THe way to do this is to have a confining RF beam that keeps the gas isolated. There is a thing called cold plasma, but its not as damaging as one might want.
The first step in the process is to agitate the gas to get it to loose one of its outershell electrons, this generally can be done with vacuum UV, next step up the frequency progressively to remove lower electrons. This can be done with UV/Xrays. Finally to put pressure on the nucleus this can be done with Xrays (this gives the final bit of force required for a hydrogen-bomb). This gets the gas to move quite rapidly and in the confined space created by RF it will move in the direction of the momentum imparted by the Xrays.
I have to say, the xrays over great distance will probably be more damaging to the target than the plasma. In fact why waste your time, photon weapons achieve the same result, if you know the surface composition of the target, just pound the target with different wavelengths at its excitations frequencies, and dumb in a few X-rays, that has the effect of generating basically alpha and beta particles, but at much higher doses than a typical laboratory.