Abstract
Two-dimensional edge plasma structures of the l ≤ 2 helical system CHS have been investigated with the use of a neutral lithium beam probe. Two different types of edge magnetic configuration have been compared, namely, an inboard-wall limiter configuration and an ergodic magnetic divertor configuration which is intrinsic to non-axisymmetric helical devices. The scrape-off plasma in the limiter configuration is essentially one-dimensional and the radial scale length is well described by a simple diffusion model with finite connection length of the magnetic field line. While in the ergodic divertor configuration, edge plasma structure shows up-down asymmetry in the steady state near the outer separatrix region regardless of the symmetric magnetic structure. The asymmetry reverses when the magnetic field direction is reversed. Plasma shift is apparently in the direction of ion B × ∇B drift. The result suggests that plasma equilibrium in the ergodic layer is not determined simply by the magnetic field structure. The effect of plasma flow and drift motions would be important. Such asymmetry in plasma structure may induce non-uniform heat deposition on the divertor plates. Modelling of plasma equilibrium in the ergodic layer is necessary for practical helical divertor design.
| Original language | English |
|---|---|
| Article number | 002 |
| Pages (from-to) | 251-256 |
| Number of pages | 6 |
| Journal | Nuclear Fusion |
| Volume | 47 |
| Issue number | 4 |
| DOIs | |
| Publication status | Published - Apr 1 2007 |
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All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Condensed Matter Physics
Cite this
Two-dimensional plasma structure in the edge region of the compact helical system. / Nakamura, K.; Iguchi, H.; Schweinzer, J.; Shimizu, A.; Isobe, M.; Takahashi, C.; Nishimura, S.; Suzuki, C.; Yoshimura, Y.; Nagaoka, K.; Minami, T.; Akiyama, T.; Ida, K.; Matsuoka, K.; Okamura, S.
In: Nuclear Fusion, Vol. 47, No. 4, 002, 01.04.2007, p. 251-256.Research output: Contribution to journal › Article
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TY - JOUR
T1 - Two-dimensional plasma structure in the edge region of the compact helical system
AU - Nakamura, K.
AU - Iguchi, H.
AU - Schweinzer, J.
AU - Shimizu, A.
AU - Isobe, M.
AU - Takahashi, C.
AU - Nishimura, S.
AU - Suzuki, C.
AU - Yoshimura, Y.
AU - Nagaoka, K.
AU - Minami, T.
AU - Akiyama, T.
AU - Ida, K.
AU - Matsuoka, K.
AU - Okamura, S.
PY - 2007/4/1
Y1 - 2007/4/1
N2 - Two-dimensional edge plasma structures of the l ≤ 2 helical system CHS have been investigated with the use of a neutral lithium beam probe. Two different types of edge magnetic configuration have been compared, namely, an inboard-wall limiter configuration and an ergodic magnetic divertor configuration which is intrinsic to non-axisymmetric helical devices. The scrape-off plasma in the limiter configuration is essentially one-dimensional and the radial scale length is well described by a simple diffusion model with finite connection length of the magnetic field line. While in the ergodic divertor configuration, edge plasma structure shows up-down asymmetry in the steady state near the outer separatrix region regardless of the symmetric magnetic structure. The asymmetry reverses when the magnetic field direction is reversed. Plasma shift is apparently in the direction of ion B × ∇B drift. The result suggests that plasma equilibrium in the ergodic layer is not determined simply by the magnetic field structure. The effect of plasma flow and drift motions would be important. Such asymmetry in plasma structure may induce non-uniform heat deposition on the divertor plates. Modelling of plasma equilibrium in the ergodic layer is necessary for practical helical divertor design.
AB - Two-dimensional edge plasma structures of the l ≤ 2 helical system CHS have been investigated with the use of a neutral lithium beam probe. Two different types of edge magnetic configuration have been compared, namely, an inboard-wall limiter configuration and an ergodic magnetic divertor configuration which is intrinsic to non-axisymmetric helical devices. The scrape-off plasma in the limiter configuration is essentially one-dimensional and the radial scale length is well described by a simple diffusion model with finite connection length of the magnetic field line. While in the ergodic divertor configuration, edge plasma structure shows up-down asymmetry in the steady state near the outer separatrix region regardless of the symmetric magnetic structure. The asymmetry reverses when the magnetic field direction is reversed. Plasma shift is apparently in the direction of ion B × ∇B drift. The result suggests that plasma equilibrium in the ergodic layer is not determined simply by the magnetic field structure. The effect of plasma flow and drift motions would be important. Such asymmetry in plasma structure may induce non-uniform heat deposition on the divertor plates. Modelling of plasma equilibrium in the ergodic layer is necessary for practical helical divertor design.
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U2 - 10.1088/0029-5515/47/4/002
DO - 10.1088/0029-5515/47/4/002
M3 - Article
AN - SCOPUS:34047093533
VL - 47
SP - 251
EP - 256
JO - Nuclear Fusion
JF - Nuclear Fusion
SN - 0029-5515
IS - 4
M1 - 002
ER -