Thresholdless stochastic particle heating by a single wave.

Stochastic heating is a well-known mechanism through which magnetized particles may be energized by low-frequency electromagnetic waves. In its simplest version, under spatially homogeneous conditions, it is known to be operative only above a threshold in the normalized wave amplitude, which may be a demanding requisite in actual scenarios, severely restricting its range of applicability. In this paper we show, by numerical simulations supported by inspection of the particle Hamiltonian, that allowing for even a very weak spatial inhomogeneity completely removes the threshold, trading the requirement upon the wave amplitude with a requisite upon the duration of the interaction between the wave and particle.

Relevant heating of the quiet solar corona by Alfvén waves: a result of adiabaticity breakdown.

Ion heating by Alfvén waves has been considered for long as the mechanism explaining why the solar corona has a temperature several orders of magnitude higher than the photosphere. Unfortunately, as the measured wave frequencies are much smaller than the ion cyclotron frequency, particles were expected to behave adiabatically, impeding a direct wave-particle energy transfer to take place, except through decorrelating stochastic mechanisms related to broadband wave spectra. This paper proposes a new paradigm for this mechanism by showing it is actually much simpler, more general, and very efficient.

Alfvénic propagation: a key to nonlocal effects in magnetized plasmas.

A long-standing puzzle in fusion research comes from experiments where a sudden peripheral electron temperature perturbation is accompanied by an almost simultaneous opposite change in central temperature, in a way incompatible with local transport models. This Letter shows that these experiments and similar ones are fairly well quantitatively reproduced, when induction effects are incorporated in the total plasma response, alongside standard local diffusive transport, as suggested in earlier work [Plasma Phys. Controlled Fusion 54, 124036 (2012).

Experimental-like helical self-organization in reversed-field pinch modeling.

We report the first nonlinear three-dimensional magnetohydrodynamic (MHD) numerical simulations of the reversed-field pinch (RFP) that exhibit a systematic repetition of quasisingle helicity states with the same dominant mode in between reconnection events. This distinctive feature of experimental self-organized helical RFP plasmas is reproduced in MHD simulations at low dissipation by allowing a helical modulation of the plasma magnetic boundary similar to the experimental one. Realistic mode amplitudes and magnetic topology are also found.