F. Shimpo

R. Kumazawa

S. Masuda

T. Ido

T. Mutoh

T. Seki

T. Watari

National Institute for Fusion Science (NIFS-Repository)

§ 19. Electron Heating near the Plasma Center with 130 MHz Fast Waves ldo, T. (Dept. Energy Eng. & Sci., Nagoya Univ.) Seki, T., Watari, T., Kumazawa, R., Mutoh, T., Shimpo, F., Masuda, S. (Grad. Univ. Advanced Studies) Noninductive current drive is required for steady state operation of tokamak devices. Fast wave current drive is proposed as a promising method which can be applied theoretically even to the high density and high temperature plasmas such as a reactor plasma. In the JIPP T-IIU tokamak the new type antenna for the fast wave current drive experiment was in-stalled1),2) and the experiment has been conducted. To drive the plasma current noninductively by the waves, the electrons must obtain the momen-tum through the interaction with the waves so that they are accelerated in a toroidal direction. Thus first of all it is important to judge whether the electrons interact with the waves or not. The elec-tron cyclotron emission (ECE) signal is sensitive to the electron temperature. From the ECE signals we can recognize the variation in the electron temper-ature caused by the interaction between the elec-trons and the waves. Figure 1 displays the time evolution of the ECE signals in a typical shot. The plasma current is 220 kA. The toroidal magnetic field is 3 T. The experi-ment was performed in the deuterium gas. Though there is the 6th harmonic ion cyclotron resonance layer of the deuterium at the plasma center, it is confirmed theoretically and experimentally that the waves are hardly absorbed at such a higher har-monic resonance layer3). The radio frequency (RF) power radiated from antenna is about 100 kW. The ECE signals in Fig. 1 rise when RF power is applied to the plasma. While the electron tem-perature near the plasma center rises immediately at the turning on the RF power, the temperature near the edge does not rise. This indicates that the fast wave is directly absorbed by the electrons near the plasma center. The electron temperature profile is peaked at the plasma center with the injection of the 186 fast wave. The ECE signals decrease gradually after RF power is turned on because the density in-creases during the injection of RF power (Fig. 2 ). At present we can't increase the RF input power because of the disruption induced by the increase of the impurity ions (Fig. 3). In JIPP T-IIU boronization will be carried out and it is expected to reduce the impurities. ]1.5._____. ! ] 1 .~ (I) ~ 0.5 t---~./. ~ ~~~--~~--~~ 150 200 250 time(msec) Fig. 1. The time evolution of the ECE signals.The position of plasma center is 0.93 m. The po-sition of each chord is indicated in the figure. Fig. 2. The time evolution of the line averaged density 1.2 ~...,...............,.~.,-r-o._,..,., ............. "TTT".......-ro"WT"T"~,..,..., - 1 ·a ::s 0.8 t '-" 0.6 l 0.4 .s 0.2 Fig. 3. The line emission of the impurities Reference 1)Seki, T., et al. : Ann. Rep. NIFS (1993-1994) 166 2)Seki, T ., et al. : Ann. Rep. NIFS (1994-1995) (to be published) 3)Seki, T., et al. : Nucl. Fusion .11. (1991) 1369 

Electron Heating near the Plasma Center with 130 MHz Fast Waves

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