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

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 1014; p. 165738
• Main Authors: Ready, Roy A., Arrowsmith-Kron, Gordon, Bailey, Kevin G., Battaglia, Dominic, Bishof, Michael, Coulter, Daniel, Dietrich, Matthew R., Fang, Ruoyu, Hanley, Brian, Huneau, Jake, Kennedy, Sean, Lalain, Peyton, Loseth, Benjamin, McGee, Kellen, Mueller, Peter, O’Connor, Thomas P., O’Kronley, Jordan, Powers, Adam, Rabga, Tenzin, Sanchez, Andrew, Schalk, Eli, Waldo, Dale, Wescott, Jacob, Singh, Jaideep T.
• Format: Journal Article
• Language: English
• Published: United States Elsevier B.V 21.10.2021; Elsevier
• Subjects: Atomic electric dipole moment; High voltage electrode conditioning; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; Large-grain niobium; Leakage current; Magnetic Johnson noise; Radium-225; Radium-225; Leakage current; High voltage electrode conditioning; Atomic electric dipole moment; Magnetic Johnson noise; Large-grain niobium
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2021.165738

The Ra EDM experiment uses a pair of high voltage electrodes to search for the atomic electric dipole moment of 225Ra. We use identical, plane–parallel electrodes with a primary high gradient surface of 200 mm2 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 ±20kV/mm with steady-state leakage current ≤25 pA (1σ) and a polarity-averaged 98±19 discharges per hour. These electrodes were installed in the Ra EDM experimental apparatus, replacing a copper electrode pair, and were revalidated to ±20kV/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.