Surface discharges for soft x-ray preionization in light-ion-fusion accelerators

The authors investigate surface discharges as extreme ultraviolet (XUV) photon sources for preionizing anode surfaces of ion diodes in light-ion-fusion accelerators. Preionization is important both to control the diode impedance and to efficiently generate an ion beam. The surface discharges and their power feeds were constructed in a strip-line configuration to minimize overall system inductance. In some cases a 0.6-μF peaking capacitor was added to the circuit as close as possible to the surface discharge. These discharges radiated peak XUV powers of over 20 MW and total energies of over 5 J when driven by a low-energy (480 J) capacitor bank. These discharges were used to preionize the anode surface in an Applied-β diode on the Nereus accelerator (500 kV, 40 kA). Preionizing a cleaned LiF anode with 60 kW/cm/sup 2/ of XUV photons resulted in improved beam uniformity, flatter impedance profile, and a factor of 4 more ion beam energy coupled through the diode