m=0,±1 low frequency fast Alfven modes of a plasma column loaded in a sheath helix

The dispersion relation for a cold, collisionless plasma column loaded in a sheath helix is derived. This is then solved numerically for the m=0, +or-1 fast Alfven waves for different plasma radii and helic parameters; the frequency range is below the ion cyclotron frequency. The results are compared with those of the plasma-waveguide system. There is no m=0 cut-off and instead there are two (m=0) waves which propagate down to low frequencies. While the m=+1 mode retains its general behaviour, the m=-1 mode is altered significantly. Relevance of these results to the coupling of Alfven waves with helices is discussed.