Development of Magnetic Field Distribution Measurement in a Plasma by Means of Beam Probe/Laser Spectroscopy

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A technique of improving the accuracy of magnetic field distribution measurement in a plasma utilizing the Zeeman effect with a combination of the particle beam injection and laser induced fluorescence method was investigated. It is, however, concluded that the intensity of laser-induced fluorescence is not enough to achieve good time-and space-resolution. Then, we have shifted our effort to the improvement of the accuracy of those which utilize the Motional Stark Effect (MSE). A code has been developed to simulate the MSE spectrum of H_<alpha>, taking accurately and precisely into account the related atomic processes as well as geometries of the beam injection and observation line of sight. A beam attenuation by ionization and charge exchange in the plasma and an electron density dependence of the excitation are regarded. Configuration of the ion beam source, divergence of the beam, magnetic configuration of the tokamak, sustaining angle of the observation, and a slit function of the … More spectrometer are also taken into account.The results obtained from the simulation code are as follows :As for the optimum design of MSE diagnostics, 1) an ellipse of aspect ratio 2 is optimum for the ion source configuration, and 2) the diagnostic beam should be tilted by 25 degrees from the perpendicular direction, and should be observed from a port located at the toroidal angle of 70 degrees apart from the beam.As applications of the MSE spectral calculation, it has been shown that 1) it will be possible to obtain the electron density from the MSE spectrum, 2) poloidal magnetic field in a plasma can be determined from a simultaneous measurement with 4 linear polarizers having the polarization direction of 0,45,90, and 135 degrees with respect to the horizontal direction, and 3) utilizing the fact that the spectrum shows an asymmetry between red-shifted pi line and blue-shifted one due to the finite divergence of the beam, a divergence angle of 1.3 deg.of the heating neutral beam on the JFT-2M tokamak at JAERI was determined Less