  The distant projection of high peak and average power laser beams in the
atmosphere is a longstanding goal with a wide range of applications. Our early
proof-of-principle experiments [Phys. Rev. X 4, 011027 (2014)] presented one
solution to this problem, employing the energy deposition of femtosecond
filaments in air to sculpt millisecond lifetime sub-meter length air
waveguides. Here, we demonstrate air waveguiding at the 50 meter scale, 60X
longer, making many practical applications now possible. We employ a new method
for filament energy deposition: multi-filamentation of Laguerre-Gaussian LG01
"donut" modes. We first investigate the detailed physics of this scheme over a
shorter 8 m in-lab propagation range corresponding to ~13 Rayleigh lengths of
the guided pulse. We then use these results to demonstrate optical guiding over
~45 m in the hallway adjacent to the lab, corresponding to ~70 Rayleigh
lengths. Injection of a continuous wave probe beam into these waveguides
demonstrates very long lifetimes of tens of milliseconds.
