Evidence for Regions of Nearly Suppressed Velocity Space Diffusion Caused by Finite Larmor Radius Effects during ICRF Heating
During high power heating with waves in the cyclotron range of frequencies (ICRF), the distribution function of the resonating ions becomes non-Maxwellian and an anisotropic tail develops mainly in the perpendicular velocity direction. The evolution of the distribution function can be described by a quasi-linear diffusion operator in phase space. Owing to finite Larmor radius (FLR) effects, the diffusion coefficient in this operator varies with the gyro-radius normalized with the wavelength. At certain ion energies the diffusion coefficinet can become strongly reduced, effectively preventing resonating ions from reaching higher energies. In this article we report on measurements which show a significant difference in the distribution function between different scenarios for heating of hydrogen ions in JET. Comparison with theoretical calculations show that these differences can be explained by higher-order FLR effects on velocity space diffusion during ICRF heating. The importance of these effects on the power deposition is also emphasized.
Bibliographic Reference: Article: Evidence for Regions of Nearly Suppressed Velocity Space Diffusion Caused by Finite Larmor Radius Effects during ICRF Heating, JET-P(98)38
Record Number: 199910793 / Last updated on: 1999-05-28
Original language: en
Available languages: en