Interaction of lower hybrid waves with thermonuclear alpha particles in tokamak reactor

A brief quantitative evaluation is presented of the absorption of the lower hybrid wave on the resonance with high overtones of the cyclotron motion in the ITER tokamak, which is an international tokamak reactor project. Fusion of tritium and deuterium nuclei producing 3.5 MeV alpha particles should take place in the tokamak reactor. The cyclotron motion radius for these particles in the tokamak's magnetic field (∼ 5T) is substantially higher than the wavelength of the lower hybrid wave, and this is what makes possible absorption of that wave on the resonance ω=nωc (ω is the frequency of the wave and ωc is the cyclotron frequency of the alpha particles; n>>1). The resonance is unwanted because it withdraws energy of waves destined for electrons forming the toroidal electric current. Theory demonstrates that the absorption of lower hybrid waves by alpha particles drops rapidly if their frequency is increased to above a critical value fk. This value depends on the plasma density, magnetic field intensity and alpha particle energy. The results of computer modeling of the effect of alpha particles on the current generation by lower hybrid waves are described. A quite new finding concerned the existence of accelerated particles with an energy exceeding 10 MeV, which contribute substantially to the unwanted absorption of waves. The ratios of powers absorbed on alpha particles and on electrons were also determined for the ITER project. At a frequency of 4 GHz the ratio is about 10%, whereas at frequencies ≥ 5 GHz it is negligible. (Z.S.). 3 figs., 4 refs