Die Entwicklung der Elektronenlawine in den Plasmakanal,untersucht mit Bildverstärker und Wischverschluß

The application of high gain image intensifier and image converter streak shutter techniques to investigations of faintly luminous early stages of gaseous discharges discloses in some detail the development of electron avalanches into anode- and cathode-directed streamers as soon as the critical amplification (n≈10⁸) is attained in the gap. The velocities of both of the streamer branches were measured quantitatively as to the dependence on pressure (p), field (E/p) and gas (Nitrogen and various mixtures), typical values being 0.5 ... 1 · 10⁸ cm/sec. We find that streamer propagation is suitably described in a coordinate-system drifting with the electrons (driftvelocityv _? ≈ 1 · 10⁷ cm/sec) and that the way it depends on the discharge parameters suggests that ionization by electron impact (in the eigen-spacecharge distorted field) and photoionization are the determining effects. — The cathode-directed streamers show a considerable intensification and acceleration as soon as they are encountered by cathodic secondary avalanches, which however are obviously not essential for the initiation of the process in itself. — The streak images give also an impression of persisting excitation and ionization processes in the region of the streamer-paths and of the transition into the beginning of the bright spark, correlated with several ionizing fronts observed moving towards anode or cathode with velocities even >10⁸ cm/sec. (The paper includes also details of the gaseous near UV-radiation which was utilized for registration with image intensifier or converter, especially with respect to the decaytime of the excited states.) The results obtained are essentially a verification and to some extend completion of predictions made on the basis of early cloud chamber investigations.