XUV Preionization Effects in High Power Magnetically Insulated Diodes

Abstract : Electrode surface desorption and photoionization by an intense XUV pulse has been shown to dramatically Improve a vacuum diode impedance history. The 6- Terawatt Applied-B ion diode experiment on PBFA I is limited by a delay in both diode and ion current initiation. The insulation magnetic field impedes electron crossings which are believed to aid the ion source initiation. The diode is therefore initially a severe overmatch to the accelerator 40-nsec, 2.2-MV, 0.5-ohm pulse. The diode current increases during the pulse, leading to a rapidly falling impedance history. 2 The application of an intense (30 to 50-kW/cm) XUV flux from an array of sixteen 60-kA spark sources is found to cause immediate diode current flow, resulting in both a greatly improved impedance history and the prompt initiation of an intense higher power ion beam.