Ionic Waves Research Articles

ON THE APPLICATION OF PLASMA KINETIC THEORY TO IONIC SOUND-WAVE EXPERIMENTS IN MAGNETIC FIELDS

The kinetic theoretical results for a homogeneous plasma in a uniform magnetic field are discussed qualitatively. The role of the mean cyclotron radius as a natural long-range cutoff is clarified. A relationship between a critical frequency for ionic sound waves and the magnetic-field intensity is predicted.

Measurements on ionic waves amplified by collective behaviour in an alkali plasma

An experiment on ionic waves sustained by collective amplification in a uniform, steady plasma, free of electric field, is described. The plasma is obtained by contact ionization of caesium or potassium vapours on the surface of two coaxial tantalum cylinders kept at a temperature of about 2600 °K. The application of a variable D.C. voltage between the two cylinders gives rise to an unstable velocity distribution function which can be varied at will. Predictions are given for the dependence of the frequency of the oscillations on the applied voltage, on the ionic mass and on the plasma density. Experimental results are consistent with the predictions if the wavelength is equal to four times the distance between electrodes. A possible explanation of this fact is also suggested.

Propagation of Ionic Magnetohydrodynamic Waves

Ion waves in a plasma, in the presence of a magnetic field, generally exhibit simultaneous transverse and longitudinal oscillations. The velocity of these “modified ion waves” depends primarily on the mass and temperature of the charged particles and on the direction and magnitude of the magnetic field. In a weakly ionized gas, the attenuation of these waves is mainly determined by the ion-neutral and electron-neutral collision frequencies. For a transverse magnetic field, wave propagation is only possible at frequencies larger than the geometric mean of the ion and electron cyclotron frequencies. Theoretical and experimental results on velocity and attenuation of ionic magnetohydrodynamic waves are described.

Ionic Waves in a Plasma Generated by an Electron Beam

Some experimental results are shown for ionic plasma waves formed by an ionizing electron beam in magnetically confined plasmas. (R.E.U.)

Observations of Ionic Sound Waves in Plasmas: Their Properties and Applications

This paper discusses extensive experimental studies of the ionic sound waves predicted by Tonks and Langmuir. Self-excited oscillations have been observed both in magnetically supported plasma columns and in spherical discharge tubes. The fundamental frequency and the overtones of each system agree with those predicted by the ionic-sound-wave formula in terms of the electron temperature, the ion mass, and the dimensions of the system. A simple equation is used to predict when damping by the neutral gas prevents a given mode of plasma oscillation from being observed. The thermal electron pressure, required for the existence of an ionic sound wave, has been measured mechanically. Resonance effects have been observed between the ionic-sound and the ion cyclotron frequency in the magnetically supported plasma column. Practical applications of ionic sound waves are as follows: The electron temperature of a plasma was found by measuring the frequency of a standing ion-wave mode. The neutral gas density was estimated by observing the gas damping of various standing ion-wave modes.

Observations of Ionic Sound Waves in Plasmas

Standing ionic sound waves are observed in plasmas in cylindrical and spherical discharge tubes. H, He, Ne, hr, Kr, and Xe are used. As many as 4 harmonics are observed for one gas. (T.F.H.)