Laser-powered Technology Boosts Electron Speed in Miniature Accelerators

Someday, potent particle accelerators could be small enough to fit in your pocket.

Two groups of physicists have achieved a milestone by creating diminutive structures that can accelerate electrons and maintain them in a controllable beam, avoiding the random dispersion. This represents an unprecedented feat for such micro accelerators and it is an essential stride towards rendering these devices more practical and common.

“One of the key issues with particle accelerators … is their gargantuan size and hefty price tags,” says physicist Jared Maxson of Cornell University, who wasn’t part of the recent research. The process of shrinking these machines could enable the creation of high-energy electrons on a tabletop, suggests Maxson. This has the potential to revolutionize medicine and scientific research.

The accelerators are built on silicon chips and comprise two rows of towers, each around 2 micrometers tall. Reminiscent of rows of tiny skyscrapers, these pillars, when struck with laser light, generate electromagnetic fields. These electromagnetic fields propel the subatomic particles at increased speed along an exceedingly narrow path in-between the pillars, which is less than a micrometer wide.

In one device, electrons gained 12.3 kiloelectron volts of energy over a distance of half a millimeter, a notable 43 percent increase that propelled the particles to 40.7 kiloelectron volts, informs physicist Peter Hommelhoff and his colleagues in their October 18 report in Nature.

Furthermore, the cautious placement of gaps in-between the pillars aid in keeping the electron beam under control, effectively emulating the capacities of their larger counterparts. “This is genuinely the first accelerator based on nanophotonics encapsulating all the features that a modern accelerator should have,“ claims Hommelhoff, associated with the University of Erlangen-Nuremberg in Germany.

A similar accomplishment was announced on October 3 by physicist Robert Byer of Stanford University and his team, reporting energy gains of up to 23.7 kiloelectron volts. Both teams are part of a broader consortium titled the Accelerator on a Chip International Program, or ACHIP, consolidating endeavors to construct these micro accelerators.

The title of the most potent particle accelerator in the world goes to the Large Hadron Collider, or LHC, near Geneva, with a massive 27-kilometer ring. The new miniature accelerators, with mere thousands of electron volts, won’t be responsible for the discovery of Higgs bosons any time soon, a particle discovered at the LHC in 2012.

However, these devices could have their unique applications. High-energy electrons used for skin cancer treatment by causing damage to the DNA of cancer cells and killing them could become much more widely available with an accelerator built on a chip, as the current process requires a room full of heavy machinery.

Moreover, similar treatments could be applicable beyond skin depth. “The aspiration is to have a fiber that can enter a human body for a localized radiation treatment because the entire accelerator can be accommodated within you,” suggests Pietro Musumeci of UCLA, a member of ACHIP who wasn't part of these new findings.

The miniature accelerators might be used to create particular light states potentially useful for quantum computing. Alternatively, they could be useful for research on materials, possibly creating images of thin materials with an extraordinarily high temporal resolution.

Despite the promise, these accelerators have a long journey ahead. The electron emission rate from these machines is significantly lower compared to conventional accelerators. And while they can focus the beam in two dimensions, more work is needed to attain vertical focus.

The energy gains of these devices need further enhancement too. While the energy accumulated by the electrons over a given acceleration distance is relatively the same as conventional accelerators, scientists aim to far surpass the conventional with billions of electron volts per meter.

Nonetheless, this work exemplifies techniques that once seemed ridiculous to even attempt. Initially, when Byer shared the idea with his colleagues, “they’d just burst out laughing,” he recalls. “No one’s laughing now; instead, they’re appreciative.”

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