Production and Study of an Alkali Plasma with Negative Ions

Abstract

The method of contact ionization is used to produce a three-component plasma (Cs+, Cl-, e-) in the Q-device BARBARA using a beam of Cesium chloride. The end-plate temperature controls the concentration of Cl-, which can be varied in a wide range. The density of negative ions is obtained from the difference between the positive ion density given by a Langmuir probe and the electron density given by a microwave resonator. A high concentration of negative ions is achieved.

Recombination of Alkali Plasma Ions on Hot Tungsten Surfaces

“…4 Experiments have been designed to test this theory by comparison of equilibrium densities and ion input flux. 5 "" 8 Rough agreement between theory and experiment has been found at high density, where there is no electrostatic potential to confine ions inside the plasma column. However, at low densities, where a potential barrier between plasma and hot surfaces should reduce the ion surface losses, the measured loss rates are more than an order of magnitude greater than predicted by theory 0 In this paper, we report the direct measurement, by means of a Langmuir-Taylor detector, of the escaping flux of recombined atoms from one hot tungsten end plate of the Q-3 machine in contact with cesium and potassium plasma.…”

“…On the basis of evidence obtained from plasma profiles, one group has concluded that the anomalous losses occur at the hot end plates. 18 Others, on the basis of measurements with radial ion flux collectors, tend to favor a radial loss interpretation. 19~21 From Fig.…”

“…The solutions to Eqs. (7) and (8) in the low-density regime are given in the figure, for assumed ion lifetimes of 60 and 30 msec. It is evident that r = 60 msec provides a good fit to the experimental data.…”

“…The loss time T strongly influences both the ion temperature and the end loss rate from Eqs. (7) and (8). It is instructive to consider the predictions of the equations for two extreme situations.…”

“…ei w to (8) where I is the length of the plasma column, T w is the wall temperature, r{ 0 is the ion charge-exchange time, and r ^ is the electron-ion equipartition time. From Eq* (8) the excess energy imparted to the ions entering the plasma is dissipated by cooling of energetic ions striking the hot end surfaces (first term on the right-hand side), by radial energy loss (second term), by ion-electron collisions (third term), and by ion-neutral charge-exchange collisions (fourth term).…”