Self-driven current generation in turbulent fusion plasmas

Abstract

Global gyrokinetic simulations with self-consistent coupling of neoclassical and turbulent dynamics show that turbulence can significantly affect plasma self-driven mean current generation in tokamaks. The current amplitude, profile and associated phase space structures can all be modified. Turbulence can significantly reduce the current generation in the collisionless regime, generate current profile corrugation near the rational magnetic surface and nonlocally drive current in the linearly stable region—all these are expected to have a radical impact on broad tokamak physics. Both electron parallel acceleration and residual stress from turbulence play crucial roles in turbulence-induced current generation.

Gyrokinetic simulations of electric current generation in ion temperature gradient driven turbulence

“…5 The current driven by turbulence has been discussed in detail using the analytical and numerical approaches. 3,4,[6][7][8][9][10] It has been shown by S. -I. Itoh and K. Itoh firstly with a slab model. 6 Driftwave fluctuations drive a net current when k is finite, where k is the averaged parallel wave number over the spectrum .…”

“…The spontaneous variation of electron momentum provides a current source which corrugates the current density profile and has significant impacts on the generation of the plasma self-driven mean current. 3,4 The current induced by turbulence affects the MHD instabilities which can provide a way to study the interaction between the turbulence and the MHD instabilities.…”

“…A direct calculation of electron and ion current generation by ITG and CTEM turbulence was reported in early global the turbulence acceleration is discussed by Wang. 4 The electrostatic studies by Yi 9 show that the net current induced by electron temperature gradient turbulence is approximately 20% of the local bootstrap current density. Most previous simulations of the current flow generation in tokamak plasmas are based on the long wave-length approximation in the quasi-neutrality equation, and the fine structures of the turbulence driven current have not been thoroughly investigated.…”

Observation of a new type of self-generated current in magnetized plasmas

“…For decades since the invention of the tokamak, various external or self-generated current drive mechanisms have been developed for steady-state operations, such as radio frequency-driven, neutral beam injection (NBI)-driven, and bootstrap current. Recently, it was found that micro-instabilities can also generate or modify the plasma current 1 – 4 , which could probably explain an anomaly in the current profile found in experiments such as in the hybrid operation scenario 5 . The self-generated current drive mechanisms have been predicted in theories 1 , 2 , 4 , 6 , then discovered in experiments 7 – 9 and they were found to be consistent with each other.…”

“…Recently, it was found that micro-instabilities can also generate or modify the plasma current 1 – 4 , which could probably explain an anomaly in the current profile found in experiments such as in the hybrid operation scenario 5 . The self-generated current drive mechanisms have been predicted in theories 1 , 2 , 4 , 6 , then discovered in experiments 7 – 9 and they were found to be consistent with each other.…”