From Scientific American:
Power of plasma
Princeton University's fourth annual “Art of Science” exhibition features scientific imagery focused on the theme of energy. The $250 first prize for 2010 goes to “Xenon Plasma Accelerator” by Jerry Ross, a postdoctoral researcher at the Princeton Plasma Physics Laboratory. The photo shows a plume from a Hall-effect thruster, which uses magnetic and electric fields to ionize and accelerate propellant.