In a cascaded arc, the plasma is created by a direct current between cathodes and a grounded anode. Gas enters the cascaded arc at the cathode side, the plasma is created in the narrow source channel and then expands through the anode nozzle to a low pressure chamber. Due to the large pressure difference between the arc and the chamber, the expansion can be supersonic in which case a shockwave is formed.
Cascaded arcs are used for different applications such as deposition and surface treatment. Another application is the testing of materials for the ITER divertor. The cascaded arc plasma source Magnum-PSI at the FOM Institute DIFFER was constructed for this purpose.
In addition to other cascaded arc plasma sources, Magnum-PSI has a strong magnet surrounding the low pressure chamber to confine the plasma beam. The plasma creation in the source of Magnum-PSI and the first part of the expansion were studied using PLASIMO. Due to the strong magnetic field, the convective and diffusive motion of the species across and around the magnetic field lines become coupled due to the Lorentz force. Furthermore, the diffusion in the plasma becomes coupled to the bulk flow and the electrostatic potential due to the Lorentz force and the Hall current. These couplings have been takent into account in PLASIMO to obtain a self-consistent description of the plasma. Results of the simulations have led to fundamental understanding of magnetized expanding plasmas. For example, new insight in the spatial distribution of the electric field and shockwaves in magnetized plasmas was obtained.