RECENT RESULTS OF TANDEM MIRROR EXPERIMENTS IN GAMMA 10 AND HIEI

摘要

Confinement of ICRH plasmas in the GAMMA 10 and HIEI tandem mirrors has been investigated. In GAMMA 10, ions are heated to several keV, and hot ion modes, T_i/T_e > (m_i/m_e)~(1/3), are produced. The ion pressure in the central cell increases approximately linearly both with the power radiated from the antennas and with the magnetic field. A record ion temperature of about 10 keV is obtained at the maximum magnetic field (～0.57 T). A mixture of deuterium and hydrogen plasmas is formed, and thermonuclear fusion neutrons are detected for the first time in a tandem mirror. In typical GAMMA 10 tandem mirror operations, strong radial electric fields are naturally produced, and density fluctuations are well suppressed. Confinement of the core plasma is consistent with the classical processes of axial potential confinement. In HIEI, ICRF waves are used for axial potential formation as well as for plasma production, heating and MHD stability. When one of the limiters is positively biased, H mode-like behaviour appears in the plasma, resulting in an improvement of the radial confinement by a factor of 2.5. With a combination of limiter biasing and axial potential formation by the resonant RF, a central cell beta higher than 10% has been achieved at a plasma density of ～1.0 × 10~(13) cm~(-3).