Checkout www.Plasmerg.com for the most recent progress in this area. If it's impossible, it looks like a lot of people are wasting money and resources. The US underwater naval research agency tested one of Papp's cylinders in the form of a cannon. The thing blew up! There were no expolosives and was checked and monitored by their researchers. Just a few cc's of noble gas mixture and the ignition chamber. The navy validated it...yet Papp(crazy, paranoid, secretive Papp) never released information on how to recreated the process to them.
Gas filled vacuum? I think they are saying the chambers are filled with gas. But after each detonation the gas cools and returns to a negative pressure.
