A pulsed cold cathode ion source, giving peak proton currents in excess of one milliampere and average currents up to 50 microamperes, is described. The source is based on the Penning discharge using axial extraction of the ions. Some discussion of the discharge mechanism and the role of the cathode material is included. Installation and operation of this source in the Berkeley 4‐mv Van de Graaff and its performance in that machine is discussed.

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