We report an experimental method for timespace resolved measurements on a dense, extreme-temperature, plasma in a theta pinch by observation of Faraday rotation of 3.39jU infrared He-Ne maser radiation. Since the rotation is proportional to B, this method affords a powerful technique for measuring B in pure, fully ionized, hydrogenic plasmas as occur in controlled fusion research when electron density n is determined independently. A unique feature of the method is the successful utilization of a low-power (2-mW) CW gas-phase maser to extreme temperature plasma diagnostics. Seven degrees of rotation along the central axis are observed at the 3.5-jLtsec, 50000-gauss, peak field compressing fully ionized deuterium at an initial electron density of 6xl0 15 /cm 3 , and immersed in a 4500-gauss forward bias field. The results confirm earlier considerations 1 ' 2 and expectations that the coherence, monochromaticity, and low beam divergence properties of infrared and optical masers could be effectively utilized for magnetoplasma diagnostics.The experimental arrangement, found to be highly versatile and accurate, is shown in Fig. 1. 2 mW of 3.39/n linearly polarized radiation is delivered in the output beam of the He-Ne gas- SPHERICAL MIRRORphase maser which utilizes a metal-coated spherical mirror and a silicon flat for the infrared resonator. A first pair of flat and spherical mirrors focuses the beam to less than 1-mm diameter at the center of the theta-pinch plasma tube. A second pair of flat and spherical mirrors directs the emerging beam in turn through a 3.39-IR narrow band pass filter, and iris, and focuses it onto a polarization analyzer. The second spherical mirror provides compensation for beam refraction that is observed to occur due to radial electron-density variations. A time-resolving infrared polarization analyzer for the 2-to 4-micron range was developed for this investigation. 3 The instrument employs two Brewster-angle, air-germanium interfaces positioned such that the parallel and perpendicular components of the polarized radiation are directed onto two separate uncooled InAs photovoltaic detectors. Angular resolution of approximately 0.5° for polarization oscillations as high as 1 Mc/sec is obtained for 0.5 mW into the analyzer. In this application the analyzer is positioned at 45° relative to the nonrotated polarization to provide equal intensity onto the detectors. The preamplified detector outputs are both added and subtracted, with the sum S(t) and difference D(t) simultaneously displayed on the dual-beam oscilloscope. As Faraday rotation is effected by the plasma, the angular rotation 0 r is given by (t)=Urcsin[D(t)/S(t)] r a)FIG. 1. Faraday-rotation arrangement for IR maser diagnostics of theta-pinch plasma.Deuterium is initially fully ionized within the 20-cm length, 5-cm ID, coil by super high-power 50 MW preheating at 1.5 Mc/sec. 4 A forward or reverse B 0 bias field to 10 kG is provided. magnetic compression is achieved by 3.5-jusec rise to a peak as high as 75 kG. 5 156

Profiles of nine lines of singly ionized nitrogen have been measured in a dense (Ne= 1.9 && 10 cm ) high-temperature (22 800 'K) plasma produced behind the reflected shock wave in a T tube. Measurements were carried out that verified the fact that the plasma was homogeneous in both the radial and the axial directions and that the plasma was optically thin at the various wavelengths where the profiles were measured. The half-widths of the measured profiles show large discrepancies with earlier reported measurements of Day and Griem and, in most cases, show significant disagreement with the theoretical predictions.

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A polarization analyzer for time-resolved rotation measurements of polarized infrared radiation from 2- to 4-μ wavelength is described. The instrument employs air-germanium interfaces, uncooled InAs photovoltaic detectors, and 10-Mc-bandwidth low noise preamplifiers. Angular resolution of approximately ½° for polarization oscillations as high as 1 Mc is obtained for ½-mW emission from a He-Ne maser at 3.39 μ. It is useful, with reduced resolution, up to 10 Mc; the resolution can be improved through reduced preamplifier bandwidth for below 1 Mc. Application of the instrument to measurement of the Faraday rotation of a 3.39-μ polarized maser beam propagated through a dense, high temperature, deuterium plasma in an intense magnetic field is discussed.