Comparative Experiments on Lower Hybrid Wave Heating of Ions in High-Density Hydrogen and Deuterium Plasmas at the FT-2
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Comparative Experiments on Lower Hybrid Wave Heating of Ions in High-Density Hydrogen and Deuterium Plasmas at the FT-2 Tokamak S. I. Lashkula, *, A. B. Altukhova, A. D. Gurchenkoa, E. Z. Gusakova, V. V. D’yachenkoa, L. A. Esipova, V. A. Ivanova, O. A. Kaledinaa, M. Yu. Kantora, A. N. Konovalova, D. V. Kuprienkoa, M. I. Mironova, S. V. Shatalina, A. V. Sidorova, A. Yu. Stepanova, F. V. Chernysheva, and N. V. Tropina a Ioffe
Physical Technical Institute, St. Petersburg 194021 Russia *e-mail: [email protected]
Received March 4, 2020; revised April 9, 2020; accepted April 20, 2020
Abstract―In the framework of the isotope effect studies at the FT-2 tokamak, the efficiencies were compared of the lower hybrid wave heating of the ion components of the hydrogen and deuterium plasmas with high densities (close to the Greenwald limit, ne ≤ 1020 m–3). It was experimentally ascertained that, in accordance with the theoretical concepts, the efficient axial heating of the deuterium plasma ions occurs, as opposed to the peripheral heating of the hydrogen plasma ions. Such an isotope effect occurs due to the different localization of the plasma-RF wave interaction regions. The distinctive feature of these experiments is the fact that, in deuterium plasma, during the preliminary ohmic heating, the dependence of the energy lifetime on density τЕ(n) is linear (LOC dependence), and, with increasing density, the transition to the improved ohmic confinement mode occurs. In hydrogen plasma, on the contrary, the transition to the saturation mode is observed. In this study, the considerable decrease in τЕ was revealed, observed during the additional lower hybrid wave heating in both hydrogen and deuterium plasmas. Keywords: RF ion heating, isotope effect, parametric instabilities, plasma diagnostics DOI: 10.1134/S1063780X20090056
1. INTRODUCTION Unfortunately, the large-scale studies of the plasma ion component heating using the RF waves of the lower hybrid (LH) frequency range (Lower Hybrid Heating, LHH), performed in the 1970s and 1980s, did not result in the development of the reliable heating technique. In most experiments performed at different tokamaks, the considerable ion heating was not obtained. One of the reasons for this is the development of the parametric decay instabilities (PDIs) at the discharge periphery at densities exceeding a certain threshold value, which is accompanied by the acceleration of ions [1]. Only in a few experiments performed at the JFT-2, Wega, Petula-B, and FT-2 facilities, an increase in the ion temperature was observed [1, 2]. Since then, the research on the interaction between the LH waves and the tokamak plasmas is focused on the drag current generation, which is efficient only at relatively low plasma densities. In this work, in the case of dense plasma, an attempt is made to revise the efficiency of the LH plasma heating with allowance for the characteristic features revealed during the isotope effect studies.
In the experiment at the FT-2 tokamak (a = 0.08 m, R = 0.55 m, 19 k
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