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(EXP1/02) First Results from Operation of the H-1NF Heliac at Increased Magnetic Field and Power

J. H. Harris¹⁾, B. D. Blackwell¹⁾, J. Howard¹⁾, M. G. Shats¹⁾, C. Charles¹⁾, S. M. Collis¹⁾, F. J. Glass¹⁾, A. Gough¹⁾, C. A. Michael¹⁾, H. Punzmann¹⁾, W. M. Solomon¹⁾, G. B. Warr¹⁾, G. G. Borg^1)
 
1) Australian National University, Canberra, Australia

Abstract.  The H-1 heliac is being developed as a national research facility. A new power supply system which allows operation to fields $\leq$ 1 T has been commissioned; the ripple in the supply is controlled to < 0.01% to eliminate induced currents. Up to 100 kW of rf power at 7 MHz is used at present to produce plasmas using helicon waves. Multiple diagnostic studies of these plasmas and comparison experiments with a linear helicon device suggest that the near fields of the rf antennas result in ion temperatures that increase at the edge of the plasma, even though the antennas are 3-4 cm outside the last closed flux surface. Probe and spectroscopic results indicate that there the mass flow velocities are much less than the ExB velocity. Thus, radial force balance holds in detail, and the ambipolar radial electric field balances the ion pressure gradient. In L-mode plasmas, tomographic interferometry and probe studies show low-mode-number coherent oscillations in electron density and electron and ion temperatures that are suppressed at the L-H transition.

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