Spectral and Microwave Studies of the Decay of a Highly Ionized Hydrogen Plasma

Abstract

SummaryThe decay of an almost fully ionized hydrogen plasma immersed in a magnetic field of 1 tesla has been investigated spectroscopically and with microwave interferometers at 35 and 120 GHz. It has been found that the plasma decays approximately exponentially in time and that the density-temperature relations in the contracting central column are adequately described in terms of the theoretical predictions of Bates, Kingston, and McWhirter down to densities of about 1 X 1019 m-3 and temperatures of 2000oK. Competing processes of axial and transverse diffusion have been shown to play no significant part in the decay of this plasma. I. INTRODUOTIONThe ways by which ionized plasmas decay are of considerable interest not only to those working in the field of gaseous discharge physics, but also to astrophysicists and upper atmosphere physicists. Some early experimental observations were reported by Kenty (1928) and theoretical calculations by Cillie (1932). The decay of laboratory hydrogenous plasmas has been studied by Lord Rayleigh (1944), Craggs andMeek (1945), Fowler andAtkinson (1959), Hinnov and Hirshberg (1962), Cooper andKunkel (1965), andIrons andMillar (1965). The first calculations that recognized the importance of three-body recombination were performed by D'Angelo (1961). Later calculations by Bates, Kingston, andMcWhirter (1962a, 1962b; subsequently referred to as BKM) included other decay processes besides three-body recombination. The experimental observations of Hinnov and Hirshberg (1962) have confirmed the calculations of D'Angelo for low density plasmas (n < 5 X 10 19 m-3 ). The denser plasma work (5 X 10 21 to 1 X 10 21 m-3) of Irons and Millar and of Cooper and Kunkel yielded results that agreed well with the theoretical predictions of BKM for a hydrogen plasma opaque to Lyman line radiation.In this paper we report recent studies of plasma decay, extending the work of Irons and Millar (1965) to low densities (10 18 m-3 ) and low temperatures (2000 0 K), and finding the same good agreement with the theoretical predictions of BKM. II. THEORYWe make the following assumptions (experimentally justified in our plasma): (1) Neglect of inertial forces. Studies of image converter framing camera pictures show that at about 100 ILsec after plasma formation turbulence has virtually disappeared (Brennan et al. 1963) .