I considered that, but pinch cannot reverse the expansion of alike charges
unless they are in a net neutral volume, right? The pinch effect might
squeeze the current in a neutral conductor where there are equal - and +
charges, but for a charged particle stream, e.g. an electron beam, it
would just slow the outward expansion. When charged air flows from a
needle, can the pinch effect squeeze it into a filament, or would the air
stream act more like an electron beam?