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Abstract
In magnetic confinement fusion reactor plasmas, the charged fusion products (such as alpha particles in deuterium-tritium plasmas) will be the dominant power source, and by controlling these charged fusion products using wave-particle interactions the reactor performance could be optimized. This thesis studies two candidate waves: Mode-Converted Ion Bernstein Waves (MCIBWs) and Alfvén Eigenmodes (AEs).
Rates of MCIBW-driven losses of alpha-like fast deuterons, previously observed in the Tokamak Fusion Test Reactor (TFTR), are reproduced by a new model so that the wave-particle diffusion coefficient can be deduced. The MCIBW power in TFTR is found to be [special characters omitted]1/3 that needed for collisionless alpha particle control. A reasonable reactor power scaling is derived.
To study AEs, existing magnetic fluctuation probes at the Joint European Torus (JET) have been absolutely calibrated from 30–500 kHz for the first time, allowing fluctuation measurements with [special characters omitted] and toroidal mode numbers [special characters omitted] using an 8-channel, 4-second, 1-MHz digitizer. Data analysis and database tools have been developed and applied to 4280 JET discharges using hydrogen, deuterium, tritium and helium-3. Three classes of AEs (driven by fast ions from various ion cyclotron range-of-frequency heating (ICRH) schemes) are identified. New AE phenomena are observed. AEs are less stable in “Optimised Shear” plasmas. AE “pitchfork splitting” (amplitude modulation) has been discovered. In other discharges, chaotic AE amplitude evolution and two types of explosive behavior have been discovered and found to be consistent with theoretical expectations. The strongest AEs appear to redistribute fast ions. No evidence for alpha-particle driven AEs has been found.
ICRH beatwaves are studied as a potential AE driver. The beatwave spectrum has been discovered to include multiple beat-frequency harmonies plus sums and differences of beat frequencies. AE excitation with beatwaves remains an area for future work. Data obtained incidentally regarding other plasma instabilities, including some of possible use for alpha particle control, are included for completeness.
Finally, an integrated alpha particle control experiment is suggested, including a candidate scenario for JET.
