Mirror end loss can be suppressed by applying an rf field at the mirror throat through low impedance coils. This method is verified to be effective for a high density plasma up to 1014 cm−3. Experimental results show that the rf field strength required for the plugging is dependent on the plasma density. The dependence differs according to the geometry of the coil. The mechanism of giving the density dependence is theoretically clarified for each coil. Particularly, it is shown that the electric field induced in the direction of the static magnetic field is intrinsic for the result of type-III coil where its efficiency for rf plugging is insensitive to the plasma density.
A method of plasma production by ion cyclotron wave heating has been developed in RFC-XX. Nagoya Type-Ill antennas were used for wave excitation, and gas was supplied through a gas box. The effect of the rotating field excitation on plasma production and heating was investigated. In the m = -1 rotational mode (rotation in the direction of ion cyclotron motion), the plasma density profile is flat within the gas box bore with a line integrated density n£ = 3 X 10 13 cm~2, and the ion temperature is T ; « 150 eV. For the m = +1 mode, a high density plasma was obtained with a different profile having a peak at the centre. In this mode, the line integrated density is n2 = 3 X 10 l4 cm~2, with the peak density n(0) = 7 X 10 13 cm" 3 .
Experimental data for ion cyclotron resonance heating in the RFC-XX machine in IPP-Nagoya are presented. The achieved ion temperature is as high as 100 eV at n = 1013 cm−3 and 1 keV at n = 1012 cm−3. The ion energy confinement becomes worse by the application of a longer pulse, which is found to be due to the enhanced charge-exchange loss and/or electron drag. Axially and azimuthally arrayed antennas are used in the heating, and the importance of the phasing is demonstrated. A simple model of the multiple-antenna problem is also given and used to interpret the experimental data.
In a circular cross-section plasma bounded by a limiter, the //-mode transition is triggered by a rapid rampdown in plasma current during auxiliary heating, even in the case when the edge electron temperature gradually decreases prior to the transition. This result suggests that the transition is governed by the enhancement of the magnetic shear near the plasma edge, associated with the radial modification of the edge current-density profile.PACS numbers: 52.55.Fa, 52.55.Pi
An experiment in a new regime of ion Bernstein wave (IBW) heating was carried out using 130 MHz high power transmitters in the JIPP T-IIU tokamak. The heating regime utilized the IBW branch between the 3rd and 4th harmonics of the hydrogen ion cyclotron frequencies. This harmonic number is the highest one used in IBW experiments conducted previously. The net radiofrequency (RF) power injected into the plasma is around 400 kW and is limited by the transmitter output power. Core heating of ions and electrons was confirmed in the experiment and density profile peaking was found to be a special feature of IBW heating. Peaking of the density profile was also found when IBWs were injected into neutral beam heated discharges. An analysis, using a transport code with these experimental data, indicates that particle and energy confinement should be improved in the plasma core region upon application of IBW heating. It is also found that the ion energy distribution function observed during IBW heating has a smaller high energy tail than those observed in conventional fast magnetosonic wave ICRF heating regimes. The ion energy distribution function obtained during IBW heating is in reasonable agreement with that calculated using the quasi-linear RF diffusion/Fokker-Planck model
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