Electrode Design for a Cavallo High Voltage Multiplier in a Cryogenic nEDM Experiment

TL;DR

This paper presents the design of electrodes for a Cavallo high voltage multiplier used in cryogenic neutron EDM experiments, achieving high voltage gain with minimized breakdown risk.

Contribution

It introduces a finite element analysis-based electrode design that enables high voltage gain and low breakdown probability in cryogenic conditions.

Findings

Achieved a voltage gain of 18, reaching 650 kV.

Distributed electric fields of 116 kV/cm to prevent breakdown.

Designed electrodes suitable for cryogenic, high-voltage applications.

Abstract

The Cavallo multiplier [http://archive.org/details/b28771035_0003] is an electrostatic inductance machine that can generate low-noise high voltages electrically isolated from its voltage input, making it ideally suited for precision experiments. Its in-situ production makes it especially useful in cryogenic experiments, where the use of traditional feedthroughs is challenging due to thermal, electrical, magnetic, and physical size considerations. One such experiment is a cryogenic measurement of the neutron electric dipole moment (nEDM) [arXiv:1908.09937,arXiv:2512.14975], which requires several hundred kilovolts on a measurement cell electrode in 0.4 K liquid helium (LHe). A Cavallo multiplier can generate this voltage by stepping up a smaller input (e.g., 50 kV) from a feedthrough. We designed Cavallo electrodes using finite element analysis to provide high voltage gain and low probability of electrical breakdown in the experimental apparatus. The final geometry achieves a gain of 18, providing a target of 650 kV with peak electric fields of 116 kV/cm distributed over small areas to limit breakdown risk.