An electron beam can be refracted

An Electron Beam Can Be Refracted at the interface between a plasma and a gas, much as light is refracted at an air–water interface. A California-based research collaboration (University of Southern California, UCLA, and Stanford) used a beam from SLAC’s Final Focus Test Facility, consisting of 20 billion electrons at 28.5 GeV in a bunch that was about 0.7 mm long and 40 µm in radius. As the electron beam passed through a long, thin “tube” of plasma, it first repelled plasma electrons, leaving the sluggish ions behind to form a positively charged channel, which focused the remaining electrons. As the beam left the plasma at a grazing incidence, the ion channel became asymmetric and the exiting beam was deflected by up to a milliradian. The researchers also showed that, at sufficiently small incident angles, the beam underwent total internal reflection. Thus, they envision magnet-free particle-storage rings or plasma-based wires, although such “plasma waveguides” may require a laser to preform the ion channel. (P. Muggli et al. , Nature 411, 43, 2001 .)