  Configurations of a single semiflexible polymer is studied when it is pushed
into a nanochannel in the case where the polymer persistence length $l_p$ is
much longer than the channel diameter $D$, i.e. $l_p/D \gg 1$. Using numerical
simulations, we show that the polymer undergoes a sequence of recurring
structural transitions upon longitudinal compression, i.e. random deflection
along the channel, helix going around the channel wall, double-fold random
deflection, double-fold helix, etc. We find that the helix transition can be
understood as buckling of deflection segments, and the initial helix formation
takes place at very small compression with no appreciable weak compression
regime of the random deflection polymer.
