Large probes in tokamak scrape-off plasmas. Analytic model for the collisionless scrape-off plasma

When large probes are used to measure plasma properties in tokamak scrape-off layers, the presence of the probe influences the plasma being measured. A theory is presented for probe interpretation which makes it possible to infer undisturbed values of Te, Ti, ne, etc. The first requirement in such an analysis is for analytic models of the scrape-off layer, which can then be modified to allow for the presence of the probe. The present work gives such a model for the collisionless scrape-off layer, and criteria are stated governing its applicability. Such models may be of use for other applications, e.g., predictions of power loading to limiter surfaces, the magnitude of wall sputtering, etc.