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(EXP1/09) Internal Transport Barrier and $\beta$ Limit in Ohmically Heated Plasma in TUMAN-3M

   
M. V. Andreiko , L. G. Askinazi , V. E. Golant , N. A. Zhubr , V. A. Kornev , S. V. Krikunov , S. V. Lebedev , L. S. Levin , G. T. Razdobarin , V. V. Rozhdestvensky , V. A. Rozhansky ¹ , A. I. Smirnov , M. Tendler ² , A. S. Tukachinsky , S. P. Yaroshevich 
 
Ioffe Physico-Technical Institute, Russian Academy of Sciences, St.Petersburg, RUSSIA
¹ St.Petersburg State Technical University, St.Petersburg, RUSSIA
² Alfven Lab., EURATOM-NFR Assoc., Royal Institute of Technology, Stockholm, SWEDEN

Abstract
An Internal Transport Barrier (ITB) was found in ohmically heated plasma in TUMAN-3M  (R$_0$ = 53 cm, a$_l$ = 22 cm - circular limiter  configuration, $B_t \leq 0.7 T, I_p \leq 175$ kA, $<n> \leq 6.0\cdot 10^{19} m^{-3}$). The barrier reveals itself as a formation of a steep gradient on electron temperature and density radial profiles. The regions with reduced diffusion and electron thermal diffusivity are in between r = 0.5a and r = 0.7a. The ITB appears more frequently in the shots with higher plasma current. At lower currents ($I_p < 120$ kA) the ITB is rare. In the ohmic H-mode  with ITB the thermal energy confinement  is in the range of 9-18 ms. The enhancement factor over ITER93-H(ELM-free) scaling is up to 2. The results of experimental study of $\beta_N$ limit in the ohmically heated plasma are presented. Stored energy was measured using diamagnetic loops and compared with W calculated from kinetic data obtained by Thomson scattering and microwave interferometry. Measurements of the stored energy and of the $\beta$ were performed in the ohmic H-mode before and after boronization  and in the scenario with the fast Current Ramp-Down in the ohmic H-mode. Maximum value of $\beta_T$ of 2.0 % and $\beta_N$ of 2 were achieved. The $\beta_N$ limit achieved is ``soft'' (nondisruptive) limit. The stored energy slowly decays after the Current Ramp-Down. No correlation was found between beta restriction and MHD phenomena.

     

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