A. Sagara

D.A. Rasmussen

D.J. Hoffman

F. Shimpo

Group CHS

K. Nishimura

R. Kumazawa

S. Masuda

T. Mutoh

T. Seki

T. Watari

Y. Hasegawa

National Institute for Fusion Science (NIFS-Repository)

§6. ICRF Heating Plasma Qualities for Various Boronized Wall Conditions Kumazawa, R., Nishimura, K., Sagara, A., Hasegawa, Y. (Nagoya Univ.) Masuda, S. (Grad. Univ. for Advanced Studies) Mutoh, T., Shimpo, F., Seki, T., Watari, T., Rasmussen, D.A., Hoffman, D.J. (Oak Ridge National Laboratory) CHS Group We describe how different plasma qualities were for two different boronized vacuum wall conditions in this section. We tried two boronization schemes; referred to boronization with small flow rate and with large flow rate. In the boronization with small flow rate, boron gas was fed into He glow discharge( 1 Ax200V with one electrode) at 30 to 40mtorr using 1501/sec vacuum pump(effective pumping speed is estimated about 101/sec). Unfortunately we did not measure boron gas flow rate, however, the oven temperature of vaporized boron could tell us its pressure. The operating oven temperature ranged 70°C, where the boron vapor pressure was 4.5torr. On the other hand, 15001/sec vacuum pump was used at effective pumping speed, about 7001/sec in the boronization with large flow rate. The pressure in He glow discharge was 6 to 20mtorr. The He gas flow was much larger so that He glow discharge power was tripled by adding 2 new electrodes. The operating oven temperature was 70°C same as in the boronization with small flow rate. In Fig.1, various plasma parameters were compared such as stored energy, radiated power and ratio of average electron density to plasma production rate deduced from Ha!Da measurement, indicating relative particle confinement time from top to bottom. Solid and dashed lines showed the boronization with small flow rate and with large flow rare, respectively. In these experiments, gas puffing rate, injected RF power and average electron density were same, ranging in 20-17torrl/sec, 500-600kW and 1-4.5x1013cm-3, respectively. The particle confinement time was also same during whole ICRF heating period as shown in Fig.1, where Ha/Da intensities were measured at 8 different toroidal sections. The obtained stored plasma energies, however, were different; the stored energy in solid line reached to 2kJ and lasted at the end of RF pulse. On the other hand, the stored plasma energy started to decrease with increase in the radiated power at the middle of RF pulse and disappear at the end of RF pulse. with radiated power of 300kW in dashed line. We could not find any other differences except for toroidal distributions of Ha!Da. Figure 2 shows its toroidal distribution at 80ms. The deuterium gas was fed at No.2 port and 5 antenna were sited at 1, 3, 5, 7 for P-port antenna and at 8 for U -port antenna. The toroidal uniformity of Ha!Da in solid line was much . better than in dashed line, which tendency was observed during whole ICRF heating pulse. This experimental result suggests that uniform gas puffing will provide a successful future ICRF heating on LHD. 2.5 2.0 2 1.5 C'::S :.a 1.0 ~ 50 100 150 time [msec] 400~------~------~~-----. o~~~~~------~--~--~ 0 50 100 150 time [msec] 800x1 o-6 ~-------r---------,-----------, 50 100 150 time [msec] Fig.l Time evolution of various plasma parameters in boronization with small gas flow rate (solid lines) and with large gas flow rate( dashed lines). 400 350 ......... 300 ~ 250 ~ 200 1::5 :r: 150 100 50 No.1 No.5 Fig.2·Toroidal distribution of HaiDa in boroniza-tion with small gas flow rate (solid lines) and with large gas flow rate( dashed lines). 203 

ICRF Heating Plasma Qualities for Various Boronized Wall Conditions

ICRF Heating Plasma Qualities for Various Boronized Wall Conditions

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)