An ion optical system suitable for extracting dense ion beams from gas discharges is described. A study of the beam forming characteristics of the system was performed by using an automatic trajectory tracer with space‐charge simulation. Experimental measurements show that the extraction system operates satisfactorily over a wide range of current densities; total mercury‐ion beam currents in excess of 1 A have been achieved. An empirical method of estimating perveance as a function of geometry, based on electrolytic tank measurements, is in agreement with experimental results.