Measurement of lower-hybrid current profile using interferometry and reflectometry methods at electron-cyclotron wave frequencies
A central problem in lower hybrid current drive is the effective penetration of the driven current in the plasma region; this is determined by several complicated mechanisms, such as wave power deposition resulting from multiple ray bounces and current diffusion. Substantial progress in the understanding of this issue can only be made if accurate and direct measurements of the radial profile of the rf-driven current density J(LH)(r) are performed. Two methods are discussed; the first is based on microwave transmissions along vertical chords at a frequency below the electron gyrofrequency and is appropriate for low-density plasmas. The second consists in measuring the attenuation of an ordinary mode reflected by the cut-off at the plasma frequency and is appropriate for high-density plasmas. Both methods exploit the proportionality between the local absorption coefficient for the LH tail at frequencies below the electron gyrofrequency and the parallel distribution function, which allows the inversion of the measured transmission spectra, yielding a value for J(LH)(r).
Bibliographic Reference: Paper presented: Radiofrequency Power in Plasmas, Oak Ridge (US), August 19-21, 1991
Availability: Available from (1) as Paper EN 36440 ORA
Record Number: 199210474 / Last updated on: 1994-12-02
Original language: en
Available languages: en