Supermite vacuum interface design

A new water-plastic-vacuum interface has been designed for Sandia Laboratory's Supermite (2.8 MV, 2.2 ohm) accelerator. This design was based on the PBFA I vacuum interface. Electrostatic field plots show that in positive polarity the water feed to the PBFA I interface will fail at 2 MV on Supermite. This is confirmed by positive polarity experiments and field plots using the PBFA I style vacuum interface at the Naval Research Labs. Modifications to the water section geometry to increase the water breakdown strength in positive polarity result in equivalent electric field grading at the plastic-vacuum interface but allow positive polarity operation at voltages up to 3.1 MV. This is accomplished by incorporating a dielectric field shaper which significantly improves the electric field grading across the insulator