A hydrogen arc has been developed which produces a low‐density plasma column. The electrodes of the arc discharge are geometrically arranged such that the plasma drifts through a hole in the arc anode along a flux tube of the confining magnetic field.A differentially‐pumped vacuum system was constructed which achieved a base pressure of 2.5×10−10Torr in the inner liner region while at liquid‐nitrogen temperature. A density of about 1010particles cm−3can be achieved in the plasma column contained in the inner liner region, down field from the arc chamber, with a gas flow of 2 cm3min−1into the arc chamber. At this flow, the pressure in the inner liner rises to 3×10−9Torr. The ion‐to‐neutral density ratio under these conditions is about 30 to 1 in the inner liner region.