Gas discharge characteristics in pure CH4 have been studied in the high gas-multiplication region by using a gas counter with a thick anode wire (50 μm in diameter) and compared with those of the self-quenching streamer (SQS) mode in a CH4Ar mixture. The results of the first optical observation indicate that the large pulses observed in CH4, whose pulse amplitudes are comparable to those of the SQS mode, are not due to streamer discharges. Instead, a luminous region is observed near the anode wire (r ≤ 0.7 mm) where the electric field is higher than the threshold value for gas multiplication, 104 V/cm.
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