D. Oikawa

J. Miyazawa

M. Takagi

M. Tokitani

N. "Ohno

R." Maekawa

S. Kajita

S. Masuzaki

National Institute for Fusion Science (NIFS-Repository)

Direct Power Generation by High HeatFlux Divertor PlasmasOhno, N., Oikawa, D., Kajita, S., Takagi, M.(Nagoya Univ.)Masuzaki, S., Miyazawa, J., Tokitani, M., Maekawa, R.In fusion devices, a divertor plate receives huge heatload released from a core plasma. If the huge heat loadcan be converted to electricity by using a thermionic en-ergy converter (TEC), the eﬃciency of the fusion reactorcould be improved. TEC has been developed for a longtime for application to nuclear thermionic power gen-erator in spacecrafts and combustion heated thermionicpower system. This is because TEC has good propertiessuch as high conversion eﬃciency and simple conﬁgura-tion.We have investigated basic property of TEC by 2DPIC simulation (Berkeley code). The emitter and thecollector are assumed to be made of tungsten with a workfunction of 4.5 eV and thoriated tungsten with a workfunction of 2.6 eV respectively. Figure 1 shows depen-dence of output current normalized by thermoelectronemission current from the emitter on distance d betweenthe emitter and the collector at an emitter temperatureof 2300 K. As decreasing d, the output current increasesexponentially to be unity at d = 0.1 mm. This meansthat virtual cathode formed in front of the emitter disap-pears at d below 0.1 mm, and all electrons emitted fromthe emitter can reach the collector.Based on the simulation result, we made a TECtest module having thoriated tungsten electrodes withd = 0.06 mm by using thin BN ﬁlm as an insulator.We performed veriﬁcation experiments of the TEC un-der a huge heat ﬂux by using Active cooling Test device(ACT) in NIFS as shown in Fig. 2. The emitter is heatedby an electron gun (its power is about 500 W) and theemitter temperature is gradually increased to be up to2000 K. The emitter temperature was measured with aradiation thermometer. Figure 3 shows the current den-sity J as a function of the emitter temperature. Theexperimental result agrees well with the PIC simulationresult. In high temperature region, the output currentdoes not saturate, probably because the initial velocity ofthe thermionic electron increases with the emitter tem-perature . In this experiment, TEC system eﬀectivelygenerated an electric power of 10 kW/m2 at 2000 K.The conversion eﬃciency from heat to electricity was es-timated to be 0.01.1) D. Oikawa, N. Ohno, S. Kajita, M. Takagi,S. Masuzaki, M. Tokitani and K. Asano, ICFRM-14,Aomori, Japan.Fig. 1: Simulation result of the output current as afunction of distance between electrodes.Fig. 2: Schematic of experimental setup.Fig. 3: Current density as a function of emitter temper-ature. Closed circles and diamonds represent the PICsimulation results. Experimental result is shown as asolid line.106§6. ire  Power Generation by High Heat Flux Divertor PlasmasOhno, N., Oikawa, D., Kajita, S., Takagi, M. (Nagoya Univ.),  Masuzaki, S., Miyazawa, J., Tokitani, M., Maekawa, R.

Direct Power Generation by High Heat Flux Divertor Plasmas

Direct Power Generation by High Heat Flux Divertor Plasmas

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