Current drive by beat waves in tokamak plasmas

Abstract

Current drive in tokamak plasmas by a beat wave is considered in 2D geometry. The beat wave is excited by the nonlinear interaction of two intense microwave pulses (free‐electron lasers) in the plasma. The three wave nonlinear interaction equations in steady state are solved numerically for this purpose. The 2D toroidal effect and the effect of finite spatial width of the pump microwave pulses are taken into account. To illustrate the principle, two types of tokamak are considered: one is small, typical of MTX, and the other one is larger, such as JET. In both cases, it is found that a good beat wave coupling exists for a Langmuir beat wave with a phase velocity of around 2.0 to 4.0 times the thermal velocity of the electrons. It has also been found that about 26–32% of the total input power of the pump microwaves is deposited in the beat wave. In these cases, there is almost complete pump depletion of the higher frequency pump microwave and the beat wave is completely damped on the plasma electrons withi...