An aluminum plasma is produced by an anodic vacuum arc (25 A, 17 V) with a consumable anode. The plasma expands from the anode to the walls and is investigated by Langmuir probes, a quadrupole mass spectrometer, a retarding field ion energy analyzer, and a quartz‐crystal oscillator for mass flow detection. The electron density ranges within 2×1015–3×1017m−3and the electron temperature within 0.4–0.9 eV. At a target, ion fluxes of 1.5×1019–8×1020m−2 s−1and total particle fluxes of 3×1020–4×1021m−2 s−1are measured. The ions are accelerated in the expanding plasma towards the target and gain a few eV. By a simple collisionless transport model of the expanding plasma, the plasma potential and floating potential are calculated and compared with experimental data.