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arXiv · 2610.28424

Exponential Growth of Turbulent Cross Helicity in Shear-Flow-Driven Turbulence

B. Tripathi·A. E. Fraser·P. W. Terry·E. G. Zweibel·M. J. Pueschel·A. M. Beloborodov
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Abstract

Cross helicity, the velocity--magnetic-field correlation, is an ideal invariant of incompressible magnetohydrodynamics and constrains energy cascades and magnetic-field generation. Although cross helicity typically decays via visco-resistive effects, we analytically demonstrate that it grows exponentially in sheared inhomogeneous turbulence. This cross-helical shear instability is confirmed using three-dimensional numerical simulations. Growth requires a nonzero gradient of the Reynolds--Maxwell stress to produce turbulent cross helicity; this production overcomes effective losses when shear exceeds a threshold set by the ratio of turbulent magnetic to momentum diffusivities.

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B. Tripathi, A. E. Fraser, P. W. Terry, E. G. Zweibel, M. J. Pueschel, A. M. Beloborodov. 2026-10-20. Exponential Growth of Turbulent Cross Helicity in Shear-Flow-Driven Turbulence. https://arxiv.org/abs/2610.28424

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