High temperature superconducting combined function magnet for carbon-ion radiotherapy
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Date
31/07/2021Author
Baird, Yvonne Turid Eiking
Metadata
Abstract
With an increase in cancer cases seen year on year, developing and improving
treatment forms becomes increasingly important. Treatment of cancerous tumours
using carbon-ion radiotherapy has shown favourable results compared to conventional
treatment methods. However, enabling this treatment form to become more widely
available on a world-wise basis remains a key challenge, due to the facility size and
cost. In recent years, material and manufacturing developments of superconductors
has improved the performance of high temperature superconductors (HTS) while their
price has come down. This has allowed more compact accelerator and gantry magnets
to be designed. The inherent characteristics of second generation (2G) HTS enable a
drastic increase in the current density and magnetic field generated, compared to
normal conductors and low temperature superconductors (LTS). For future
superconducting applications, HTS has therefore been recognised as the solution. This
thesis aims to address the issue of magnet size and associated costs, by employing 2G
HTS in the design of a compact magnet through a layer-by-layer design algorithm.
This new design resulted in a reduction of 26.3% of superconducting material used
compared to other known designs, thus a cost saving of $115835.
The thesis begins by presenting a brief overview of particle therapy, and the
application of superconducting technology in these facilities, followed by a concise
review of superconductors. The important steps and design considerations to design a
magnet are then presented. This includes cross-section and coil end design, yoke
design, field quality, and field computation modelling.
The thesis goes on to present the designed HTS combined function magnet,
designed for use in carbon-ion radiotherapy. The six-layer combined function magnet
realises both bending and focusing/defocusing components in each layer, thus utilising
space and materials effectively. This resulted in a precise and compact magnet, which
uses considerably less HTS material compared to other designs. A further size
reduction was achieved by the yoke design and optimisation which followed, which
utilised COMSOL Multiphysics and Magnet Infolytica to simulate the magnet and iron
yoke, using the finite element method (FEM).
FEM is implemented for both stationery and time-dependent simulations. An
anisotropic homogeneous-medium bulk approximation is adopted with a power law E
– J relationship to model the combined function magnet during magnet ramp. This
allowed a comprehensive profile of the HTS tape blocks to be obtained, in addition to
several important issues such as magnetisation and critical current of the
superconducting coils to be addressed.