SIDEBARS:Table Top Accelerators

You Say Speed, I Say Energy

Matter can't travel faster than the speed of light. The closer a particle is pushed to that barrier, the more energy it takes to add even the most minute speed boost.

So, once a particle reaches 99.99 percent the speed of light, as routinely happens in accelerators, any speed boost derived from pushing it harder becomes meaningless when measured in meters-per-second. Instead, physicists think in terms of a particle's momentum or energy, measured in electron volts (eV). As a result, physicists talk about boosting particles to higher energies, not higher speeds (although it's essentially the same thing).

Traditional radio frequency accelerators coax particles to higher energies through long particle racetracks, or wave paths. The Stanford Linear Accelerator, for example, can boost particles to energies of up to 50 billion electron volts, 5 GeV, along its 3.2 km length. Laser wakefield experiments, meanwhile, have achieved 1 GeV in about 1/100,000th that stretch, 3.3 cm.

Not Just Atom Smashers

Thousands of electron accelerators are in routine use everyday. These do everything from providing radiation treatments for cancer patients to sterilizing food and treating industrial materials and nuclear waste. Accelerators also help to provide the x-rays that scientists use to probe nano materials, proteins, and even archaeological artifacts. In the near term, laser wakefield technology holds out the promise of smaller, more powerful and more affordable electron accelerators for the generation of x-rays. It will probably take more time for laser wakefield acceleration to make its way into large-scale particle physics experiments akin to the LHC, the ultimate aim of much laser wakefield acceleration research.