Non-linear interaction of Alfven waves with fast particles
- Univ. of Nottingham, University Park (United Kingdom)
- JET Joint Undertaking, Abingdon, Oxon (United Kingdom); and others
Concern surrounds instabilities driven by fast particles in large tokamaks and their possible consequences for particle transport. This has motivated the development of HAGIS which is a numerical code capable of calculating the power transfer from a hot-particle source to a spectrum of Alfven waves, and the ensuing non-linear wave evolution, up to and following saturation. Fast particle motion is treated using a guiding center Hamiltonian description, whilst the wave evolution uses a Lagrangian formulation for shear Alfven waves. The system utilizes straight field line coordinates with the Jacobian chosen to simplify the equations of motion. The magnetic field is modelled as the superposition of an axisymmetric toroidal field and a set of time dependent electro-magnetic perturbations, with the perturbed fields accorded two degrees of freedom corresponding to their amplitudes and phase shifts. The model accounts for nonlinear wave-particle interactions, which is dominant for weakly-driven systems, but ignores MHD wave-wave nonlinearities. Hence the linear mode structure can be taken directly from linear calculations with the CASTOR normal mode code. Numerical noise in the system is reduced by only considering those particles present in the system which constitute the change in the fast particle distribution function, this being the so-called {delta}f technique. As the physical system evolves the fast particle distribution flattens through a transfer of free energy to the unstable wave spectrum. The growth in wave amplitude eventually leads to a modification of particle orbits and ultimately to the wave itself saturating. With the HAGIS code the linear wave growth rates and self-consistent saturation amplitudes can be determined for arbitrary geometry and for realistic trapped and passing particle distributions. Results from HAGIS will identify regions of enhanced diffusion in the presence of fixed and varying amplitude TAEs, and indicate possible loss mechanisms.
- OSTI ID:
- 489440
- Report Number(s):
- CONF-960354-; TRN: 97:011586
- Resource Relation:
- Conference: International Sherwood fusion theory conference, Philadelphia, PA (United States), 18-20 Mar 1996; Other Information: PBD: 1996; Related Information: Is Part Of 1996 international Sherwood fusion theory conference; PB: 244 p.
- Country of Publication:
- United States
- Language:
- English
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