1. 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

2. Edda Gschwendtner2 TPGino 3 1 2 1 Distance mm cathode 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   VG 1 =  VG 2 =  VG 3 =315 V  Total gain ~ 5x10 3 Triple GEM prototype designed and assembled at LNF (G. Bencivenni et al.) GEM 10X10 cm 2 standard geometry CERN 40 PADs 2.5x1cm 2 50  m kapton cathode + 5  m copper 20  m aluminized mylar gas window HARP preamplifier  Gas: Ar:CO 2 80:20  55Fe source (5.9 keV)

3. Edda Gschwendtner3 Detector Inside a 2 mm brass shielding: detector preamplifier HV distributor boards

4. Edda Gschwendtner4 RF test area at LINAC 3 GEM DETECTORRF power supply 202.56 MHz Power ( kW) E max (MV/m) Len. (m) IA2250151.5 IA328511.52.2 RF pulse: 0.6 ms period of ~1.2 s

5. Edda Gschwendtner5 RF test setup GEM DETECTOR H.V. power supply L.V. power supply detector to RF tanks ~30cm Detector back to RF power supply ~1m

6. Edda Gschwendtner6 RF field measurement Agilent-HP 11955A biconical antenna to measure the RF field close to the detector area

7. Edda Gschwendtner7 RF field measurement 0.6ms

8. Edda Gschwendtner8 E-field from RF measurements With the known antenna factor AF and the signal V O of the RF from the antenna measured by the oscilloscope we calculated the electromagentic field E:  AF(200MHz) = 16.7 dBm-1  V 0 =3 V 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  E=20 V/m

9. Edda Gschwendtner9 Noise response of the detector Noise 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…

10. Edda Gschwendtner10 Detector response to 55Fe X-ray 55 Fe source: 5.9 keV peak and 3 keV escape peak. GEM working voltage: 3x315 V RF 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)

11. Edda Gschwendtner11 Detector response to 55Fe during RF pulse Zoomed signal 55Fe source GEM working voltage: 3x315 V Trigger: RF signal from the antenna 55Fe pulse height: ~300mV Noise: ~40mV! signal

12. Edda Gschwendtner12 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.

13. Edda Gschwendtner13 TPC active volume Solenoid coil Field 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 flexes Pre-amps