23P095-P
Propagation and Absorption Properties of ICRF Wavein Finite Beta Plasma of LHD
LHD型ヘリカルプラズマにおけるICRF共鳴帯の伝搬・吸収特性
R. Seki1), K. Saito1), T. Seki1), A. Fukuyama2), K.Y. Watanabe1) and T. Muto1)
關 良輔1), 斎藤 健二1), 関 哲夫1), 福山 淳2), 渡邊 清政1), 武藤 敬1)
1) National Institute for Fusion Science, Toki 509-5292, Japan
2) Graduate School of Engineering Kyoto University, Kyoto 606-8501, Japan1) 核融合科研, 2)京大院工We analyzed the propagation and the absorption property of the ICRF wave in theplasma consisting of the helium as a majority ion and the hydrogen as a minority ion byusing the cold plasma approximation. As a result, the minority ratio with the maximum
absorption power is about 30% and the maximum absorption power rarely changes bychanging the density

1. Introduction
The heliotron type device such as theLarge Helical Device (LHD) is suitable for thesteady operation because the poloidal magnetic
field, which is required for the plasma
confinement, is made by the helical coil. Withthe Ion Cyclotron Range of Frequencies (ICRF)
and Electron Cyclotron Heating (ECH) the lowdensity discharges with 1x1019 m-3 are done formore than 3000 second in the LHD. In thehelical plasma, the plasma confinement
performance makes improvements with theincrease in the density. On the other hand,when the density increase and is more thandensity limit, plasma confinement performance
become very low, and the discharge stops due tothe density collapse. Therefore, it is necessary
to systematically investigate the heating
property of the ICRF and the ECH in therelatively high density for the long discharge
with the high confinement performance. In thisstudy, we investigate the propagation and theabsorption property of the ICRF wave in theLHD plasma with the relatively high density.
2. Analyses of ICRF wave with the cold plasma
approximation
In this study, the propagation and theabsorption property of the ICRF in the plasma
consisting of the helium as a majority ion andthe hydrogen as a minority ion, is investigatedby using the TASK3D/WM [1], which isdeveloped in the Kyoto University. The
standard vacuum magnetic field with magnetic
axis Rax =3.6 is used and its field strength atmagnetic axis is assumed to be 2.75 T. The

propagation of the ICRF wave is analyzed byusing the cold plasma approximation and theabsorption is calculated with the collision
dumping on resonance layers. The collision
dumping is assumed to be ×iThenthe absorption process of the ICRF wave does
not directly depend on the plasma parameter.
First, we investigate the absorption
property by changing the ICRF wave frequency
from 32 to 42 MHz in the 5% minority ion ratio.
Figure 1 shows the change of the absorption
power due to the frequency. In the Fig. 1, thevertical axis show the absorption power when
the antenna current is 1 A. In the Fig. 1, theabsorption power to the minority ion (H) is thelargest than others and the absorption power tohelium and electron is one tenth and one
hundredth of the minority ion's absorption
power, respectively. The absorption power near
39 MHz is the largest in each particle species.

Fig. 1 The dependence of the absorption power on theICRF wave frequency. The vertical axis show theabsorption power when the antenna current is 1 A. Red,green and blue lines are the absorption powers to H, Heand electron, respectively. Fig. 2 The contour of the absorption power profile (red)and resonance layer (green). In addition, Purple lines
show two-ion-hybrid resonance.
(a) ne=2x1019 m-3(b) ne=5x1019 m-3
Fig. 3 The dependence of the absorption power on theminority ion ratio. Red, green and blue lines are theabsorption powers to H, He and electron, respectively.

Figure 2 shows the absorption power
profile of ICRF wave in the 39 MHz. In the Fig.
2, the resonance layer in the 39 MHz is near
the saddle point of magnetic field strength
where the gradient of the magnetic fieldstrength is zero. ICRF wave is found to beabsorbed only near the resonance layer.
Next, we investigate the dependence of
the absorption power on the minority ion ratio
in the low density (electron density ne = 2x1019m-3) and relatively high density (ne = 5x1019 m-3).
Figure 3 shows the dependence of theabsorption power on the minority ion ratio in

the 39 MHz case. In the analyses with the cold
plasma approximation, the minority ratio in
the maximum absorption power is 30% in bothne = 2x1019 m-3 and ne = 5x1019 m-3. The
maximum value of the absorption power in thetwo case is alomst same. On the other hand,
except for near the minority ratio (30%) in themaximum absorption power, the absorption
power dependent on the density. In the higher
density case, the dependence of the absorption
power on the minority ion ratio is smaller thanthat in the low density case.
3. Summary
We analyzed the propagation and theabsorption property of the ICRF in the plasma
consisting of the helium as a majority ion andthe hydrogen as a minority ion by using thecold plasma approximation. As a result, theminority ratio with the maximum absorption
power is about 30% and the maximum
absorption power rarely changes by changing
the density in the analyses with the cold
plasma approximation. In the actual ICRF
experiments, plsamsa tempearture is expected
to enormously change due to the change of thedensity when the heat power of ICRF isconstant. To analyses the effect of the plasma
temperture on the propagation and theabsorption property of the ICRF with "hotplasma model" is an issue in the near future.
We will investigate the effect of theplasma temperuter by using the ray tracing
model as a first approach. In addition, thestrike points of the divertor change by
periodicallychangingthemagnetic
configuration and the average heat loaddecrease in the LHD long discharge. Thus, wewill investigate the effect of the magnetic
configuration on the propagation and theabsorption property in the future.
[1] A. Fukuyama and T. Tohnai, in 5th IAEA TechnicalCommittee Meeting on Alpha Particles in Fusion
Research, IAEA, Vienna, 1997.

