@article{oai:nagoya.repo.nii.ac.jp:02001768,
 author = {SHINOHARA, Ukichi},
 issue = {2},
 journal = {Memoirs of the Faculty of Engineering, Nagoya University},
 month = {Feb},
 note = {In the initial stage of spark discharge, space charge field is built up by the ionization by collisions of casual electrons in the atmosphere. Space charge field for an impulse spark is in a faint bluish filamentary form, but space charge for D.C. spark is diffused over the whole space between the spark gap. It is important to note that the space charge field of positive ions is prepared first, and procedure for building up of space charge field within the gap as well as ion density and its distribution within the gap must be considered. As the voltage rises, electron avalanche from cathode advances toward the anode along the space charge field. When the electron avalanche from cathode continuously propagates in the space charge field and reaches the anode, the spark breakdown occurs. At the voltage lower than the breakdown value, the electron avalanche from cathode does not continue to the anode ; it diffuses in the gap and acts as if it were a free electron. Hence, casual electrons and ions within the gap increase with the rise of voltage. If a positive electrode is placed in this space charge field, and its potential becomes high enough to accelerate a casual or free electron within the gap to the positive point and is able to ionize gas molecules near it, a brightly luminous canal is built up at the positive electrode which proceeds toward cathode as voltage is raised. That is, the positive canal consists of positive streamer produced previously and electron avalanche due to free electron also previously produced within the gap, as stated above. The canal becomes a luminous channel and changes the appearance from an impulse spark to D.C. spark. The degree of brightness depends on the electron density within the channel. Mobility of positive ion is very low and it plays the double role of building up a space charge field and a plasma state using electron of electron avalanche from cathode. If electron density in the plasma amounts to about 108 electrons per cm3, the plasma becomes a conductive path where the crossing of two electrodes means that a highly ionized channel has been formed joining two electrodes. Creation of this channel constitutes spark breakdown. The spark breakdown condition can be written (Emin+Er)∙e∙λ≧Vj∙e where, Emin ; minimum field strength of applied field in the spark gap, Er ; space charge field strength at tip of an electron avalanche, e ; electron charge, λ ; mean free path of electron in gas, Vj ; ionization potential of gas molecule.},
 pages = {201--240},
 title = {Experimental studies on the mechanism of electric spark discharge},
 volume = {9},
 year = {1958}
}