A small, low-power, lightweight arc plasma generator is described which is highly efficient electrically. The design, which utilises a small permanent magnet, has enabled electrode erosion problems to be solved, and the generator can be tuned to operate continuously on a variety of gaseous feedstocks (for example N2, CH4, H2) with high stability and without the necessity for any noble monatomic gas additives. The fine tuning also enables the generator setting to be optimised selectively for particular atomic states, while the interchangeable anode construction has allowed species generated within the arc to be expanded into a variety of pressures with low recombination losses. These facilities are of potential use both in academic studies (lasers, molecular beams etc.) and in practical combustion situations.