Speaker
Description
Transport of alpha-particles born in deuterium-tritium (D-T) nuclear fusion reactions is a key issue for magnetic fusion. Wave-particle resonant interactions – between Alfvén waves and alpha-particles born at super-Alfvénic energy – could induce significant radial re-distribution of alpha-particles, affecting both the self-heating efficiency and integrity of the first wall [1].
The effect of high thermal plasma pressure gradients on the existence of toroidal Alfvén eigenmodes (TAEs), which was first considered theoretically in [2], could potentially present a very attractive option for resolving the concerns raised by the presence of TAEs in burning fusion plasmas. This effect is not associated with an increase in TAE damping caused by kinetic interactions, but is due rather to the fact that ideal MHD TAEs cease to exist above a certain critical plasma pressure gradient. Here we investigate the thermal plasma pressure effect on Elliptical Alfvén Eigenmodes (EAEs) – which could be particularly important for the spherical tokamak route to fusion since these devices have high natural ellipticity e and high normalized pressure.
Numerical investigations performed using the MISHKA MHD eigenvalue code on JET and ST40-like discharges reveal a higher critical pressure gradient for the non-existence of EAEs than that of TAEs. Building on the analysis of [3,4], a new analytic theory applicable to core-localised EAEs and developed in the limit e/S >>1 (where S is magnetic shear) will be presented.
[1] ITER Physics Expert Group on Energetic Particles, Heating and Current Drive and ITER Physics Basis Editors Nucl. Fusion 39, 2471 (1999)
[2] Fu G Y and Cheng C Z 1990 Physics of Fluids B: Plasma Physics 2 985–993
[3] Berk H L et al 1995 Physics of Plasmas 2 3401
[4] Candy et al Physics Letters A 215 (1996) 299
This work has been funded by the EPSRC Fusion Grant 2022/27 [grant number EP/W006839/1]. We thank Michael Fitzgerald, Daniele Brunetti and Ken McClements for several helpful comments.