By Andrew Tan
Just over two miles away from the Stanford Linear Accelerator Center (SLAC), Stanford scientists have developed a prototype for a nanoscale particle accelerator — a gadget small enough to fit on a chip, and whose miniature size could offer a new approach to cancer therapy while simultaneously increasing scientific access to a highly coveted instrument.
Inspired by traditional particle accelerators, such as the two-mile-long device at SLAC National Accelerator Laboratory, the team of Stanford researchers led by Robert Byer, a photon science professor, sought to demonstrate that the technology implemented in larger accelerators could be scaled down for at-the-ready, in-lab usage.
To tackle this challenge, Byer started the Accelerator on a Chip International Program (ACHIP), collaborating with other physicists at Stanford, at SLAC and across the world. With the support of ACHIP, the Stanford scientists published an article in the Jan. 3 issue of “Science” that showcased the result of their work: a prototype silicon chip capable of accelerating electrons with an infrared laser.
Though a single chip’s particle-accelerating power pales in comparison to that of much larger machines, the chips can still, in theory, accelerate electrons up to 94% of the speed of light when strung together in the thousands. At this velocity, the high-energy particles generated by this design could have numerous applications, all while requiring only inches of space to reach maximum speed.
“The range of energies with which we’re working is the range of energies which are very useful for medical treatments, and would also be very useful for imaging materials,” said Jelena Vuckovic, an electrical engineer and one of the principal investigators for the project.
Still, potential uses of the miniature accelerator, such as minimally invasive tumor irradiation or higher-resolution microscopy, are years away, as the development of the accelerator-on-a-chip is not quite as simple as scaling down the design of larger accelerators.
“The rules of electromagnetics actually say you could just scale down the same accelerator,” said graduate student Neil Sapra, the first author of the Science paper. “The issue becomes the material and you need to reinvent all of the components of the accelerator.”
Because infrared cannot travel through copper –– the material used in most larger microwave accelerators –– the Stanford team had to recreate an accelerator with silicon, using reverse design algorithms that suggested the optimal pattern for each chip based on the amount of light energy desired. The end result was a design that, according to Vuckovic, “looks like an abstract painting.”
But with evidence that this convoluted design does in fact work, the next step for the ACHIP team is to scale the prototype up to reach energy levels that are clinically and experimentally useful, and eventually to produce a replicable design that would enable widespread access to the nanoscale particle accelerator.
“I’ve heard stories where professors at Stanford can’t get access to our own free electron laser because it’s that booked by international scientists,” Sapra said. “So it would be super cool if you could buy a free electron laser to have in your lab and every lab could have one.”
In the meantime, ACHIP, recently funded by the Moore Foundation for an additional two years of research, will continue to investigate potential applications of its technology, such as X-ray scanning, precise manipulation of chemical reactions and material analysis.
“We’ve met our milestones,” Byer said. “Now we’ve got two more years to do application, so we can use the accelerator to drive physics, drive science.”
Contact Andrew Tan at tandrew ‘at’ stanford.edu.