Optical design of the oblique ECE antenna system for JET

Systematic disagreements between ECE and Thomson Scattering diagnostics observed in various fusion devices led to the proposal of the so called Oblique ECE diagnostics on JET. This system will allow the study of the electron distribution function at low energies to reveal deviations from the Maxwellian distribution. This paper is devoted to the design of the quasi optical antenna for this diagnostics. The physical bases of the diagnostics imply two lines of sight at about 10° and 20° respectively from the magnetic field gradient. Severe geometrical constraints are imposed by the location of the antenna. The design strategy and physical optics calculations used to validate it are presented.