Application of permanent magnet assemblies to RF- and Arc-driven discharges*

We are reporting progress in the development of solenoid-like magnetic field configurations using assemblies of permanent magnet. It was demonstrated that ring assemblies of axially magnetized Nd cylinders create ~0.5T uniform fields in the bores [1]. However, the high field domain it is terminated by magnetic cusps at the exits. We propose a few configurations that can mitigate these singularities to form an open magnetic field topology. The first configuration is an umbrella-like expandable structure of ~30cm long rod magnets, producing B~0.1T [2].  It was used to facilitate continuous rf-driven helicon Ar/N2 discharges [3] and exhaust plasma axially. The second assembly is a reconfigurable chain of 3D-printed magnet holders that has several degrees of freedom. Six chains are anchored together to form a magnetic mini-nozzle with B~0.2T at the high end. The enhancing effect of added ferromagnetic wedges is described as well. A short nozzle is used to facilitate pulsed arc-driven discharge and direct the metal plasma flow.

[1] A.Hyde, A.Taylor, O.Batishchev, IEEE Trans. Plasma Sci. 46(2), 2018, doi: 10.1109/TPS.2018.2790362

[2] A.Hyde, Doctoral Thesis, 2018, doi: 10.17760/D20324054

[3] A.Hyde, O.Batishchev, Phys. Plasmas 28, 073504 (2021); https://doi.org/10.1063/5.0040344