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(EXP3/13) Comparative Study of CT Equilibrium and Stability Using Controlled Current Drive: Compact RFP, Spheromak and ST in a Single Device

Y. Ueda¹⁾, Y. Ono¹⁾, M. Tsuruda¹⁾, Y. Murata¹⁾, G. Yamada¹⁾, H. Hayashiya¹⁾, T. Itagaki¹⁾, M. Katsurai^1)
 
1) Department of Electrical Engineering, University of Tokyo, Tokyo, Japan

Abstract.  A comparative experiment of low-aspect ratio ( A $\approx$ 1.5) torus plasmas: compact RFPs, spheromaks and STs has been performed in the TS-3 and 4 CT devices. Especially, a compact RFP with q₀ as large as 0.3 was found to have low-n dynamo mode n = 3 like n = 2 mode of spheromak with q₀ $\approx$ 0.5. Under OH current sustainment, magnetic fluctuation and loop voltage were observed to increase inversely with its q-value. A new edge-current-drive method was developed by use of axial CT merging, realizing a balanced current drive together with the OH current drive. The balanced current drive was found to reduce the dynamo fluctuations of compact RFP and spheromak by factor 3. The multiple CT merging can be a promising edge-current drive because of its intermittent current drive and its detailed control of current profiles using varied size of colliding CTs.

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