PLASMA MEASUREMENT BY FEEDBACK-STABILIZED DUAL-BEAM LASER INTERFEROMETER

概要

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The plasma density in a dynamic magneto arcjet is measured by a stabilized dual-beam laser interferometer proposed by the authors. The fringe shift for a 0.63μm beam of He-Ne laser is used to stabilize the interferometer against the effect of mechanical vibration by means of a feedback controlled speaker coil, while the other beam of 3.39μm, for which the effect of mechanical vibrations is excluded, is used to measure plasma density. Stability of ∿ 1/500 of one fringe for 0.63μm is obtained during a long period for frequencies lower than a few Hertz. Stability for higher frequencies, which determines the accuracy of the present measurement, is limited to ∿ 1/30 of one fringe for 0.63μm, which corresponds to ∿ 1/200 of one fringe and a line electron density of ∿ 1.5×10^<14>cm^<-2> for 3.39μm, by acoustic noise picked up by the speaker coil. The advantage of this technique over the single=laser technique is that the frequency response of the interferometer extends down to zero frequency. Since the effect of the neutral gas background is practically reduced to zero, the present interferometer is to be applied advantageously to the diagnostics of the plasma produced in high pressure gases.
核融合科学研究所の論文