Experiments of Plasma Confinement in JIPP Stellarator-I : Preliminary Results Using J×B Gun and ECRH Plasma

概要

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To investigate the dependence of plasma confinement on the properties of the magnetic field (rotational transform angle, shear, magnetic well, plasma radius etc.), a circular ℓ=3 stellarator with a vertical field is constructed with taking care of the accuracy. Several kinds of plasma sources (J×B type gun with a fast acting valve, titanium gun, ECRH, r. f. stochastic heating and ohmic heating by air coil) are prepared. In this report, preliminary results of the experiments on the plasma confinement using J×B type gun and ECRH plasma are described. The diffusion coefficient estimated from the decays times and the plasma radius are inversely proportional to the square of the rotational transform angle ı. The profile of the density distribution is similar to (r/a_s)^<2J>_<-2/3>[1.25(r/a_s)^3] which corresponds to the relation D ∝ ı^<-2> ∝ r^<-4>. The diffusion coefficients estimated from the Bessel distribution are down to 1/7 ~ 1/17 times of the Bohm one. If the foregoing distribution is adoped, the ratios become to 1/17 ~ 1/40. The confinement time does not depend appreciably on the property of the magnetic well (and antiwell). The dependence of the confinement time on the magnitude of the magnetic field is appearently linear. As the ion temperature of the plasma of J×B type gun depends on the magnitude also, the scaling law is not determined yet and more detailed investigation are being carried out.
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