A tokamak, which is the most successful device now on the road to controlled fusion, has the major disadvantage of pulsed operation because of a need to induce a toroidal current in the plasma. The application of rf to drive the current in steady-state tokamak reactors has been considered by a number of authors. 1 " 5 A method of producing continuous current carried by electrons in the tail of distribution function via quasilinear Landau damping of high-phase-velocity rf waves near the lower hybrid (LH) frequency has been proposed. 4,5 The linear and quasilinear Landau damping of slow electrostatic waves near LH frequency has been confirmed in a linear test device 6 and in the LH electron heating experiment on the tokamak (Doublet IL4). 7 These experiments provide a physical base for understanding the quasilinear Landau damping in the toroidal plasma with a relatively high electron temperature. Recently, the current generated by the unidirectional electron plasma waves has been observed in linear devices 8 * 9 and a toroidal device. 10 These experiments have been carried out in a plasma with a lower electron temperature, in which a transfer of momentum from LH waves to electrons via collisional absorption is significant.In order to make effective coupling between the LH waves and electrons, it is necessary to avoid the deposition of the rf energy into ions resulting ^. Mandelbrot, Fractals: Form, Chance, and Dimension (Freeman, San Francisco, 1977). e from the linear mode conversion and the excitation of parametric instabilities. The previous experiments on the rf ion heating indicated that i-for w Q /w lh {$) ^ l c 6 the ions did not interact with i the rf waves and the parametric decay instabilities almost disappeared, 11,12 where ou 0 is the frequency of the applied rf field and oo lh (0) is the LH QS frequency at the center of the plasma column. In this Letter, we report the experimental study on s the coupling between the rf waves and electrons under the conditions of oo 0 /uo lh (0) < 2 and the relatively high electron temperature in a tokamak. J-The experiment, with a 750-MHz rf source, e 6 was performed in the J FT-2 (JAERI Fusion Torus) i tokamak, which was a conventional tokamak with a major radius of JR 0 = 90 cm and a minor radius of a = 25 cm. The experimental setup and the discharges were reported in detail, 13 and hence will be described only briefly here. In the present l-experiment, the following discharge was used as a magnetohydrodynamically stable operation; toroidal magnetic field B t = 14 kG, plasma current I p = 3Q kA, mean line-of-sight electron density n ^3xl0 12 cm -3 , central electron temperature T^ -(250 eV)/k and effective ionic charge Z e ff of 2-5. The working gas was deuterium. The wave-3 guide array employed here consists of four indei pendently driven waveguides mounted 1.5 cm 5 away from the plasma edge, which is defined by It is observed that the waves launched from a phased array antenna of four waveguides couple effectively with electrons under the condition of oo 0 /oo lh (...

The light scattering spectrum from a high temperature plasma is calculated for the second order in v/c (c=light speed) and the second order approximate formula is obtained from the calculation. The blue side shift of the peak derived from the second order approximate formula agrees well with that of the full relativistic spectrum for an electron temperature of several tens of kilo electron-volts and less. The second order apparent temperature and density are deduced with an accuracy of better than 8 percent in the range up to 20 keV and 100 keV for scattering angles θ=90° and 50°, respectively, by application of the least-square procedure.

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Results from the JFT−2a (DIVA) experiments made with a separatrix magnetic surface are described. The main conclusions are: (1) A separatrix magnetic surface is stably located inside the material surface. (2) A plasma enclosed in a separatrix magnetic surface is similar to that of a conventional tokamak as far as the magnetohydrodynamic properties are concerned. (3) Measured parameters of the main plasma column are consistent with those expected from a conventional tokamak. (4) The electron density and temperature in the scrape-off layer are about ten times less than the values at the center of the main plasma column. (5) Heat and particle fluxes to the divertor region are axisymmetric and several times less than those of the total loss fluxes from the main plasma column. (6) Runaway electrons are well guided to the divertor region.