High Electric Field Studies in Liquid Helium for the nEDM@SNS Experiment

The nEDM@SNS collaboration is constructing an experiment to search for a neutron electric dipole moment (EDM) using ultracold neutrons (UCN) stored in superfluid liquid helium. This experiment will be run at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. The nEDM@SNS experiment requires a very strong and stable electric field in the superfluid helium neutron storage region since the EDM measurement sensitivity depends linearly on field strength. The phenomenon of electric breakdown in liquid helium is poorly understood, which motivates a large R&D effort. An apparatus called the Half Scale High Voltage system (HSHV) has been constructed at Los Alamos National Laboratory to study electrical breakdown in superfluid liquid helium at pressures between the saturated vapor pressure and 1 atm. This experiment will use larger electrodes, up to half the size planned for the nEDM@SNS measurement, complementing results from previous studies. This talk will discuss the engineering and scientific challenges of the HSHV system and show the recent results from the first high voltage studies.