23P077-P
Stabilization Analysis of Neoclassical Tearing Mode in Fusion Plasmas
核融合プラズマにおける新古典ティアリングモードの安定化解析
Daiki Kurita, Kozo Yamazaki, Hideki Arimoto, Tetsutarou Oishi, Tatsuo Shoji
栗田大輝、山﨑耕造、有本英樹、大石鉄太郎、庄司多津男
Nagoya Univ., Furo-cho Chikusa-ku, Nagoya 464-8603, Japan
名大院工 〒464-8601 名古屋市千種区不老町
For stabilization of neoclassical tearing mode (NTM), Electron Cyclotron Current Drive (ECCD) is used.
The change of the EC control efficiency depends on EC injection width and the lag in the EC injection
phase from O-point of magnetic island. The time variation of magnetic island is described by themodified Rutherford equation. In this work, NTM by ECCD is analyzed using 1.5-dimensional transport
code TOTAL. NTM can be stabilized with less EC current when the lag in the EC injection phasefrom O-point of magnetic island is smaller and EC injection width is narrower.
1. Introduction
For the achievement of high beta value intokamak fusion reactors, it is important to control
magnetic islands produced by neoclassical tearing
mode (NTM) and to suppress plasma confinement
degradation [1]. For stabilization of NTM,
Electron Cyclotron Current Drive (ECCD) is used.
Figure1 shows the model of EC modulation inphase with island rotation. The stabilization
efficiency of the EC current localization changes
by EC injection phase, position and width.
However, how much the efficiency of the EC
current change by these values is not clarified.

described by the modified Rutherford equation[2].

dw=Γ∆’+ΓBS+ΓGGJ+Γpol+ΓEC
dt(1)

Where Γ∆’ is the classical stability index definedas the logarithmic jump of the radial magnetic
perturbation across the rational surface[3]. Theterms ΓBS, ΓGGJ, Γpol and ΓEC represent effects ofthe bootstrap current, the field line curvature[4],the ion polarization current[5] and EC current
drive.
3. Numerical result
The change of the EC control efficiency ηec bythe lag in the EC injection phase from O-point ofmagnetic island Δαc is shown in Fig.2, whrere ηec
is given as follows [6]d EC Fig.1 The model of EC modulation in phase with island d  2 cos( m ) jd d  2

rotation

1EC.

(2)

j EC
f=0.5
f=0.250.80.6ηec

2. Numerical modelIn this work, plasma parameter change due toNTM is analyzed and the NTM control by ECCD
was studied using 1.5-dimensional transport codeTOTAL. The anomalous transport model usedhere is GLF23 that can simulate H-mode plasma.
The plasma equilibrium is solved by the Apollocode. The time variation of magnetic island is0.40.2000.05 0.1 0.15 0.2 0.25
ΔαFig.2 EC current efficiency ηec to a function of EC
injection phase ΔαcFor the smaller lag in the EC injection phase , ηec
becomes larger value. In the case of f=0.5(halfof the magnetic island), ηec is about 0.7 whenΔαc is nearly equal to zero. On the other hand,for f=0.25(narrower EC injection width case), alarge value ηec =0.9 can be achieved. Therefore,
NTM can be stabilized with less EC current if
the lag in the EC injection phase is smaller andEC injection width is narrower.
Temporal evolution of magnetic island widthin ITER parameter (major radius: 6.2[m],minor radius: 2.0[m], plasma current: 15.0[MA],troidal field: 5.3[T]) is shown in Fig.3. ECcurrent is Iec=80[kA], and EC injection width is(a)f=0.5, or (b)f=0.25.
0.25(a)0.2

0.20

Δαc=0.25

0.15

W

0.15
0.1

0.05

0.10

0.00

0.05
00.25
(b)
0.2

Δαc=0.25
0.20

0.15

w

0.15
0.1

0.10
0.05

0.05
030

0.00
35

40
45time(s)50

Fig.3 Temporal evolution of magnetic island
width W for EC injection width (a)f=0.5 and(b)f=0.25

According to Fig.2, the EC control efficiency is ahigher value when the lag in the EC injection
phase from O-point of magnetic island is smallerand EC injection width is narrower. So NTM canbe stabilized when  c ≦0.10 and f=0.25.
The temporal evolution analysis of central
electron temperature and the stabilization
effect of non-resonant helical field application
will also be reported in the conference.

References[1] Y. Takahashi, K. Yamazaki et al., Journal of Physics:
Conference Series 123 (2008) 012036.
[2] N. Hayashi, A. Isayama et al., J. plasma Fusion Res.
80,605(2004)[3] H. P. Furth, P. H. Rutherford et al., Phys. Fluids, 16,1054(1973)[4] A. H. Glasser, J. M. Greene and J. L. Johnson, Phys.
Fluids, 18, 875(1975)[5] H. R. Wilson et al., Phys. Plasmas, 3, 248(1996)[6] Hegna C.C. and Callen J.D. Phys. Plasmas 42940(1997)