A. Ejiri

Group. .CHS

K. Kawahata

K. Tanaka

S. Okajima

National Institute for Fusion Science (NIFS-Repository)

§25. Comparison of Electron Density Decay between Different Magnetic Axis Positions in CHS Tanaka, K., Ejiri, A., Kawahata, K., .CHS Group Okajima, S. (Chubu Univ.) Temporal evolutions of electron density profiles are measured by an HCN laser interferometer[ I], and compared between the two different cases of magnetic axis position of NBI heated plasma. One is at Rax=92.lcm and the other is at Rax=97.4cm. Rax is the position of the vacuum magnetic axis on the equatorial plane. In the former case, the inboard side of the plasma is attached to the inner wall of the vacuum vessel and, in the latter case, the outboard side of the plasma is attached to the ICRF antenna. In this series of experiments, the ICRF antenna cuts the plasma edge and the plasma minor radius is reduced by about 10% at Rax=97.4cm. Figure 1 (a) and (b) show the temporal evolutions of line density before and after turning off of the gas puffing in the two cases. In Figs. 1 , Z indicates the position of the interferometer chords measured from the equatorial plane. The last closed flux surface is 14.6cm at Rax=92.1cm, and is 14.3cm at Rax=97.4cm. At Rax=97.4cm, the line density at Z=l3.6cm is almost zero. This indicates the ICRF antenna cuts the plasma like a limiter. Figure 2( a) and (b) show the Abel inverted density profiles just before and 25msec after turning off of the gas puffmg. The density profiles at Rax=92.1 em are clearly broader than those at Rax=97 .4 em. This is different from the previous results. Before installation of the ICRF antenna, the density profiles at Rax=92.1cm are more peaked than those at Rax=97.4cm[2]. The decay time, which is defined as (1/ne dnJdtt 1, of volume averaged density <ne> and central density ne(O) are calculated from Figs.2. At Rax=92.lcm, the decay time of <ne> is 120msec and the decay time of ne(O) is 530msec. At Rax=97.4cm, both decay times of <ne> and ne(O) are 90msec. The decay time of ne(O) at Rax=92.1cm is much longer than that at Rax=97 .4cm, although the decay time 222 of <ne> does not differ much each other in the two cases. These suggest the difference of particle transport between two cases exists especial! y in the central region of plasma 3. s;::::;:::;:::;:;:::;:::;::::;::;:;:::;:~,_,_I"""T""'--r"T-r"T""T""T""~ ~3. ~ 2.st_. _________ "" ,-X ~2·~--------------·~ 1. Q) Q 1.u-.---------....._ Q) :J 0. 110 Gas Puff 12q 130 t\msec) 120 .130 140 t(msec) 140 150 150 160 Fig. 1. Temporal evolutions of line density (a) at Rax=92.1cm and (b) at Rax=97.4cm. Ot.&...L..L..I..I..~..I..L..&.~~~Oc:....... ......... __._ ......... ....._.-.......--0 0.2 0.4 0.6 0.8 1 0 r/a 0.2 0.4 0.6. 0.8 1 r/a Fig. 2 Decay of electron density profiles after turning off of the gas puffing (a) at Rax=92.1cm and (b) at Rax=97 .4cm. References l)Tanaka,K., et al., Proc.21st EPS Conf. on Controlled Fusion and Plasma Phys., Montpellier, 18B Part 1 (1994)423 2)Iguchi,H., et al., Plasma Phys. Control. Fusion 36 (1994) 1091 

Comparison of Electron Density Decay between Different Magnetic Axis Positions in CHS

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)