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(EXP4/11) Quasi-Steady-State Operation around Operational Limit in HT-7

J. Li¹⁾, J. K. Xie¹⁾, B. N. Wan¹⁾, J. R. Luo¹⁾, X. Gao¹⁾, Y. Zhao¹⁾, Y. Yang¹⁾, G. L. Kuang¹⁾, Y. Bao¹⁾, B. J. Ding¹⁾, Y. X. Wan¹⁾, and HT-7 Team
 
¹⁾ Institute of Plasma Physics, Academia Sinica, China

Abstract.  Efforts have been made on HT-7 tokamak for extending the stable operation boundaries. Extensive RF boronization and siliconization have been used and wider operational Hugill diagram was obtained. Transit density reached 1.3 time of Greenwald density limit in ohmic discharges. Stationary high performance discharge with q_a = 2.1 has been obtained after siliconization. Confinement improvement was obtained due to the significant reduction of electron thermal diffusivity $\chi_{\mathrm{e}}^{}$ in the out region of the plasma. Improved confinement phase was also observed by LHCD under the density range 70% $\sim$ 120% of Greenwald density limit. The weak hollow current density profile was attribute to off-axis LHW power deposition. Code simulations and measurements showed a good agreement of off-axis LHW deposition. Supersonic molecular beam injection has been successfully used to get stable high-density operation in the range of Greeenwald density limit.

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