Ray tracing is used in a periodically inhomogeneous cylindrical plasma to demonstrate the importance for lower-hybrid (LH) wave propogation of the magnetic ripple caused by the discrete nature of the toroidal-field coils in a tokamak. It is shown that magnetic ripple may induce Hamiltonian chaos in the ray motion and thus lead to strong variations in the component of the wave vector parallel to the equilibrium magnetic field. Therefore magnetic ripple can be effective in bridging the spectral gap typical of LH current drive and can greatly affect the LH wave accessibility to the plasma center.

• Received 10 June 1994

DOI:https://doi.org/10.1103/PhysRevLett.75.1308