The radiation emitted from a duoplasmatron ion source has been investigated between 500 and 2000 Å. When the ion source is operated with hydrogen, the familiar hydrogen continuum is produced down to 1650 Å, followed by the many‐lined spectrum down to 900 Å, including the atomic Lyman alpha and beta lines at 1215.7 and 1025.7 Å, respectively. With argon the source emits a line spectrum down to 550 Å originating from excited neutral, singly, and doubly ionized argon atoms.