A TENTATIVE EXPLANATION FOR THE DISCHARGE PROPAGATION
Fabio Sauli
GDD Meeting 11.5.16
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P. Gasik
1-GEM setup
ED=400 V/cm
DVD=1120 V
VGEM=403 V
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1500 V/cm
300V
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IONS-INDUCED FEEDBACK?
GEM DISCHARGE
SECONDARY EMISSION FROM GEM TOP
I+ + Cu -> I + e + Cu*
DISCHARGE PROPAGATION
PROBLEMS:
HARD TO EXPLAIN PROPAGATION DELAY
LOW SECONDARY EMISION PROBABLILIY
VERY LOW FIELD ON GEM TOP AFTER DISCHARGE
NO GAIN IN GEM (VGEM ~ 0)
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ELECTRON DRIFT VELOCITY
Ar-CO290-10
ELECTRON DRIFT TIME
28 mm DRIFT GAP
400 V/cm
0.8 µs
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GEM ELECTRON TRANSPARENCY - LOW VOLTAGE
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F. Sauli, L. Ropelewski and P. Everaerts, Nucl. Instr. and Meth, A560(2006)269
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8.0
7.5
7.0
eV
21% CO2
QE of METALS
10-2
Cu WI ~ 4.5 eV (275 nm)
M,M, Fraga et al, NIMA323(1992)284
VUV PHOTON EMISSION IN DISCHARGES
SELF-QUENCHING STREAMERS IN Ar-CO2 MIXTURES
CO2 ABSORPTION CROSS SECTION
10-3
10-4
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J. Seguinot et al, NIMA297(1990)133
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GEM DISCHARGE
PHOTON EMISSION
109-1010 e-I+
PHOTOELECTRONS DRIFT
108-109 g
PHOTOELECTRIC
ON CATHODE
106-107 e
LOW FIELD GEM TRANSMISSION
STRONGLY DEPENDENT ON ED
~ 1µs
1 TO 50 µs
f(EIND)
RAETHER LIMIT EXCEEDED
IN INDUCTION GAP
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PROPAGATED DISCHARGE
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MAKES SENSE...BUT WHAT ABOUT ALL OTHER OBSERVATIONS
(DIFFERENT GASES, MULTI-GEMS,......)
COMMENTS AND SUGGESTIONS WELCOME
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