Delivering extreme voltages into vacuum loads is a defining challenge for next-generation facilities in high energy density physics and fusion research. A key limitation arises at the vacuum-insulator interface, where surface flashover occurs well below traditional breakdown limits. Field emission from the dielectric surface is widely suspected to seed the initial plasma responsible for anode-initiated flashover, yet quantitative data on its onset, magnitude, and spatial structure have remained limited. To address this gap, a novel electron diagnostic is used to obtain spatially resolved emission maps from insulator surfaces under pulsed excitation. Emission currents spanning from tens of nanoamps to hundreds of microamps are measured from dielectrics with a variety of surface preparations. These measurements supply new quantitative constraints for flashover modeling and represent a step toward reliable operation of pulsed power insulators in increasingly demanding environments.
Supported by the LDRD program at SNL. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.