A method for measuring the direction of the magnetic field in a Tokamak plasma by laser light scattering

For scattering wavenumbers k such that alpha =(1/k lambda D) > Omega e, that resolution of the spectrum shape by conventional means is not possible. It is shown in this paper that the peaks are superimposed when the scattered light is passed through a Fabry-Perot etalon of free spectral frequency range equal to the electron cyclotron frequency. The resulting modulation, and consequently the effect of the magnetic field, can then be detected even with a ruby laser source.