Growth rate for core-localized toroidal Alfven eigenmodes
- Univ. of Texas, Austin, TX (United States)
- JET Joint Undertaking, Abingdon, Oxfordshire (United Kingdom)
Unstable core-localized modes may occur in the central region of an ignited plasma since the alpha particles are most plentiful here. Evidence of core-localized modes has apparently been found in a D-D plasma in TFIR, with fast ions produced by ion-cyclotron heating. In the reversed-shear mode of operation, these modes could become prevalent. NOVA-K simulations by G. Y. Fu, reported at the 1995 DPP/APS Meeting find such instability, but only when the shear is rather weakly reversed, in order for the radiative and continuum damping to be minimized. Recent work has, in fact, demonstrated the existence of an enlarged spectrum of ideal toroidal Alfven eigenmodes within a toroidicity-induced Alfven gap when the inverse aspect ratio is comparable to or larger than the value of the magnetic shear, which limit is appropriate for the low-shear region in most tokamaks, especially those with low aspect ratio {open_quotes}spherical tokamaks{close_quotes}. This feature might facilitate the consideration of low-shear modes for the purpose of investigating Alfven-type instability properties in present-day deuterium/tritium experiments and future such devices (e.g., ITER). Non-ignition experiments that can use external antennae to excite and study Alfven eigenmodes may be able to observe this multiplicity of core-localized modes. Two-dimensional codes for TAE stability analysis of fusion plasmas should also confirm this result. Due to their broadened width, the new modes may be destabilized by alpha particles more easily than the standard toroidal Alfven eigenmodes. Here we calculate the growth rate for these modes. The stability threshold can then be examined by a comparison of the growth rate with estimates for various appropriate damping rates.
- DOE Contract Number:
- FG03-96ER54346
- OSTI ID:
- 489470
- Report Number(s):
- CONF-960354--
- Country of Publication:
- United States
- Language:
- English
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