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RF test of the GEM detector prototipe

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.

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RF test of the GEM detector prototipe

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  1. RF test of the GEM detector prototipe F. Ambrosino,C. D’Addio, U. Gastaldi, E. Gschwendner, E. Radicioni, G. Saracino • Detector description • RF test area(LINAC3) • detector working conditions • RF field measurement • Detector measurements • Conclusions

  2. Triple GEM Detector mylar gas window Distance mm 10 cathode • Triple GEM prototipe designed and assembled at LNF (G. Bencivenni et al.) • GEM 10X10 cm2 standard geometry CERN • PAD readout: 40 2.5x1cm2 • 50 mm kapton cathode + 5 mm copper • 20 mm aluminizedmylar gas window • HARP preamplifier 3 Drift GEM1 1 T1 GEM2 T2 2 GEM3 1 Induction PAD

  3. The detector is inside a 2 mm brass shielding with preamplifier and H.V. distributor boards

  4. The RF test area The 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

  5. detector window faced the RF tanks at distance ~30 cm The back was ~1 m distant frome the RF power supply H.V. power supply L.V. power supply GEM DETECTOR RF power supply heads

  6. Distance mm 10 cathode 3 Drift GEM1 1 T1 GEM2 T2 2 GEM3 1 Induction PAD 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)

  7. RF field measurement We used a Agilent-HP 11955A biconical antenna to measure the RF field close to the detector area

  8. The RF pulse is 0.6 ms long with a period of ~1.2 s

  9. E-field calculation 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 VO = 3 V E= 20 V/m

  10. 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

  11. Detector response to x ray Using 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 V Most of the events are out of coincidence with respect to the RF pulse.

  12. 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 DVGEM=315x3 V. X out of coincidence X in coincidence Signal zoom

  13. Conclusions We 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.

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