Chirping and turbulence in tokamak plasmas

Motivation

• Chirping AEs indicate non-perturbative EP-induced dynamics; it is seen a lot experimentally
• Status: most of simulations using hybrid codes (e.g. HMGC)
• Challenge:

1. Is it possible to get chirping modes using gyrokinetic codes?
2. Is it possible to run chirping mode in presence of turbulence?
3. What turbulence does to chirping? (“turubulent scattering” etc)

Chirping of AEs without turbulence

Circular tokamak with $q(s) = 1.5 + s^2$ (shear larger than ITPA).

TAE evolution at fpart = 1.0%: low drive, no chirping
Example of chirping: fpart = 2.0%
Evolution of fast-ion density
Evolution of electrostatic potential (poloidal harmonics)
Evolution of electrostatic potential (poloidal cross-section): circles corrspond to accumulation points of the SAW continuum

Chirping of AEs including turbulence

ITPA geometry $q(s) = 1.71 + 0.15 s^2$: low shear => no chirping in the absence of turbulence!

Heat flux and bulk-plasma temperature profile evolution by combined nonlinear ITG-TAE-EPM

Evolution of n=2 toroidal component: weak chirping
Evolution of n=6 toroidal component: strong chirping: mode moves to radial location where its frequency matches $\omega_A$
Electrostatic potential (poloidal cross-section)

Outlook

see work started by Christoph and Xin