  Generation of attosecond bunches of energetic electrons offers significant
potential from ultrafast physics to novel radiation sources. However, it is
still a great challenge to stably produce such electron beams with lasers,
since the typical sub-femtosecond electron bunches from laser-plasma
interactions either carry low beam charge, or propagate for only several tens
of femtoseconds. Here we propose an all-optical scheme for generating dense
attosecond electron bunches via the interaction of an intense Laguerre-Gaussian
(LG) laser pulse with a nanofiber. The stable bunch train results from the
unique field structure of a circularly polarized LG laser pulse, enabling each
bunch to be phase-locked and accelerated forward with low divergence, high beam
charge and large beam-angular-momentum. This paves the way for wide
applications in various fields, e.g., ultrabrilliant attosecond x/$\gamma$-ray
emission.
