Über die spektrumanlegung in funkenentladungen

Abstract

A short summary will be given, about the investigations on excitation processes in the spark-channel plasma made in the Physical Institute of the Academy of Sciences. The mechanism of spark-channel formation has to be considered as a kind of explosion. The discharge is followed by a cylindrical shock wave with a front causing the ionization and the extension of the spark channel. A hydrodynamical theory of this process was developed and the velocity of the channel extension, the current density, the distribution of the gas density in space and time, and the temperature in the discharge channel were verified experimentally with optical and electrical methods. The line intensities of lines of different ionization states and excitation energies show a different behaviour, enabling one to draw conclusions on the variation of excitation and ionization conditions. From the behaviour of the continuum it was concluded that it is connected with doubly ionized atoms. The measurement of the excitation temperature using the N II lines showed this temperature to be equal to the gas temperature, i.e. 40,000°. These experimental results were used in a thorough investigation of the fundamental excitation and ionization processes in the spark plasma. As a result we can state that the partition of the atoms over the excitation and ionization levels agrees with the Boltzmann and Saha equation using the electron temperature as a parameter and a relaxation time of about 10 −10 sec or 10 −7 sec. Thus the electron temperature may bo regarded as excitation and ionization-temperature. The major component of the channel plasma is doubly ionized nitrogen. The relaxation time of electron and gas ion temperature is taken as about 10 −7 sec. The conclusion is that a characteristic feature of the spark discharge is the high energy dissipated in the first stage of the discharge. This results in a shock wave, removing the gas from the region of the channel axis and causing a plasma of low gas density and high current density. The electron temperature of this plasma is very high and the ionization very strong, causing the “hot” character of the spark spectrum. This permits the use of the equations for the temperature equilibrium at temperatures of 40,000–50,000°.