K. Ichiguchi

M. Okamoto

N. Nakajima

O. Motojima

National Institute for Fusion Science (NIFS-Repository)

§3. Bootstrap Current of LHD with Multi Layer Helical Coils lchiguchi, K., Nakajima, N., Okamoto, M., Motojima, 0. Each helical coil in the LHD is composed of three layers which are called the outer (0) , the mid (M) and the inner (I) layers. In the standard configuration corresponds to lc = 1. 25, aU three layers are used for generating the confinement magnetic field, where {c = 1.25. If only the 0-layer is used, the radius of the heli-cal coil becomes large and {c increases to 1.38, while {c decreases to 1.12 in the case of only the !-layer. Here we estimated the bootstrap current based on the neoclassical transport theory. In · this case, the bootstrap current is calculated consistenltly with the three-dimensional MHD equilibria by iterating the calculations of the MHD equilibrium and the estimation of the net toroidal current alternatively1>. Here it is as-sumed that both the electrons and ions should be in the 1 I v collisional regime and the den-sity and the temperature of the ions and the electrons should be the same. The density is fixed as ni = ne = 0. 5 X 1020 ( 1 - <I>) ( m - 3), ( 1) where <I> denotes the normalized toroidal mag-netic flux. The temperatures have the same profile of Ti = Te = To(1 -<I>), (2) however, the factor of To is adjusted to obtain the specified beta value. In this case, the boot-strap current hscan be estimated by2> h.,(<'P) = -27T J d<'PGbs x ( £31 ~= + (L;2 + L;2n :~) /(B2), (3) 132 where n = ni = ne and T = Ti = Te. Gbs is so-called the geometrical factor which is calcu-lated with the information of the equilibriu1n magnetic field calculated by the Vl«EC code. Since we assumed that all particles should be in the 1 I v regime, L31 and L 32 are proportional to the fraction of the trapped particles which can be also counted with the structure of equi-librium magnetic field. Figure 1 shows the profiles of the bootstrap currents of the three types of {c = 1.12, 1.25 and 1.38 at /30 = 2%. It is seen that the current in the standard configuration with lc = 1. 25 is larger than those. in {c =1.12 and 1.38. Here it should be noted that the magnetic field in the standard configuration is about three times of those in other configurations because the cur-rent flowing inside the helical coil is propor-tional to the number of the layers. Therefore, the pressure in the equilibrium of the standard configuration is nine times of the others at the same beta value. ~ 12 ....... 10 ~ 8 u 6 f 0 ~ Fig.1 Bootstrap current for {c = 1.38, 1.25 and 1.12. References 1) Watana.be,K., et al. : Nucl.F\1sion 32 (1992) 1499. 2) Nakajima,N., et al. : J.Phys.Soc.Jpn. 61 (1992) 833. 

Bootstrap Current of LHD with Multi Layer Helical Coils

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