A new Monte-Carlo based simulation for the CryoEDM experiment

Doctoral thesis English OPEN
Raso-Barnett, Matthew (2015)
  • Subject: QC0770

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\ud 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.
  • References (4)

    2 Neutron Electric Dipole Moment and the CryoEDM Experiment 10 2.1 The Neutron EDM . . . . . . . . . . . . . . . . . . . . . 10 2.2 Constraining the Neutron EDM Experimentally . . . . . 11 2.3 The Interactions of Ultra Cold Neutrons . . . . . . . . . 13 2.3.1 The Strong Interaction . . . . . . . . . . . . . . . . 13 2.3.1.1 Scattering from a Single Nucleus . . . . . . 13 2.3.1.2 The Fermi Potential: Scattering from a Collection of Nuclei . . . . . . . . . . . . . . . . 14 2.3.1.3 Total Re ection of Neutrons from Material Walls . . . . . . . . . . . . . . . . . . . . . . 16 2.3.1.4 Loss of UCN on re ection . . . . . . . . . . 19 2.3.2 Neutron Beta Decay; The Weak Interaction . . . . 25 2.3.3 The Gravitational Interaction . . . . . . . . . . . . 25 2.3.4 Magnetic Dipole Moment . . . . . . . . . . . . . . 26 2.4 Principles of the Experiment . . . . . . . . . . . . . . . . 27 2.4.1 Ramsey Method of Separated Oscillating Magnetic Fields . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.5 CryoEDM Overview . . . . . . . . . . . . . . . . . . . . 31

    3 The Design of the Simulation 34 3.1 Design Overview . . . . . . . . . . . . . . . . . . . . . . 34 3.2 Particle Model . . . . . . . . . . . . . . . . . . . . . . . . 35 3.2.1 Particle Attributes . . . . . . . . . . . . . . . . . . 36 [1] N. F. Ramsey, \Electric-dipole moments of elementary particles," Reports on Progress in Physics, vol. 45, no. 1, p. 95, 1982.

    tors and Associated Equipment, vol. 337, no. 2-3, pp. 504{511, 1994.

    [17] N. F. Ramsey, \Feasibility of a 3He magnetometer for neutron electric dipole moment experiments," Acta Physica Hungarica, vol. 55, no. 1-4, pp. 117{126, 1984.

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