Surface processing and discharge-conditioning of high voltage electrodes for the Ra EDM experiment

The Ra EDM experiment uses a pair of high voltage electrodes to search for the atomic electric dipole moment $^{225}$Ra. We use identical, plane-parallel with primary gradient surface 200 mm$^2$ generate reversible DC fields. Our statistical sensitivity is linearly proportional field strength in electrode gap. adapted decontamination and processing techniques from accelerator physics literature chemical polish clean suite newly fabricated large-grain niobium grade-2 titanium electrodes. Three pairs one were discharge-conditioned custom test station at strengths as $+52.5$ kV/mm $-51.5$ over gap sizes ranging 0.4 mm 2.5 mm. One was validated operate $\pm 20$ steady-state leakage current $\leq 25$ pA ($1\sigma$) polarity-averaged $98 \pm 19$ discharges per hour. These installed experimental apparatus, replacing copper pair, revalidated kV/mm. perform an 3.1 times larger than legacy are ultimately limited by maximum output our 30 kV bipolar power supply.