The Design and Characteristics of Highly Ionized Hydrogenous Laboratory Plasma Sources

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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) .

“…Studies of image converter framing camera pictures show that at about 100 ILsec after plasma formation turbulence has virtually disappeared (Brennan et al 1963) .…”

Section: Theorymentioning

confidence: 99%

Section: (A) Plasma Preparationmentioning

confidence: 99%

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

Brand¹,

Heckenberg²,

Watson-Munro³

1969

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“…3), which has been described in detail by Brennan, Lehane, et al (1963). It consists of a stainless steel vacuum vessel, through which hydrogen at a pressure of 70/LmHg is circulated.…”

Section: Experimental Methods (A) Apparatusmentioning

confidence: 99%

Some Experimental Observations of the Attenuation of Alfven Waves in a Laboratory Plasma

Brown¹

1965

SummaryAn experiment is described in which the velocity and attenuation of torsional, azimuthally symmetric, hydromagnetic waves are measured in a hydrogenous plasma, from low frequencies where ion-neutral collisions are unimportant to the wave damping, to frequencies where such collisions profoundly affect the damping. A theory including both ion-electron and ion-neutral collisions is outlined, and the attenuation results are compared with the theoretical values. An estimate is made, from the frequency dependence of the attenuation, of the hydrogen ion-atom collision cross section for momentum transfer.

“…The plasmas used in these interferometry studies were produced in the cylindrical metal vessels of the Supper I (diameter 15 cm) and Supper II (diameter 21 cm) machines at Sydney University, by the discharge of a pulse-forming network between the cylinder and a short central electrode at one end of the machine (Brennan et al 1963). The resulting plasma was transient in nature and was contained by a strong axial magnetic induction field for some hundreds of mioroseconds.…”

Section: Merferometersmentioning

confidence: 99%

Microwave Interferometry for Plasma Studies

Robinson¹,

Sharp²

1963

A beam of microwave radiation is a powerful and penetrating means of exploring the density and temperature oflaboratory plasmas while causing minimal perturbation of the plasma. To a wave of frequency greater than the electron plasma frequency the plasma behaves like a dielectric, causing a change in the "optical" path which, when measured by interference techniques, yields the average electron density. The attenuation of the probing wave can give the collision frequency and hence the plasma temperature. Propagation EquationsRepresenting a plane wave by the notation eiwt-yr we can determine the propagation constant y from the well-known Appleton-Hartree dispersion relation. If we restrict consideration to the case of propagation transverse to the confining magnetic induction field with the E-vector of the wave parallel to this field, the dispersion relation is given bywhere v is the collision frequency. For the plasma used in these experiments v is much less than the wave frequency wand the plasma frequency wp = (nee2/~ome)t.In the three frequency regions of interest, w>wp' w = wp' and w< wp' the attenuation constant a and the phase constant (3 are found from equation (1):(3 = (w~v/2cw2) (w~/w2_1)-t.(I)) Equation (3) gives the electron density in terms of the measured phase shift and (2) gives the collision frequency from the measured attenuation and known density. Provided the electron-ion collision frequency is somewhat. larger than the electron-neutral gas collision frequency the electron temperature (Te' in degrees Kelvin) can be calculated from the expression (Delcroix 1960) v = (2·6n In A)jTe3/2, collisions/s,