We present the design, construction, measurement, and troubleshooting of a prototype hybrid Halbach quadrupole magnet. This magnet was significantly under-strength due to local demagnetization in the permanent magnet material. We discuss how this effect was uncovered, how it was verified by performing Hall probe measurements of the individual magnet blocks, and how the effect was reconstructed in simulations.

The production of high current beams of multiply charged ions has many applications, such as accelerator-based medical isotope production and optimisation of the atomic to molecular ion ratio in high-current proton sources relevant for major accelerator facilities. Microwave discharge ion sources are one option for production of ion beams. These sources require a system to generate a magnetic field which is resonant with a coupled microwave input to generate the plasma. In simple designs using solenoid magnet coils, the resonant field surface that is produced is open ended and leads to poor plasma confinement and these ion sources produce only singly charged ions. Other designs require complex magnet arrays which combine solenoid and multipole fields to form a closed resonant surface in order to achieve multiple charge states, but at the expense of lower beam currents. We present here the design of a novel method for generating a closed resonant field surface from a simplified permanent magnet array without a solenoid. The magnet system consists of an array of permanent magnets rods and steel pole pieces whose arrangement can produce the closed surface without the requirements for any electrical power. A mechanical tuning system allows adjustment of the shape and size of the closed resonant surface. A prototype proof of principle device has been designed for application to a 2.45 GHz microwave source. The prototype will be built to measure the magnetic field distribution created by this magnetic array and to test the generation and tuning of the closed resonant field surface. Future work will aim to test this magnet device on an operational plasma chamber to measure how the plasma density can be adjusted through tuning of the closed resonant field surface.

Boundary Element Methods (BEMs) can be applied to determine the value of the magnetic field at any point within a domain if the magnetic field components are measured on the surface of the domain. For large magnetic volumes, BEMs provide an attractive alternative to fine three-dimensional Hall probe scans for determining the local shape of the field as the fields can be evaluated inside the volume with an arbitrary position and with a reduced measurement time. BEMs have been applied to the field data measured on the boundary of three-dimensional Hall probe scans for two example magnets, which have been measured at STFC Daresbury Laboratory, UK. The fields reconstructed using BEMs are compared to the fields directly measured during the Hall probe scans. The reconstructed fields can be calculated to within 1 mT rms of the directly measured fields. For the transverse field components greater than 1 mT, the fields can be reconstructed to within 5% rms of the directly measured fields.