Experimental Techniques for Magnetic Sensing and Control of Metal Vapor Plasmas

Since the 1940s, high temperature metal vapor plasmas have been used to refine specialty alloys under
vacuum to provide chemical and structural homogenization. Vacuum arc remelting has benefitted from
controls that interact with plasma including axial or transverse externally applied magnetic fields.
However, it was not until the early 2000s that the instabilities and dynamics of the distribution of plasma
throughout remelting furnaces were connected in a causal relationship with the micro- and macrostructural quality of the ingot product through defects, e.g., chemical segregation, inclusions, or voids.
That discovery ignited the last 20 years of development of sensing, control, and data analysis
methodologies based on magnetic flux tomography. Today, arrays of hundreds of synchronized magnetic
sensors are used in combination with externally applied magnetic fields to control the plasma and
optimize the process for metal quality and yield while ensuring safety in operations. This work provides
an informative review of the experimental techniques for magnetic sensing and control that have been
developed for the metal vapor plasma processing industry.