i'm thinking a simple particle beam driven by a diamond aperture with a massive EM focusing point at the end of the hilt that redirects and spins the beam energy cross.rotationally down and around the core beam back towards the emitter and into a collector/recirculator aperture would be somewhat feasible. the energy requirements would be less, the EM fields are containable, and the particles used would give it color based on the vibration patterns of the EM fields twisting them into their designated path. the down side though, is that you would need a steady supply of particles (oh wait... air is made of particles) as well as nano-tech energy cells, which we're not too far from making. after that, it's just perfecting the EM fields and not having any electronics on you.