For the High Current Beam Transport Experiment (HCX) at Lawrence Berkeley National Laboratory, an injector is required to deliver up to 1.8 MV of 0.6 A K⁺ beam with an emittance of ≈1 π-mm-mrad. We have successfully operated a 10-cm-diameter surface ionization source together with an electrostatic quadrupole (ESQ) accelerator to meet these requirements. The pulse length is ≈4 μs, firing at once every 10–15 s. By optimizing the extraction diode and the ESQ voltages, we have obtained an output beam with good current density uniformity, except for a small increase near the beam edge. Characterization of the beam emerging from the injector included measurements of the intensity profile, beam imaging, and transverse phase space. These data along with comparison to computer simulations provide the knowledge base for designing and understanding future HCX experiments.