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(EX/P3-22) Experimental Evidence for Improved Confinement with Quasisymmetry in HSX

S.P. Gerhardt¹⁾, A. Abdou¹⁾, A. Almagri¹⁾, D.T. Anderson¹⁾, F.S.B. Anderson¹⁾, D. Brower²⁾, J. Canik¹⁾, C. Deng²⁾, W. Guttenfelder¹⁾, K. Likin¹⁾, S. Oh¹⁾, J. Tabora¹⁾, V. Sakaguchi¹⁾, J. Schmitt¹⁾, J.N. Talmadge¹⁾, K. Zhai^1)
 
1) University of Wisconsin-Madison, Madison, USA
²⁾ Electrical Engineering Department, University of California, Los Angeles, USA

Abstract.  Plasmas produced by second harmonic electron cyclotron heating (ECH) in the HSX stellarator provide the first evidence of transport improvement due to quasisymmetry in a stellarator. Comparisons are made between plasmas in the base quasihelically symmetric (QHS) configuration and two neoclassically degraded configurations which lack quasisymmetry (Mirror configurations). It is found that the plasma breakdown occurs more easily in the QHS configuration, indicating improved confinement of the breakdown electrons. The stored energy in the QHS configuration is up to six times larger than discharges in the Mirror configurations, and evidence is shown for enhanced prompt loss of trapped particles when the Mirror field is applied. The momentum damping rate is measured to be factors of three to four less in the QHS configuration than the Mirror configuration.

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