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A diagnostic system has been developed to measure the direction of the local magnetic field within the plasma of a tokamak by making use of Zeeman splitting in an injected neutral lithium beam. A linearly polarized dye laser is used to pump the π component of the 2S-2P resonant transition. The laser polarization is rotated at a fixed frequency, and phase analysis of the subsequent fluorescence identifies the local field direction. The instrument can monitor many radial points within the plasma simultaneously, allowing a current density profile to be determined on a single shot basis.

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In the Doublet III tokamak a variety of cross-sectionally-shaped plasmas has been investigated. Simple magnetically-shielded ionization gauges monitoring the working gas pressure show a striking dependence upon plasma shape. Average neutral density varies over two orders of magnitude. In the exteme cases of the simplified poloidal divertor shapes, the pressure exceeds 10−3 Torr.

No abstract