Plasma Effects on the Metastable Neutral HYDROGEN(2S) Atom.

Atomic radiative processes which occur in plasmas have long been of interest of plasma physicists. The process we are investigating is atomic dipole transitions, specifically transitions from the metastable 2s to the 2p in hydrogen, which are induced by processes which occur in the plasma. An experiment was done to measure the rate of transitions from 2s to 2p in hydrogen. This experiment was divided into two sections. The first was to measure the transition rate in a near equilibrium plasma. The second section measured the transition rate when RF oscillations were imposed on the plasma. The results of the first part of the experiment show that microscopic fluctuating electric fields which are produced by the motions of the charged particles induce transitions from 2s to 2p in hydrogen. The magnitude of this effect is compared to predicted transition rates due to collisions with electrons and ions and to rates predicted for an equilibrium plasma. In the second part of the experiment, the plasma was shown to act as a filter, preventing transitions from being caused by the RF unless the RF was in the range where plasma waves could be launched. The interpretation we give for this effect is that when the oscillations are inducing transitions, it is because plasma waves are being launched in the plasma and it is these waves which are inducing the transitions. These results have a couple of important applications. The results for the equilibrium part of the experiment can be used to explain a limit in the current which is produced by the Lamb-shift polarized ion source. The other important application is the possible use of the effect seen in the RF case as a non-perturbing diagnostic for plasma waves. Since dipole transition rates are proportional to E('2) and very sensitive near resonance, this effect could prove to be more accurate and more sensitive than methods currently used.