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New particle accelerator can rest on your fingertip

Portable X-rays could result from a new particle accelerator chip that uses cheaper laser technology and less material to work. 

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Stanford scientists have developed an accelerator chip that is only about a few millimeters wide.

Brad Plummer/SLAC

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Imagine an X-ray machine small enough to fit on a table top.  

Stanford researchers have brought us one step closer to this technology by creating a particle accelerator smaller than a grain of rice. The device paves the way for cheaper and smaller accelerators that could mean big things for science and medicine.

"Our sponsor of this work is DARPA [the Defense Advanced Research Projects Agency], and DARPA wants us to develop an accelerator and an X-ray source that can be portable so that you could carry the X-ray machine into the field and use it to provide medical care for injured soldiers," said Robert Byer, principal investigator of the study.

Particle accelerators are typically clunky and costly. X-rays use accelerators to produce the images seen on film – electrons accelerated through a tube collide with atoms to create X-rays. Most accelerators use microwaves to accelerate the electrons to nearly the speed of light through a linear or circular track.

This track can be massive; the largest particle accelerator at CERN in Geneva runs about 17 miles around. But the Stanford team used an infrared laser to move their electrons through a channel finer than a human hair.

Byer compares the science of accelerators to a surfer.

"If you imagine a surfer riding a wave in the ocean, there's sort of two things a surfer has to do to ride the wave," he said. "One is be in the right place at the right time...and then you have to pre-accelerate,  you have to paddle to catch up to go about the about the same speed as the wave."

After getting electrons up to nearly the speed of light in a  conventional accelerator, researchers funneled the particles through a tiny channel less than 1/200th the width of a human hair. Instead of exposing the particles to microwaves, the team used lasers.  

The key part of their design was using nanoridges in the channel so that the particles could gain energy as they travel. The light waves from the laser have two electric forces: a positive one that accelerates an electron, and a negative one that slows it down.

The ridges allow the electron to be less affected by the negative charge that saps it of energy. Without them, Byer explained, the electrons would not gain any energy but just shimmy back and forth. 

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