0883-6272/86 $3.00 + .00 Copyright ® 1986 SUNSAT Energy Council SUBMILLIMETER WAVE PROPAGATION IN TOKAMAK PLASMAS C. H. MA, D. P. HUTCHINSON, P. A. STAATS and K. L. VANDER SLUIS Physics Division Oak Ridge National Laboratory* Oak Ridge, Tennessee 37831 USA D. K. MANSFIELD, H. PARK and L. C. JOHNSON Princeton Universityt Princeton, New Jersey 08544 USA Abstract — The propagation of submillimeter-waves (smm) in tokamak plasmas has been investigated both theoretically and experimentally to ensure successful measurements of electron density and plasma current distributions in tokamak devices. Theoretical analyses have been carried out to study the polarization of the smm waves in TFTR and ISX-B tokamaks. A multichord smm wave interferometer/polarimeter system has been employed to simultaneously measure the line electron density and poloidal field-induced Faraday rotation in the ISX-B tokamak. The experimental study on TFTR is under way. Computer codes have been developed and have been used to study the wave propagation and to reconstruct the distributions of plasma current and density from the measured data. The results are compared with other measurements. INTRODUCTION The measurement of the radial distribution of the toroidal plasma current is of fundamental importance in fusion research of tokamaks. A method for measurement of this parameter was proposed by DeMarco and Segre.1 Their analyses show that the distribution can be obtained indirectly by measurement of the poloidal magnetic field which can be determined by projecting linearly polarized smm laser beams through the plasma and measuring the Faraday rotation of the polarization. If the Voigt effect is negligible and the wave is initially linearly polarized parallel or perpendicular to the toroidal magnetic field, the wave will undergo simple Faraday rotation, 0v, which is proportional to the line integral of the electron density times the poloidal magnetic field along the chord. In the case where the Voigt effect is large, a wave equation must be solved for the polarization evolution on the Poincare sphere. Recently, Vuolo and Galvao2 derived the equation of propagation including collisional attenuation to first order. Gomez and Lax3 have also examined the Voigt effect on the measurements of plasma current distributions in the Alcator tokamak. Since the rotation of the polarization is dependent on the electron density and magnetic field, *This work was supported by the Division of Magnetic Fusion Energy, U.S. Department of Energy, under contract No. DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc. +Thi« work was sunnorted bv U.S DOF. contract No. DE-AC02-CHO-3073.
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