Plasma turbulence is believed to be responsible for the fact that the solar wind – the supersonic expansion of the Sun’s corona – retains a high temperature throughout the heliosphere, even when it is expected to cool due to expansion. The solar wind may be heated by releasing magnetic energy to accelerate particles at thin magnetic discontinuities, or current sheets. In some models these current sheets are formed at the same time as the solar wind leaves the Sun, or they may form spontaneously as part of the turbulence seen in the solar wind.
Using DiRAC we have carried out self-consistent, particle kinetic plasma simulations of the evolution of thin current sheets in a three-dimensional geometry. We find that there are two important instabilities which control energy release. The ion tearing instability releases energy via magnetic reconnection, and the drift-kink instability which, as it name implies, produces a rippled current. The drift-kink instability can reduce the rate of energy release, and lead to thicker current sheets which are less liable to reconnect due to the tearing instability. The competition between these two instabilities can only be studied with three-dimensional simulations, and these require large memory and processor numbers which would not be possible without DiRAC resources.
Our results indicate that the importance of thin current sheets to solar wind heating might be less than predicted by two-dimensional simulations which only capture the ion tearing instability. Energy release at current sheets could be important if they are actively produced at a high enough rate by large scale turbulence. We have also created virtual spacecraft data which can be used to test our simulations against actual data from spacecraft.