Date Available

1-28-2020

Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department/School/Program

Physics and Astronomy

First Advisor

Dr. Wolfgang Korsch

Abstract

The neutron electric dipole moment (nEDM) collaboration at the Spallation Neutron Source plans to use ultra-cold neutrons in superfluid helium to improve the nEDM limit by about two orders of magnitude. In this apparatus, neutrons are stored in poly(methyl methacrylate), PMMA, cells located in a strong, stable electric field. This electric field is produced by high voltage electrodes located outside of the neutron cells. Several sources generate charged particles inside the neutron cells. The electric field pulls these charges farther apart, attracting each to the oppositely charged electrode. As the charges build up on the cells walls, they create an increasing electric field in opposition to the field of the electrodes, reducing the strength and stability of the net field. The field fluctuations need to be kept below 1% in order to achieve the desired sensitivity, making it necessary to study this cell charging behavior, determine its effect on the experiment, and find ways to neutralize the charge.

A compact test setup was designed to study this effect using a scaled down cell and electrodes. Charged particles are generated by ionizing the helium with a 137Cs source and the electric field is monitored via the electro-optic Kerr effect. Linearly polarized light is passed through the helium. The Kerr effect then introduces an ellipticity to the polarization that is proportional to the square of the electric field. This effect is small compared to background noise; a triple modulation technique was used and adapted to measure the induced ellipticities. Liquid nitrogen was used to test the performance of the system. Having a Kerr constant that is over a factor of 100 larger than the helium Kerr constant, it is an ideal candidate for calibrating the polarimetry. Cell charging data was taken in liquid nitrogen as part of the system calibration and as a proof of principle. This document reports the results from the cell charging data taken in liquid nitrogen as well as the data taken in liquid helium.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.048

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