Precision plasma wakefield acceleration

In the search for phenomena beyond the standard model, particle physicists have sought ever larger and more powerful facilities for accelerating and colliding charged particles. Accelerators based on plasmas, which can sustain electric fields orders of magnitude larger than conventional accelerators, could one day be a smaller and cheaper alternative. (See the article by Chandrashekhar Joshi and Thomas Katsouleas, Physics Today, June 2003, page 47 .) But the precision engineering required to accelerate particles efficiently and uniformly has been a challenge. Now Chandrashekhar Joshi (at UCLA), Michael Litos, Mark Hogan (both at SLAC), and their colleagues have taken a leap forward. In their plasma wakefield accelerator, two bunches of 20-GeV electrons, accelerated by SLAC’s two-km linear accelerator, were injected into a 30-cm chamber of lithium plasma. The first, or “drive,” bunch pushed aside the plasma electrons to create a high-field region in which the trailing bunch could pick up energy. The figure shows a simulation of the process, with the beam density shown in orange, plasma-electron density in blue, and the electric field E_z as an orange curve. With SLAC’s purpose-built Facility for Advanced Accelerator Experimental Tests , the researchers could precisely place the trailing bunch in the 100-µm plasma wake to boost its energy by 1.6 GeV with an energy spread of just 2%. Their next goal is to daisy-chain plasma accelerators together so that a single trailing bunch can tap the energy of several drive bunches. (M. Litos et al., Nature 515, 92, 2014 .)