About Possible Accumulation of Impurity Ions in the Island Region in Helical Plasma

Alexander SHISHKIN

Institute of Plasma Physics, National Science Center “Kharkov Institute of Physics and Technology”, Academicheskaya str.1, Kharkov-108, 61108, UKRAINE
And
Kharkov “V.N.Karazin” National University, Svobody sqr. 4, Kharkov-77, 61077, UKRAINE

Transport of the impurity ions can be described in the framework of Pfirsch-Schluter collision regime (MHD approach) and plateau regime (kinetic approach). In our study the flow trajectories as the solution of MHD equations (the paths of fluid elements) are considered. To obtain the flow trajectories of the impurity ions and main plasma ions Braginskij type equations are solved. These equations are solved analytically and numerically in the quasi-cylindrical coordinates for the toroidal helical magnetic field configuration. Numerical calculations are carried out for the magnetic configuration of the Large Helical Device with the inner shift of the magnetic axis. Effect of plasma pressure gradient ∇pα connected with the island formation on the flow trajectories is obtained. When the island exists (∇pα=0) the flow trajectories are concentrated at the periphery of plasma. If the island is absent (∇pα≠0) the flow trajectories penetrate in the core of plasma. The results of numerical calculation are compared with the analytical study conclusion [1]. In the numerical calculation the neon ions (20Ne10) are taken, which were the test ions in the experiment [2]. These physics results can be useful for the analysis of the experiments with the test impurity ions on Large Helical Device (National Institute for Fusion Science, Japan), where the island is formed for the diverter purposes [2]. The specific distribution of plasma parameters, namely the flattening of the plasma temperature profile throughout the island region is taken into account in our study. In our paper the physics explanation of the possible accumulation of impurity ions is proposed. One can see that the protection of the plasma core from the impurity ions in stellarators and helical devices becomes possible in the magnetic configuration with the island structure at the plasma periphery.

References

[1]. Shishkin, A. Wobig, H. Schneider, R. Igitkhanov, Y. Impurity Flows in Helical Plasma under the Resonant Magnetic Fields, 14th International Stellarator Workshop, Greifswald, September 2003.
[2]. Nakamura, Y., Takeiri, Y., Kumazawa, R., Osakabe, M., Seki, T. et al Plasma performance and impurity behavior in long pulse discharges on LHD, Nuclear Fusion 43 (2003) pages 219-227.


This work is partly carried out under the support of the Science and Technology Center in Ukraine, Project N 2313.