H. Takamura

M. Okamoto

R. Kanno

S. Jimbo

National Institute for Fusion Science (NIFS-Repository)

• §9. Stri ke Po int Pattern on Loca l Island D ivertor Head Kanno, R., limbo, S., Takamura, H. (Chubu Univ.), Okamoto, M . The Local Island Divertor (LID) is one of the diver-tor concepts in the Large Helical Device (LHD) configu-ration [I, 2]. and it utilizes an m/n= I / 1 island formed at the edge region of the LHD. Control of the edge plasma by means of the LID is expected to realize the high temperatme divertor operation (HT-operation). In t he HT-operatiol1) the neo-classical effect on the transport becomes important. The Monte Carlo simulation based on the test par-ticle representation has an ad vantage of appropriately treating the edge plasma transport in the three-dimensional field line structure with the island aJld ergodic zones [3]. We trace the orbits of the guiding centers of the test par-ticles in tbe fixed magnetic field under the effects of the Coulomb collision [3], in order to numerically observe tbe distribution of tbe guiding centers in t he configu-ration space. Here the vacuum magnetic field is used to calculate the orbits, the magnetic axis is located at Ii{) = 3.6 m and the strength of magnetic field at t he axis is Bo = 3 T . Consider the situation that the test particles are mono-energetic protons with Et = 300 eV, the distr ibution of the initial pitch angles of the parti-cles is uniform: and the Maxwellian background plasma is uniform in the edge region including the island. When the collision frequency of the edge plasma is estimated as v = 8.4 X 103 S~l, we find t hat the strike point pattern is caused by the diffusion to the outside of the torus and the peak of the strike point distribu-tion is located at t he edge of the head, as shown in Fig. 1. On the other hand, when the collision frequency be-comes small and it is estimated as v = 9.0 X 102 5- 1 , the strike point pattern is changed as shown in Fig. 2. Distribntions of t he cosine of pitch angles vII/ lvl of t he test particles striking on the head are given in Fig. 3. References [I] Komori, A. et a!. : P lasma Physics and Controlled Fusion Research , 1994 (IAEA, 1995). [2] Ohyabu , N. et a!. : J. Nuc!. Mater. 220-222 (1995) 298. [3] Kanno, R. , Jimbo, S. , Takamaru H. and Okamoto, M. : accepted for publication in J. Plasma F\,sion Res. SERlES 6. Figme I : Strike point pattern for v = 8.4 X 103 S~l Figure 2: Strike point pattern for v = 9.0 X 102 S~I. ;-0.15 ,--~--~--~----, ••••. (a) - (b) $ 0.\0 -- (c) 5 -,: = .Q :E 0.05 ~ :;; 0.00 L-_~'="""""""..-,,,,,,~ _ _ ..c' ·\.0 -0.5 0.0 0.5 1.0 v" I I v I Figure 3: Distributions of the cosine of pitch angles vII/lvl. (a) dotted line: v = 7.8 X 104 S~l , (b) solid line: v = 8.4 X 103 S~l and (c) dashed line: v = 9.0 X 102 5- 1 . 185 

Strike Point Pattern on Local Island Divertor Head

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