Abstract Details
Abstracts
Author: Javier Maurino
Requested Type: Consider for Invited
Submitted: 2026-03-10 12:11:34
Co-authors: F.I. Parra , S.L. Newton, M. Barnes, I. Calvo, M. Landreman
Contact Info:
University of Oxford
Beecroft Building, Parks Road
Oxford, OX1 3PU
United Kingdom
Abstract Text:
Turbulence is generally not expected to drive a net parallel current in tokamaks because of a fundamental gyrokinetic symmetry that cancels flux-surface-averaged contributions. We show that controlled up–down asymmetry breaks this constraint and enables a turbulence-driven current that can become a leading-order effect.
In ITER-relevant plasmas, we find that turbulence in an up–down asymmetric tokamak can drive a current of order 10% of the bootstrap current, large enough to influence the current profile. Symmetry breaking promotes the effect from an O(rho_*^2) correction in symmetric configurations to an O(rho_*) contribution, making it the dominant turbulence-driven current enabled by asymmetry.
Surprisingly, the dominant contribution does not arise from correlations between density fluctuations and parallel electric-field fluctuations. Because these fluctuations produce only a Maxwell–Boltzmann electron density response, the electron contribution is suppressed by a factor equal to the square root of the electron-to-ion mass ratio. Instead, the primary mechanism involves ions: turbulence modifies the ion parallel flow, which subsequently alters the bootstrap current through electron–ion collisions.
These results are obtained from a first-principles multiscale framework coupling nonlinear gyrokinetic turbulence simulations with stella to a neoclassical drift-kinetic response computed with SFINCS. The effect is strongest at low collisionality, increases with up–down asymmetry, and is localised near mid-radius, where it may be large enough to modify the magnetic shear.
Characterization: 1.0
Comments: