The general problem of ray tracing in the electron cyclotron range of frequencies is reviewed with the view of applying geometrical optics techniques to microwave heating in ECR device. The usual formulation of geometrical optics which breaks down at ECR region is presented. A consistent eikonal expansion is presented which is valid near ECR region for cases in which the waves are weakly damped. The ray tracing code, RAY, which was developed for master thesis is described.. Ray tracing in plane stratified plasma geometries is discussed. The application of ray tracing techniques to ECR device is discussed and the calculated rays of the KAIST ECR device is presented.
