The role of reconnection in magnetized turbulence

Magnetic reconnection has long been hypothesized to be a key ingredient of magnetized plasma turbulence, but a theory of how it might occur had been lacking. Recent analytical works [Loureiro17a, Mallet17a, Boldyrev17] have revisited the current understanding of Alfvénic turbulence, concluding that reconnection must inevitably become important in the inertial range, at the scale where it becomes faster than the eddy turn over time. This is predicted to lead to a transition to a new sub-inertial interval, suggesting a route to energy dissipation that is fundamentally different from that envisioned in the usual Kolmogorov-like phenomenology.

These concepts can be extended to weakly collisional plasmas, where reconnection is enabled by electron inertia rather than resistivity [Loureiro17b, Mallet17b]. Although several different cases must then be considered (whether the eddies themselves are on MHD or kinetic scales, whether the plasma beta is large or small, etc.), a common result to all of them is that the energy spectrum exhibits a scaling with the perpendicular wave number that scales between $k_\perp^{−8/3}$ and $k_\perp^{−3}$, in favorable agreement with observations and numerical studies.

These results have since found support in direct numerical simulations [Walker18, Dong18] and observations of solar wind turbulence [Vech18]. This talk aims to review these results, and discuss their implications.

References:

[Boldyrev17] S. Boldyrev and N.F. Loureiro, Astrophys. J. 844, 125 (2017)
[Dong18] C. Dong, L. Wang, Y.-M. Huang, et al., Phys. Rev. Lett. 121, 165101 (2018)
[Loureiro17a] N.F. Loureiro and S. Boldyrev, Phys. Rev. Lett. 118, 245101 (2017)
[Loureiro17b] N.F. Loureiro and S. Boldyrev, Astrophys. J. 850, 182 (2017)
[Mallet17a] A. Mallet, A. A. Schekochihin and B.D.G. Chandran, Mon. Not. R. Astron. Soc. 468, 4862 (2017)
[Mallet17b] A. Mallet, A. A. Schekochihin and B.D.G. Chandran, J. Plasma Phys. 83, 905830609 (2017)
[Vech18] D. Vech, A. Mallet, K. G. Klein, et al., Astrophysics. J. Lett. 855, L27 (2018)
[Walker18] J. Walker, S. Boldyrev, N. F. Loureiro, Phys. Rev. E 98, 033209 (2018)