Digest of literature on dielectrics (1970)

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160 ELECTRICAL BREAKDOWN OF GASES (67) with mixtures of O2 and HgO, six kinds of 10ns with different mobilities were found, and Eichmeier and Herden (68) showed mobility spectrograms of art i f icial ly produced atmospheric 10ns measured with an aspiration-type mobility spectrometer. Hantzsche (69) considered for a static electric f ield a one-dimensional model of the motion of ions, controlled solely by charge exchange (electron capture f r o m gas molecules). Solutions of the kmetic equations for 10ns and fast neutrals were derived in several special cases. D r i f t velocities and reactions of mtrogen 10ns have been investigated by McKmght et al . (70) at values of E / N between 1, 5 and 20 x 10-^6 V cm2, and at pressures between 0. 5 and 1 Tor r . The ions in nitrogen were found to occur in two groups, N2'''-N4''" and N -̂N3''", such that interactions within the groups are much faster than any interactions between the groups. Orient (71) measured the mobility of atomic and molecular helium 10ns for temperatures between 195°K and 665°K, and Saporoschenko (72) reported the mobilities of CO"*", 002"*", and 0202"*" 10ns in carbon monoxide over an E/p range f rom 15 to 180 V cm~l T o r r~l. Dr i f t velocities of mass- identified positive 10ns in air have been measured by Sinnott et a l . (73) as a function of E / N for 2 x 10-16 S E / N ^ 2 X 10-14 v c m ^ " and for 1. 8 x l o l ^ ;S N ̂ 7 x 10l5 cm-3. These measurements lead to values of the zero-field mobilities of 1.6, 3.5, and 2. 5 cm^/v sec for N2"*', NO"*", and 02"*", respectively, in air . U n i f o r m F i e l d Breakdown Bartmkas (74) found that for helium gaps between 0.15 and 2. 50 mm the discharge process exhibited features common to both spark and glow discharges, and Betts and Davies (75) measured formative time lags in hydrogen of the order 10 nsec for pressures up to 50 Torr and for 50 < E/p < 500 V cm-1 T o r r " l , Beynon and Llewellyn-Jones (76) concluded that the cold electron emission f rom mckel electrodes in mtrogen was produced by positive 10ns liberating electrons f r o m the cathode subsequent to their neutrali- zation in Auger processes, Bortnik (77) described a theoretical and experimental investigation of the statistical and volt-second characteristics of the breakdown of an electrical discharge in helium. The relative roles of various experimental processes in

UNIFORM FIELD BREAKDOWN 161 supporting the discharge as a function of the product pd and the f o r - mative time lag were examined. Bychkova et al . (78) reported ob- servations on the voltage drop in a spark at E/p ratios between 10^ and 10^ V cm"-'̂ T o r r ' ^ , and Chernyak and Natanson (79) gave an outline description of equipment for measuring the frequency dis- tribution of amplitude (20-20, 000 Hz) m the sound emitted f rom a discharge between electrodes separated by a 1. 5-mm gap. D'Alessio and Lanza (80) analyzed the mechanisms of spark generation that produce luminous and electric pulses of the order of subnanoseconds m a gas at a high pressure and found that the classical mechanisns cannot explain the generation of I f l U electrons in 0.3 nsec, which was experimentally detected. The processes leading to breakdown in a pure N2 discharge were studied by Doran (81) by streak and shutter photography using image converter and intensifier techniques, and the results correlated with current, voltage, and photomultiplier measurements, in a plane-parallel 2-cm discharge gap under pressure of 300 Torr . An overvoltage of 7. 56% was applied to the gap, and the discharge was initiated by a uv flash which emitted ~400 electrons f rom a small area on the cathode. Under these conditions the imtial development of the spark took place by the Townsend mechamsm. After four generations a series of luminous fronts traverse the gap, increasing current to the ampere range, where a quasi-stable glowlike dis- charge formed. The processes occurring in the further transition to the constricted spark channel are reported. Dzoanh (82) showed that the permanent high-pressure discharge which has not been observed hitherto in a uniform electric f ield can be established if the lon-bombardment effect is replaced by the more efficient Malter-Paetow effect. EUmgton (83, 84) investigated the break- down voltage characteristics of alkali-metal-seeded rare gases at elevated temperatures and atmospheric pressure. Fischer and Gallagher (85) photographed the development of init ial spark channels and optical phenomena related to init ial electrode pro- cesses in a 4,000-A spark discharge of 20 nsec duration in 1 atm air, gap 0.85 mm, through a Kerr cell shutter. LeNy (86) con- firmed the effect of temperature on prebreakdown currents between parallel plates in air, N2, and CO2 under a pressure of some tens of bars and with various metal electrodes, and Maurel et a l . (87) calculated the space-time evolution of an avalanche accounting for the space charge constituted by an electron cloud. Mesyats and Korshunov (88) investigated breakdown for air gaps