As I wrote in the Ghostbusters.net forum, it’s impossible to build a backpack-sized cyclotron, but there is a real device that comes very close to the operating principle of a proton pack: the ion ray gun. It’s basically a portable pulsed high voltage power supply where the signals from two 555 timers are amplified through a transistor, two step-up transformers and a Cockcroft-Walton multiplier. This creates enough voltage to ionize the air near the discharge terminal; the positive ions so obtained are repelled by the terminal because it has a positive charge too.
I built an ion ray gun from the plans on Robert Iannini’s book Electronic Gadgets for the Evil Genius and made a video where I show some of the interesting effects that can be obtained with it:
The video also shows what is my absolutely favorite part from any episode of The Real Ghostbusters, because it’s the one that comes the closest to describing an ion ray gun. And after that clip, I repeat the experiment it showed! (of course, without any ghost 
)
