AD warmly acknowledges support from the Department for Employment and Learning (DEL) Northern Ireland via a postgraduate scholarship at Queen's University Belfast. The work of IK and NSS was supported via a Science and Innovation (S & I) grant to the Centre for Plasma Physics (Queen's University Belfast) by the UK Engineering and Physical Sciences Research Council (EPSRC grant No. EP/D06337X/1). The work of MAH is supported in part by the National Research Foundation of South Africa (NRF). Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and therefore the NRF does not accept any liability in regard thereto.