What is "plasma acceleration"

n. (context physics English) A method for accelerating electrically charged particles with a large-amplitude electron plasma wave.

Plasma acceleration is a technique for accelerating charged particles, such as electrons, positrons and ions, using an electric field associated with electron plasma wave or other high-gradient plasma structures (like shock and sheath fields). The plasma acceleration structures are created either using ultra-short laser pulses or energetic particle beams that are matched to the plasma parameters. These techniques offer a way to build high performance particle accelerators of much smaller size than conventional devices. The basic concepts of plasma acceleration and its possibilities were originally conceived by Toshiki Tajima and Prof. John M. Dawson of UCLA in 1979. Initial designs of experiment for "wakefield" were conceived at UCLA by the group of Prof. Chan Joshi. Current experimental devices show accelerating gradients several orders of magnitude better than current particle accelerators.

Plasma accelerators have immense promise for innovation of affordable and compact accelerators for various applications ranging from high energy physics to medical and industrial applications. Medical applications include betatron and free-electron light sources for diagnostics or radiation therapy and protons sources for hadron therapy. Plasma accelerators generally use wakefields generated by plasma density waves. However, plasma accelerators can operate in many different regimes depending upon the characteristics of the plasmas used.

For example, an experimental laser plasma accelerator at Lawrence Berkeley National Laboratory accelerates electrons to 1 GeV over about 3.3 cm (5.4x10 g), and one at the SLAC conventional accelerator (highest electron energy accelerator) requires 64 m to reach the same energy. Similarly, using plasmas an energy gain of more than 40 GeV was achieved using the SLAC SLC beam (42 GeV) in just 85 cm using a plasma wakefield accelerator (8.9x10 g). Once fully developed, the technology could replace many of the traditional RF accelerators currently found in particle colliders, hospitals and research facilities.

The Texas Petawatt laser facility at the University of Texas at Austin accelerated electrons to 2 GeV over about 2 cm (1.6x10 g). This record was broken (by more than 2x) in 2014 by the scientists at the BELLA (laser) Center at the Lawrence Berkeley National Laboratory, when they produced electron beams up to 4.25 GeV.

In late 2014, researchers from SLAC National Accelerator Laboratory using the Facility for Advanced Accelerator Experimental Tests (FACET) published proof of the viability of plasma acceleration technology. It was shown to be able to achieve 400 to 500 times higher energy transfer compared to a general linear accelerator design.

A proof-of-principle plasma wakefield accelerator experiment using a 400 GeV proton beam from the Super Proton Synchrotron is currently under construction at CERN. The experiment, named AWAKE, is scheduled for start-up at the end of 2016.