Electrohydrodynamic lithium ion-source experiments on PBFA [Particle Beam Fusion Accelerator] 2

We are developing anodes to test the electrohydrodynamic (EHD) instability as a means of producing an intense lithium beam on Sandia's Particle Beam Fusion Accelerator II. In a strong electric field (∼10 MV/cm) a molten lithium or lithium nitrate surface is predicted to become EHD unstable and deform into a dense array of cusps with sub-micron spacing. Ions field-evaporated from the cusp tips from the ion beam. We have dealt with a number of problems in fielding these liquid sources in PFBA II. The vertical liquid anode surface required has been formed by suspending the molten anode material in a porous metal frit. In order to attain the high electric fields required to turn on the EHD source, 5-Tesla B-fields must be impressed in the A-K gap of the Applied-B ion Diode. Unless the amount of flux passing through the anode surface is carefully minimized, eddy currents induced in the anode cause the ejection of molten lithium from the anode surface. Applying the 5-Tesla B-fields on the diode has required peak currents in the diode B-field coils of 70--100kA. Rapid corrosion of molten lithium occurs even in the 5 x 10-5 Torr diode vacuum. Recent developments include a new diode design which has allowed us to reach a uniform 5-Tesla B-field on the anode surface, fast heating of the anode, which melts the lithium and allows it to wick up into the anode frit just before the accelerator shot, and development of reflectance-based monitors of molten anode surface quality. Results of recent accelerator shots will be discussed. 2 refs., 12 figs