An igniter laser pulse forms a "wire" of plasma in a plume of hydrogen gas; a heater pulse expands the wire to a plasma channel; the drive pulse accelerates bunches of electrons inside the channel to nearly uniform high energy. (The green cone represents associated terahertz radiation.)
Without a preformed channel (left) the drive laser pulse blows out after a few hundred micrometers, producing diffuse bunches of electrons with wide energy spread. A preformed channel through the plasma (right) confines the drive beam and produces bunches of electrons with nearly uniform high energy.
Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory have taken a giant step toward realizing the promise of laser wakefield acceleration, by guiding and controlling extremely intense laser beams over greater distances than ever before to produce high-quality, energetic electron beams.
For a quarter of a century physicists have been trying to push charged particles to high energies with devices called laser wakefield accelerators. In theory, particles accelerated by the electric fields of laser-driven waves of plasma could reach, in just a few score meters, the high energies attained by miles-long machines using conventional radio-frequency acceleration. Stanford’s linear accelerator, for example, is two miles long and can accelerate electrons to 50 GeV (50 billion electron volts). Laser wakefield technology offers the possibility of a compact, high-energy accelerator for probing the subatomic world, for studying new materials and new technologies, and for medical applications.
In plasmas, researchers have generated electric fields a thousand to ten thousand times greater than in conventional accelerators — but these large fields exist only over the short distance that a laser pulse remains intense; for tightly focused beams, that distance is typically only a few hundred micrometers (millionths of a meter). The resulting beams are of relatively poor quality, with particle energies so widespread that fewer than one percent have enough punch for scientific applications.
Paul Preuss | EurekAlert!
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