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