I admit the system is unorthodox and may not work. Can we divide it into components that collaborators could research and advise on?
Railgun systems have been built with big power supplies to handle heavy payloads. The amount of fuel for a dpf would be a light load and could use a much smaller railgun machine. There is a big difference between the mass of fuel and metal contaminants. That could reduce the size of the separation magnets. If preionization of the dpf chamber is still needed it would be handled in a different way. The vaporization of the dpf electrodes is a major unknown because the plasma sheath may not outrun the heavy electrode ions. The operators of plasma railguns could comment on how much metal is present in their plasmas.