Some recent studies of particle acceleration in tokamak plasmas will be presented, and possible implications for fast particle production in solar flares will be discussed. Microwave and soft X-ray bursts observed during edge localised modes (ELMs) in the Mega Amp Spherical Tokamak (MAST) and in some other tokamak experiments can be attributed to energetic electrons accelerated by parallel electric fields associated with the ELMs [1]. The very large numbers of electrons known to be accelerated in solar flares must also arise from parallel electric fields, and indeed links have been drawn previously at the fluid level between ELMs and flares [2], but the demonstration of energetic electron production during ELMs suggests that the links extend to kinetic effects, hitherto neglected in ELM models. Energetic particle studies in solar flares have focussed largely on electrons rather than ions, since bremsstrahlung from deka-keV electrons provides the best available explanation of hard X-ray emission (one of the primary flare diagnostics). However the available solar flare data do not preclude the presence of large numbers of sub-MeV fast ions, and in this context it is noteworthy that ions (but not, so far, electrons) have been observed to be accelerated during reconnection resulting from merging-compression startup of plasmas in MAST.

Work supported by RCUK and Euratom.

[1] S.J. Freethy, K.G. McClements, S.C. Chapman, R.O. Dendy, W.N. Lai, S.J.P. Pamela, V.F. Shevchenko, R.G.L. Vann, Phys. Rev. Lett. 114, 125004 (2015)
[2] S.C. Cowley, H. Wilson, O. Hurricane, B. Fong, Plasma Phys. Control. Fusion 45, A31 (2003)