Peculiarities in the ionic tail of Comet Ikeya-Seki (1965 f)

Direct photographs of Comet Ikeya-Seki obtained on four consecutive days from October 29 to November 1, 1965, are used for an analysis of the multiple helical structures in the ionised tail. The formation of these structures is explained on the basis of plasma instabilities excited in the tail containing twisted magnetic fields. The growth rate of the modes excited at the mode rational surface agrees well with the observed results. This model also accounts for the presence of harmonic structures seen in the tail of the comet.