New Stanford Facility Squeezes High‐Energy Electron Beams

Accelerator physicists at the Final Focus Test Beam, a new facility at the Stanford Linear Accelerator Center, have managed to squeeze the vertical width of a high‐energy electron beam down to 75 nanometers. That’s an order of magnitude smaller than the focal spots of the 50‐GeV electron and positron beams of the five‐year‐old Stanford Linear Collider. And it’s almost small enough for the TeV beams envisioned for the next generation of electron‐positron colliders. (See the article by Jonathan Wurtele on page 33.) Linear colliders, in which collisions must all happen in a single pass, require much tighter focal spots than do storage rings, where the beams pass through each other again and again. But for beam energies above about 100 GeV, circulating charged particles as light as electrons radiate away so much energy that storage rings would be prohibitively expensive. A TeV electron‐positron collider will, perforce, be a pair of face‐to‐face linacs.