High Voltage Electrode Conditioning for use in the Measurement of the Permanent Electric Dipole Moment of Radium-225*

An electric dipole moment (EDM) is an observable indication of time reversal symmetry violation, new sources of which are needed to explain the dominance of matter over antimatter in the universe. Due to its pear-shaped nucleus, the ²²⁵Ra atom has an increased sensitivity to this violation. To search for an EDM, we measure the difference in the clock rate under reversal of the electric field with respect to the magnetic field. A uniform and stable electric field is applied to an ensemble of ²²⁵Ra atoms in order to measure its EDM. Our immediate goal is to improve the electric field by a factor of three, and by more than a factor of 10 in the long term. We do this by conditioning round Nb electrodes to remove microscopic imperfections. Our progress is measured by monitoring the electrodes for discharges and a steady state leakage current as we increase the potential difference. We started with electric fields of ±10 kV/mm, and have been able to validate ±20 kV/mm, with a long term goal of ±100 kV/mm, as produced in previous experiments.