Cutting-edge research being conducted by scientists at the U.S. Department of Energy's (DOE) SLAC National Accelerator Laboratory and Stanford University could dramatically shrink particle accelerators for science and medicine. They used a laser to accelerate electrons at a rate 10 times higher than conventional technology in a nanostructured glass chip smaller than a grain of rice.

The nanoscale patterns of SLAC and Stanford’s accelerator on a chip gleam in rainbow colors prior to being assembled and cut into their final forms. (Credit: Matt Beardsley/SLAC)

The researchers say that this technology could help enable compact accelerators and X-ray devices for medical therapy and imaging, and research in biology and materials science. Because it employs commercial lasers and low-cost, mass-production techniques, they believe it will set the stage for new generations of “tabletop” accelerators.

Their initial demonstration achieved an acceleration gradient, or amount of energy gained per length, of 300 million electronvolts per meter, roughly 10 times the acceleration provided by the current SLAC linear accelerator.

Today’s accelerators use microwaves to boost the energy of electrons, but the new technique uses ultrafast lasers to drive the accelerator. Particles are generally accelerated in two stages. First they are boosted to nearly the speed of light. Then any additional acceleration increases their energy, but not their speed.

In the accelerator-on-a-chip experiments, electrons are first accelerated to near light-speed in a conventional accelerator. Then they are focused into a tiny, half-micron-high channel within a fused silica glass chip just half a millimeter long. The channel had been patterned with precisely spaced nanoscale ridges. Infrared laser light shining on the pattern generates electrical fields that interact with the electrons in the channel to boost their energy.

Turning the accelerator on a chip into a full-fledged tabletop accelerator will require a more compact way to get the electrons up to speed before they enter the device.

One possible application is small, portable X-ray sources to improve medical care for people injured in combat, as well as provide more affordable medical imaging for hospitals and laboratories.