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 cm 2 standard geometry CERN PAD readout: x1cm 2 50  m kapton cathode + 5  m copper 20  m aluminized mylar gas window HARP preamplifier Distance mm cathode 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 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

MHz Power ( kW) E max (MV/m) Len. ( m) IA IA detector window faced the RF tanks at distance ~30 cm The back was ~1 m distant frome the RF power supply GEM DETECTOR H.V. power supply L.V. power supply RF power supply heads

detector configuration Gas: Ar:CO 2 80:20 open mode fields and gain : –Drift field: 3 kV/cm –T1=T2 field: 3 kV/cm –Induction field: 5 kV/cm –  V G1 =  V G2 =  V G3 =315 V –Total gain ~5x Fe source (5.9 keV x) Distance mm cathode 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 V O of the RF from the antenna measured by the oscilloscope we calculated the em field E: AF= E(Volt/m)/ V O (Volt) 20 log 10 E(Vm -1 ) = 20log 10 V O (V) + AF(dBm -1 ) E(Vm -1 ) = 10 (logV o + AF/20) = V O 10 AF/20 AF(200MHz) = 16.7 dBm -1 E-field calculation V O = 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 ray Using a 55 Fe 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 was acquired 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.

55 Fe 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  V GEM =315x3 V. X out of coincidence X in coincidence Signal zoom

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.