LHD における外部共鳴磁場印加による粒子輸送への影響

27pA10Effects of resonance magnetic perturbation field on particle transport in LHD
田中謙治 1, M. Jakubowski2, A. Dinklage2, 榊原悟 1, 成嶋吉朗 1, 居田克巳 1, T. Evans3 他
1

核融合研,2 マックスプランクプラズマ物理研究所

K. Tanaka1, M. Jakubowski2, A. Dinklage2, S. Sakakibara1, Y. Narushima1, K.Ida1, T. Evans3 et al.,1

NIFS, 2Max-Planck-Institut für Plasmaphysik, EURATOM Association, Greifswald (Germany),
3

General Atomics (U.S.A)

Resonant magnetic perturbation (RMP) coils are one of the mosteffective controlling tools to mitigate edge localized mode (ELM)
activity in tokamaks [1]. In addition to ELM mitigation, RMP
changes transport as well. For example, in DIII-D, enhancement ofparticle transport, the so-called particle pump-out, is reported [1].
Understanding the effect of RMPs on transport is essential for theELM mitigated operation in tokamaks. In contrast to tokamaks, 3D
devices allow for detailed assessments of the effect of stochastic
fields on transport. In LHD, ELM-like events are observed in H-modes at relatively high plasma beta [2]. ELMs are, however, notregarded as a critical issue for LHD, since ELMs are not observed inmost of the L mode discharges and in other improved modes such as
high ion temperature discharges [3]. But the effect of RMPs on
transport can also be used as a tool to control transport. The
advantage of LHD is that the magnetic field structure in ergodic
region is well determined and agrees with field calculations
confirmed by saddle loop coil measurements. The experiments aredone at the outwardly shifted configuration with a magnetic axis
Fig.1 Comparison of (a) line averaged
density, (b) line integrated fluctuation
position at 3.9m and the width of ergodic layer becomes order of 30%
and (c) central electron temperature withof plasma minor radius. Figure 1 shows comparison of time trace withand without RMP
RMP and without RMP. The RMP forms an m/n=1/1 magnetic islandclose to the last closed flux surface. The power ofthe NBI has been reduced from 5.5 to 2.2 MW at
t=5.3sec. The density is modulated at 5Hz by
external gas fueling to estimate diffusion coefficient(D) and convection velocity (V). In low density,
high power phase (t=3.1-5.3), edge D at ρ>0.7 is
0.67+-0.015m2/s and 0.55+-0.014m2/sec with andwithout RMP respectively, while V is almost
identical. This indicates RMP causes enhanced
Fig.2 (a) Te, (2) ne and (c) fluctuation amplitude profile in
the high density phaseedge diffusion. In high density, low power phase
after t=5.3s, a higher increase of density is observedwith lower external fueling without RMP. As shown in Fig.1(a), after t=5.3 sec, the density perturbation becomes verysmall in the case without RMP. Moreover, the figure indicates the density to be much better controlled with RMPs. Thisis sought to be due to the enhanced particle transport with RMPs. Figure 2 shows comparison of profiles of Te, ne, anddensity fluctuation amplitude with and without RMP at low power (high density). With RMPs, a flattening of Te and ne isseen at ρ=0.95-1.1 at the position of the m/n=1/1 island (cf. Fig. 2(a) and (b)). It is noted that this flattening does notoccur in preceding phases of the discharge at low density, high power phase (t=3.1-5.3s). Fluctuation amplitudes
measured by two dimensional phase contrast imaging (2D-PCI) [4] indicate the peak of fluctuation at ρ=0.8 without
RMPs in inner regions with flat density profile. With RMPs, the fluctuation peaks around m/n=1/1 island. Concluding,these observations indicate that RMPs affect the turbulence character and enhance the particle transport in the discharges
investigated. [1] T. Evans et al., Nature Physics, 2,(2006), 419,[2] K. Toi et al., proceeding of 23rd FEC 2010, October 11-16 (2010)
Daejon, Korea,[3] K. Ida et al., Physics of Plasmas 16, (2009), 056111,[4] K. Tanaka et al., Rev. Sci. Instrum. 79, (2008), 10E702