A method of direct display of electron temperature, which uses three closely spaced Langmuir probes at constant biases, is presented. Ion components of probe currents, which are relatively large in magnetized plasmas, are subtracted in the probe circuit. Direct display of the local value of the electron temperature is possible without any sweeping to the probe voltage. The sources of error are known and their effect can be readily evaluated during the experiment. Measurements of electron temperature in a P. I. G. discharge in hydrogen is presented as an example of application of this method.
Attenuation of a surface wave is studied experimentally in an unmagnetized cylindrical plasma column sustained by the wave itself. The losses connected with the plasma creation are negligible and the wave propagation is described by the relations for the linear regime. It is shown that a simple theory of collisional attenuation, obtained by extension of the collisionless theory to the case of few collisions, predicts very well the dependence of the attenuation on the electron density, the electron collision frequency, and the geometry of the plasma column.
When temperature fluctuations are large in a plasma, the floating potential cannot be used to calculate electric fields. This note describes a method which allows the calculation of the plasma potential as a function of time from measured values of the electron temperature and the floating potential. An application of this technique to the evaluation of electric fields in a reflex discharge is briefly outlined.
A new HF device is described. It allows the production, without the use of a magnetic field, of long plasma columns from a small HF coupling structure situated at one end of the column. Its operation is based on the propagation of a cold plasma surface wave. This device can work (in argon for example) at pressures from 2 mTorr to 20 Torr with electron densities from 1010 cm-3 to 1013 cm-3, depending on plasma diameter and HF power. Typically, 80W of 500 MHz HF will produce a 25 mn diameter column of 1.8 m length. The plasma is quiescent (low electron density fluctuations), efficient (~ 100% absorbed power), and perfectly reproducible. It can be used as a substitute for a positive column, and some practical applications are foreseen in ion production, laser excitation, gas preionization and spectroscopic sources.
