a m , less than30.4, which were ignited by the o p i n g ofthe ewere i n & & fbr eight kinds of electrode mataials 7he Dc cx" ofthe arc voit#s showed pearliar values tothe mataials but 6queni spike. voltages appeared together with the decreae of the arc (XIITeld ( i i i t i t y ) . The i " i i of the irstabity differed depend on the elechDde mataial and it was c"ed that the waveform of the spike voltage was the same wim the voltage drop of the inductive resislance of the eirarit The spike voltage may ignite an oscillation of the arc amend as a result of U: of the circuit The osciliatim w m obsaved by adding a pnauel opacifance and a Saies "xtotheeiradtandthewawavefiamsoftheoscillation agreed well with the simulated w a v e h . Arc voltagg and w i t i e s of low current E€ VaRlWn c m w , coppero, zinc(2nx ms@dw m) and w p p e r k ( W s m ) auoy wee lsed me cafbde was k e d to thechambaarid the anode could move horizantally by a Stepping motor wilh a velocity of 5 d s .Befae the o p i n g ofthe elecbodes, a dc current in the range IO to 30A was set duough he electrodes and an im:ignites by the opening of the elechodes.The arc vdtages were md wing a 1/1ooO high voltage pd~~!, T&JOII~X M 1 5 , bandwidth of dc to 75MtIz and an oscilloscope, Y&ogbwa DL 1540, banhvidth of dc and the oscillcscope. One is Sony Teldronix d d c " I pmbe A63O3, banhviwl ofdc to 15Mz and andha is a handn%& Ro@dti i d , bandwidth Of 4 W to SoMHz Ilwawed to 1mMHZ A x amem were ~d u S i n g t w 0 pobes ==% d Y high 6quency c o m w by the Rogowski coil.

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