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UBC Theses and Dissertations

Magnetically stabilized helium arc for scattering experiments Potocnik, Vinko

Abstract

For verifying some theoretical predictions of light scattering from magnetized plasmas, a stable pulsed helium arc discharge in a magnetic field up to 5 Teslas has been built. The arc has been investigated at filling pressures of 2 to 5 torr and plasma currents between 1 and 5 kA. Plasma parameters were measured at a magnetic field of 4 Teslas and a pressure of 3 torr. At these values of the magnetic field and the filling pressure the arc is steady and approximately cylindrically symmetric up to a plasma current of 2.8 kA. Time dependence and radial distribution of the electron density and temperature have been determined from spectroscopic measurements, 1aser•interferometry, and laser scattering. The latter two techniques were used successfully for the first time on a magnetically stabilized arc to measure the electron density and temperature in the hot core of the arc. The axial electron density is 1.2 x 10¹⁶ cm⁻³ and is approximately constant over the arc cross-section in the high temperature region as predicted by theory. The axial temperature is 145,000°K. Thus the arc design and the plasma properties are suitable for scattering experiments. The arc behaviour is governed by dynamic processes which depend on the geometry of the apparatus. In order to show the problems of the design and operation of the apparatus, the theory of arc behaviour in a magnetic field is outlined.

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