Speaker
Description
Several fusion devices have been implemented second harmonic dispersion interferometer, which has been used to measure the line-integrated electron density (LIED). This diagnostic technique, which will be analyzed here in its homodyne implementation, is based on a laser beam which propagates through the plasma collinearly with the beam converted into one of its harmonics, typically the second-harmonic. Being the plasma a dispersive medium, the beams are subject to different phase shifts from which it is possible to retrieve the plasma free electron density.
In this study, we propose the simultaneous use of more up-converted beams to collinearly probe the plasma at the same time. A third-harmonic beam may propagate collinearly to the fundamental and second-harmonic converted laser, with a small increase in the complexity of the setup. The use of more harmonics makes this device more robust to fringe skips and increases the robustness of the measurement. However, the low conversion efficiency of nonlinear crystals for higher-order harmonic generation remains one of the primary challenges to be addressed.
The main advantages and issues of this proposed setup will be discussed. Estimations of the raw and processed signals in a typical fusion device scenario will be presented, together with a schematic of a possible implementation of this diagnostic.