of 200 MHz and their power supply of ~ 250 KW. The signals from a 5.9 keV x are clearly visible above the RF background.
GEMs don’t seem to suffer particulary from the presence of RF noise.