Thin current sheets: from the work of Ginzburg and Syrovatskii to the present day

We outline the history and development of the theory of thin current sheets in a collisionless space plasma from the early ideas of V L Ginzburg and S I Syrovatskii to the present day. We review the key achievements of the quasi-adiabatic theory, which provided insight into the fine structure of thin current sheets and enabled a comparison with experiment. This comparison showed the quasi-adiabatic approach to be more effective than the classical MHD approximation. With the development of the quasi-adiabatic theory in the last two decades, the existence of a number of new thin current sheet features, such as multi-scaling, metastability, and embedding, has been predicted and subsequently confirmed in situ; the role of individual particle populations in the formation of the current sheet fine structure has also been investigated. The role of nonadiabatic effects in accelerating plasma beamlets interacting with current sheets is examined. Asymmetry mechanisms in thin current sheets in the presence of a magnetic shear component are described. A study is carried out of current sheet self-organization processes leading to the formation of a shear magnetic component consistent with currents flowing in the plasma. It is demonstrated that the ongoing development of the theory of thin current structures is a logical continuation of Syrovatskii's and Ginzburg's ideas on cosmic rays and reconnected current sheets in the solar corona.