TOKAMAK PLASMA DIAGNOSIS BY ELECTRICAL PROBES

This paper reviews progress in the understanding and application of electrical probes for the diagnosis of tokamak edge plasmas. Langmuir probes are still one of the most commonly applied diagnostics in tokamaks but our understanding of how to interpret them in strong magnetic fields is still rather limited. Recent results from flush-mounted Langmuir probes in divertor plates are used to highlight the problem areas, in particular non-saturation of the ion current and low electron to ion saturation current ratios. The importance of measuring the parallel flow velocity in the plasma edge is highlighted and recent developments in theories for interpretation of Mach probes are discussed. Finally, the importance of diagnostics for ion temperature and impurity content is emphasized, and progress in the application of advanced electrical probes such as retarding field analysers and mass spectrometers to the tokamak boundary is reviewed in this context.