CryoEDM

Abstract: This document is a copy of the original 2003 proposal for the construction grant for the CryoEDM Experiment at ILL, Grenoble. It is here made publicly available as a technical reference source for interested parties. It does not necessarily represent the final configuration of the experiment. Items pertaining to costs, personnel etc. have been removed.

Abstract: Precision magnetometry is an essential component of any neutron electric dipole moment experiment in order to correct shifts in the neutron precession frequency due to changes in the magnetic field. We have developed a magnetometry system using 12 SQUID sensors, designed to operate in 0.5 K superfluid helium. The pick-up loops located near the neutron cell are connected to the SQUID sensors by ~2 m twisted wire pairs. The SQUID readout cables are run via an intermediate stage at 4.2 K. The system has been installed and tested in the cryoEDM apparatus at the ILL, Grenoble, and used to characterise the magnetic environment. Further tests in a suitable low noise environment confirm it meets our requirements.

Abstract: We have developed multichannel SQUID systems for two particle physics experiments: a 66-channel system for detector readout in the CRESST dark matter search, and a 12-channel magnetometry system for the CryoEDM neutron electric dipole moment experiment. These different applications have different requirements, for example in the CRESST system it is important to minimise crosstalk, while the CryoEDM system must be shielded from magnetic noise. Future experiments such as the EURECA dark matter project may require systems with a much higher number of channels.

Abstract: This thesis presents a new Monte-Carlo based simulation of the physics of ultra-cold neutrons (UCN) in complex geometries and its application to the CryoEDM experiment. It includes a detailed description of the design and performance of this simulation along with its use in a project to study the magnetic depolarisation time of UCN within the apparatus due to magnetic impurities in the measurement cell, which is a crucial parameter in the sensitivity of a neutron electricdipole-moment (nEDM) experiment. This project involved experimental measurements taken at the Institut Laue Langevin (ILL) of the magnetic environment inside of CryoEDM's measurement cell, along with the magnetic field produced by a set of 19 coils around the cell used to optimise the field in particular locations. It also involved the development of a separate computer program to find the required current setting of these coils so as to minimise the field gradient across the measurement cell, and then use of the simulation to study the effect of these coil configurations on the magnetic depolarisation time.