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Magnetic field design for polarised neutrons in European Spallation Neutron Source instruments

Monzani, Andrea LU (2021) FYSK02 20211
Nuclear physics
Department of Physics
Abstract
The goal of this project is the design of the magnetic field of the neutron analyser for the European Spallation Source instrument DREAM (Diffraction Resolved by Energy and Angle Measurements). This instrument is a neutron diffractometer and its purpose is the determination of the magnetic and chemical structure of materials. Simulations have been performed over the span of a semester using the Finite Element Method (FEM) in a software called COMSOL Multiphysics. Three different setups, with different guide fields, have been investigated and compared in order to achieve the best results. This has required to study how to produce highly uniform magnetic fields with coils. The initial setup, where the guide was composed by four rectangular... (More)
The goal of this project is the design of the magnetic field of the neutron analyser for the European Spallation Source instrument DREAM (Diffraction Resolved by Energy and Angle Measurements). This instrument is a neutron diffractometer and its purpose is the determination of the magnetic and chemical structure of materials. Simulations have been performed over the span of a semester using the Finite Element Method (FEM) in a software called COMSOL Multiphysics. Three different setups, with different guide fields, have been investigated and compared in order to achieve the best results. This has required to study how to produce highly uniform magnetic fields with coils. The initial setup, where the guide was composed by four rectangular coils, was found not to meet the required field characteristics concerning adiabaticity and uniformity. The second setup, which comprised also four compensation coils, fulfilled the specifications. However, a third setup based on a Halbach four-coil exceeded the required field characteristics and thus allows for potential imperfections in the manufacturing of the coils. As part of this work, different aspects of neutron physics have been investigated, including, neutron scattering, spin-filtering and spin-transport, which are the main physics principles behind DREAM. (Less)
Popular Abstract
European Spallation Source (ESS) is a world leading research facility and its main purpose is the production of neutrons. Someone might wonder what to do with all these neutrons. The answer is the following. Neutrons do have potentially a lot of useful applications. For example, if someone breaks their arm and needs to go to the hospital, their arms get scanned using X-rays. If the research that is being carried at ESS will succeed, then one day it might be possible to do it with neutrons instead. One advantage of that would be that neutrons can do a more precise imaging than X-rays. Another interesting aspect to consider is that X-ray can potentially damage a biological tissue, while neutrons cannot. This means that neutrons can allow us... (More)
European Spallation Source (ESS) is a world leading research facility and its main purpose is the production of neutrons. Someone might wonder what to do with all these neutrons. The answer is the following. Neutrons do have potentially a lot of useful applications. For example, if someone breaks their arm and needs to go to the hospital, their arms get scanned using X-rays. If the research that is being carried at ESS will succeed, then one day it might be possible to do it with neutrons instead. One advantage of that would be that neutrons can do a more precise imaging than X-rays. Another interesting aspect to consider is that X-ray can potentially damage a biological tissue, while neutrons cannot. This means that neutrons can allow us to carry out a much deeper study of how a medicine is perceived by the body for example.
The principle behind the imaging is neutron diffraction. In other words we shoot neutrons against a sample, then by looking at what happens to them we figure out information about the sample, like its magnetic or chemical structure. My work is being carried in a particular instrument called DREAM. This machine works the following way. Once neutrons arrive, they are going to be filtered first, otherwise they cannot give us any interesting information. Neutrons are like the salad that you buy in the supermarket: you have to wash it before you eat it. Then the neutrons will do diffraction as already explained and finally they will be analysed.
My project focuses on designing a Helium based analyser for the diffractometer DREAM instrument. This is made by essentially two components. First a tube in which the neutrons travel after they have hit the sample. Around this tube there is a magnetic field guide. Afterwards there is a coil structure containing a Helium gas that interacts with the neutrons. The main tasks I work on are the simulations and the design of the magnetic field. The simulations are being done with the help of the Finite Element Method, a numerical method used to approximate equations which are impossible to be solved exactly. My project involves also learning about this numerical method, which is a very powerful one. This is the same one that was used by Enrico Fermi and his team to design the first nuclear bomb. Also, it is often used in combination with artificial intelligence to do facial recognition. In order to use this method, the computations are being carried with a software called COMSOL Multiphysics. A simulation software that implements the Finite Element Method.
To sum up, my project involves designing a component of the ESS instrument DREAM. (Less)
Please use this url to cite or link to this publication:
author
Monzani, Andrea LU
supervisor
organization
course
FYSK02 20211
year
type
M2 - Bachelor Degree
subject
keywords
FEM, COMSOL, uniform magnetic field, neutron scattering, European Spallation Source, neutron adiabaticity, neutron spin filtering, neutron spin transport, 3He polarisation analyser, Halbach coils, tetracoil, instrument design, neutron diffractometer, nuclear physics, material science, physics simulation
language
English
id
9051105
date added to LUP
2021-06-08 19:22:48
date last changed
2021-06-08 19:22:48
@misc{9051105,
  abstract     = {{The goal of this project is the design of the magnetic field of the neutron analyser for the European Spallation Source instrument DREAM (Diffraction Resolved by Energy and Angle Measurements). This instrument is a neutron diffractometer and its purpose is the determination of the magnetic and chemical structure of materials. Simulations have been performed over the span of a semester using the Finite Element Method (FEM) in a software called COMSOL Multiphysics. Three different setups, with different guide fields, have been investigated and compared in order to achieve the best results. This has required to study how to produce highly uniform magnetic fields with coils. The initial setup, where the guide was composed by four rectangular coils, was found not to meet the required field characteristics concerning adiabaticity and uniformity. The second setup, which comprised also four compensation coils, fulfilled the specifications. However, a third setup based on a Halbach four-coil exceeded the required field characteristics and thus allows for potential imperfections in the manufacturing of the coils. As part of this work, different aspects of neutron physics have been investigated, including, neutron scattering, spin-filtering and spin-transport, which are the main physics principles behind DREAM.}},
  author       = {{Monzani, Andrea}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Magnetic field design for polarised neutrons in European Spallation Neutron Source instruments}},
  year         = {{2021}},
}