  We present experiments and numerical simulations which demonstrate that
fully-ionized, low-density plasma channels could be formed by hydrodynamic
expansion of plasma columns produced by optical field ionization (OFI).
Simulations of the hydrodynamic expansion of plasma columns formed in hydrogen
by an axicon lens show the generation of \unit[200]{mm} long plasma channels
with axial densities of order $n_e(0) = 1 \times 10^{17} cm^{-3}$ and
lowest-order modes of spot size $W_M \approx 40 \mu m$. These simulations show
that the laser energy required to generate the channels is modest: of order 1
mJ per centimetre of channel. The simulations are confirmed by experiments with
a spherical lens which show the formation of short plasma channels with $1.5
\times 10^{17}cm^{-3} \lesssim n_e(0) \lesssim 1 \times 10^{18} cm^{-3}$ and
$61 \mu m \gtrsim W_M \gtrsim 33 \mu m$. Low-density plasma channels of this
type would appear to be well-suited as multi-GeV laser-plasma accelerator
stages capable of long-term operation at high pulse repetition rates.
