  We demonstrate laser-plasma acceleration of high charge electron beams to the
~10 MeV scale using ultrashort laser pulses with as little energy as 10 mJ.
This result is made possible by an extremely dense and thin hydrogen gas jet.
Total charge up to ~0.5 nC is measured for energies >1 MeV. Acceleration is
correlated to the presence of a relativistically self-focused laser filament
accompanied by an intense coherent broadband light flash, associated with
wavebreaking, which can radiate more than ~3% of the laser energy in a
sub-femtosecond bandwidth consistent with half-cycle optical emission. Our
results enable truly portable applications of laser-driven acceleration, such
as low dose radiography, ultrafast probing of matter, and isotope production.
