Multi-scale interactions between turbulence and magnetohydrodynamic instability driven by energetic particles

Abstract

In order to realize high performance burning plasmas in magnetic-confinement fusion devices, such as tokamaks, both bulk plasma transport and that of energetic fusion alpha-particles, which result from different scale fluctuations with different free energy sources, have to be reduced simultaneously. Utilizing the advantage of global toroidal non-linear simulations covering a whole torus, here, we found a new coupling mechanism between the low-frequency micro-scale electromagnetic drift-wave fluctuations regulating the former, while the high-frequency macro-scale toroidal Alfven eigenmode (TAE) regulates the latter. This results from the dual spread of micro-scale turbulence due to the macro-scale TAE not only in wavenumber space representing local eddy size but also in configuration space with global profile variations. Consequently, a new class of turbulent state is found to be established, where the turbulence is homogenized on the poloidal cross-section with exhibiting large-scale structure, which increases fluctuation levels and then both transports, leading to deterioration in the fusion performance.

Multi-scale turbulence simulation suggesting improvement of electron heated plasma confinement

“…Therefore, interactions between energetic particles and TEM/ETG turbulence are expected to be weak. When we consider interplay from electron to ion-scale turbulence and macroscopic fluctuations, magnetohydrodynamic instability driven by energetic particles will become a candidate for the third player 43 , which is a theoretically and numerically challenging subject.…”

Nonlinear interaction of Alfvénic instabilities and turbulence via the modification of the equilibrium profiles

“…For comparison, note that in Ishizawa et al. (2021). The electron thermal to magnetic pressure ratio of (with being the volume averaged electron density).…”

“…Here, like in the EPS-2019 case, we choose a value of ρ * similar to the CYCLONE base case (originally chosen as an international benchmark case for ITG turbulence in a DIII-D configuration): ρ * = ρ s /a = 0.00571 (therefore, Lx = 2/ρ * = 350). For comparison, note that ρ * = 1/100 in Ishizawa et al (2021). The electron thermal to magnetic pressure ratio of β e = 8π n e T e (ρ r )/B 2 0 = 5 × 10 −4 (with n e being the volume FIGURE 1.…”

“…2021; Ishizawa et al. 2021). Different mechanisms can be responsible for the interaction of EPs and turbulence.…”

“…Flux-tube numerical simulations have also been performed (see for example Angioni et al 2009;Bass & Waltz 2010;Zhang et al 2010;Citrin et al 2013;Garcia et al 2015;Di Siena et al 2019). Finally, in the last few years, we have also been able to perform global electromagnetic numerical simulations (Biancalani et al 2019(Biancalani et al , 2021Di Siena et al 2021;Ishizawa et al 2021). Different mechanisms can be responsible for the interaction of EPs and turbulence.…”