On Sunday, November 29, 2015 at 3:57:50 PM UTC-8, Christopher Tidy wrote:

Just now I had the idea of using particles conveyed by a gas. Powder fire extinguisher style. I need to think that one through. Metal particles would be like sandblasting and would probably destroy the machine, but some other powder might work.

Yeah, like ice pellets. The charge transfer between small ice pellets (caught in an updraft)
and larger ice pellets (too heavy to move upward) is (the, a?) cause of lightning.
There's a charge-segregation at the surface of ice (which is why ice is slippery),
that lies at the heart of the phenomenon.