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(EX/C4-3) Increased Understanding of Neoclassical Internal Transport Barrier on CHS

T. Minami¹⁾, A. Fujisawa¹⁾, H. Iguchi¹⁾, Y. Liang¹⁾, K. Ida¹⁾, S. Nishimura¹⁾, M. Yokoyama¹⁾, S. Murakami¹⁾, Y. Yoshimura¹⁾, M. Isobe¹⁾, C. Suzuki¹⁾, I. Nomura¹⁾, K. Toi¹⁾, M. Yoshinuma¹⁾, A. Shimizu¹⁾, C. Takahashi¹⁾, K. Matsuoka¹⁾, S. Okamura^1)
 
1) National Institute for Fusion Science, Toki, Japan

Abstract.  The recent progress of the study on neoclassical internal transport barrier (N-ITB) of Compact Helical System (CHS) is reported. This barrier is formed due to the positive electric field and the electric field shear that are created by bifurcation of radial electric field with the electron cyclotron (EC) heating on helical devices. Previously N-ITB was observed for ECH plasma, recently N-ITB barrier was also observed for EC (53.2 GHz 2nd harmonic) heated NBI plasma. The N-ITB of EC heated NBI plasma is formed at the outer location ( r/a = 0.4 - 0.6) in comparison with that ( r/a = 0.3) of ECH plasma, so that the improved confinement region is expanded. The improvement in the ion energy transport is also observed and the ion temperature is increased up to 400 eV along with the electron temperature, that is two times higher than that of the plasma without N-ITB. The particle transport is studied by measuring the peak energy of Titanium K$\alpha$ line intensity with the soft X-ray CCD camera. The energy is shifted from 4.68 kV to 4.73 kV by forming N-ITB. The improvement of the impurity transport has been confirmed inside N-ITB by comparing the experimental result with the MIST code.

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