Confining arc plasmas with alternating magnetic fields

Plasma arcs have many uses in welding, machining, and materials processing. For these applications, it is essential that the arc is focused as narrowly as possible to produce the best quality welds. Most plasma arcs have low energy densities, resulting in broad welding seams and narrow welding depths. Existing methods to focus plasma arcs primarily rely on steady-state magnetic or mechanical confinement.

Wang et al. simulated a dynamic solution to plasma arc confinement using an alternating magnetic field to control the arc. Their solution results in higher current density than comparable steady-state solutions.

“In our research, the arc is pinched through continuous dynamic transitions between shrinking and expansion, and the subsequent confinement of arc plasmas is even more effective than under a constant magnetic field that has an equal field intensity,” said author Xiaoliang Wang.

A high frequency alternating magnetic field caused the plasma arc to oscillate between shrinking and expanding, trapping it in a narrower space. This reaction results from an interplay with the plasma’s inertia of motion, and the model suggests this dynamic confinement solution could be applied generally to most plasma arcs.

The researchers hope to refine their model to further confine arc plasmas.

“The next step of our work is to design and optimize proper spatiotemporal configurations of external magnetic or electric fields to better confine arc plasmas,” said Wang. “We expect this exploration can bring us exciting research results, which can have benefits for practical applications.”

Source: “Pinching arc plasmas by high-frequency alternating longitudinal magnetic field,” by Xiaoliang Wang, Andrew Harrison, Yunlong Chang, and Jian Liu, Physics of Plasmas (2022). The article can be accessed at https://doi.org/10.1063/5.0083796 .