Speaker
Description
Instabilities of Alfvén eigenmodes (AEs) are of significant concern because they can enhance the cross-field transport of alpha particles beyond the neoclassical level in fusion plasmas. The threshold value of alpha-particle pressure for exciting AEs depends critically on the damping rate of AEs. The damping mechanisms include kinetic damping due to interactions with thermal particles, continuum damping due to Alfvén continuum crossing, and radiative damping due to emitting kinetic Alfvén waves (KAWs). The radiative damping is substantial and can even prevail in high-temperature burning plasmas. We revisit the radiative damping theory for TAEs in low-shear plasmas, considering TAE with an eigenfrequency near the bottom of the TAE gap.
In contrast to earlier papers, we provide the damping calculations in real space rather than Fourier space. In the real-space formalism, the Alfvén eigenmode represents a smooth radially localized source that emits a short-wavelength KAW. Unlike the source itself, the radiated wave is tractable via WKB approximation. The separation of spatial scales between the AE and KAW makes the radiative losses depend on this separation exponentially. This approach is straightforward technically and more enlightening from a physics standpoint for benchmarking numerical calculations of radiative damping.
| Presentation type | Oral |
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