The Pocket-Sized Particle Accelerator

Researchers have built a particle accelerator that fits on a silicon-chip with a wealth of possible applications, including in the battle against cancer.

This image, magnified 25,000 times, shows a section of a prototype accelerator-on-a-chip. The segment shown here is one-tenth the width of a human. The oddly-shaped grey structures are nanometer-sized features carved into silicon that focus bursts of infrared laser light, shown in yellow and purple, on a flow of electrons through the centre channel. As the electrons travel from left to right, the light focused in the channel is carefully synchronized with passing particles to move them forward at greater and greater velocities. By packing 1,000 of these acceleration channels onto an inch-sized chip, Stanford researchers hope to create an electron beam that moves at 94 per cent of the speed of light and to use this energized particle flow for research and medical applications. (Neil Sapra)

At Stanford University there exists a powerful juxtaposition in the field of particle acceleration. On the hillside overlooking the University sits the SLAC National Accelerator Laboratory, which houses a 2-mile long, linear particle accelerator. Meanwhile, in its shadow, scientists at SLAC and Stanford have developed a particle accelerator that does the same job but can also fit on a silicon chip.

Of course, such a disparity in size does create other major differences. Whilst the giant accelerator fires streams of electrons through a vacuum pipe with bursts of microwave radiation pushing them to near light speed, the pocket-sized particle accelerator can accelerate electrons to only a fraction of that velocity. This is still an impressive feat, however, as the infrared laser used by the mini-accelerator can deliver enough energy in just the width of a hair to push the electron to this speed. The same boost in the larger equipment takes the microwaves many feet to impart.

The accelerator-on-a-chip is just a prototype, but its design and fabrication techniques can be scaled up…