NIFS-059

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Author(s):

A.Fukuyama, S.-I.Itoh, K.Itoh, K.Hamamatsu, V.S.Chan, S.C.Chiu, R.L.Miller and T.Ohkawa

Title:

Nonresonant Current Drive by RF Helicity Injection

Date of publication:

Oct. 1990

Key words:

helicity injection, current-drive, rf helicity, nonresonant force

Abstract:

Current drive via nonresonant interaction between RF waves and plasma is studied by using the kinetic wave analysis and computation in a stationary state. The nonresonant interaction generates a force, in addition to the usual ponderomotive force. The force of our concern mainly acts as an internal force among plasma species; the net momentum input from the wave to the plasma is small in this process. The current driven by this process is not included in the conventional current drive scheme (i.e. resonant absorption of the parallel wave momentum or wave energy), and appears associated with the change of the RF wave helicity l<tilde{A}¡¦r>tilde{B}. The analysis is applied to ICRF waves in large tokamaks. The one dimensional wave analysis code (TASK/W1) shows that the conversion ratio of the RF wave helicity to the DC helicity becomes close to one in the case of hot plasmas . The current drive efficiency by the RF helicity injection is not necessarily bounded by the conventional RF current drive efficiency. Preliminary study suggests that it scales strongly with electron temperature and toroidal magnetic field but only weakly with plasma density.

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