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(THP2/21) Analysis of Plasma Current Profile Driven by Coaxial Helicity Injection in Tokamak

Cheng Zhang¹⁾, Deng Zhou¹⁾,Sizheng Zhu^1)
 
1) Institute of Plasma Physics, Chinese Academy of Sciences, China

Abstract.  The plasma current profile driven by coaxial direct current helicity injection in a low-aspect-ratio toroidal configuration is investigated by applying the principle of minimum energy dissipation rate. It is shown that the current profile modes are mainly decided by Langrange multiplier $\beta$. Some critical values of $\beta_{\mathrm{c}}^{}$ are found. Different current profiles are obtained in different $\beta$ ranges. Three typical current profiles are presented. The key features agree well with experiment as the first case of $\beta$ < 7. Large driven plasma current and a typical current profile in a normal tokamak can be obtained in the region of $\beta$ = 7 to 9.65. There exist reversions of both j_$\varphi$ and B_$\varphi$ in the central part when $\beta$ becomes higher than $\beta_{\mathrm{c}}^{}$ $\approx$ 9.65. For a selected geometry the values of $\beta_{\mathrm{c}}^{}$ weakly depend on other parameters. There exist critical values of plasma temperature and bias voltage to induce the transformation of current profile mode. The profile of $\lambda$ = $\mu_{0}^{}$j_$\varphi$/B_$\varphi$ is non-uniform in the plasma and a larger deviation from force free states appears when $\beta$ becomes higher.

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