Texas compact accelerator achieves ‘major energy milestone’

28 Nov 2023

University of Texas, Tau Systems, and partners demo compact particle accelerator yielding 10 GeV e-beam.

Particle accelerators present great potential for semiconductor applications, medical imaging and therapy, as well as research into materials, energy and medicine. But conventional accelerators require plenty of space – even up to the kilometer scale – making them expensive and usually limiting their presence to a handful of national labs and universities.

Now researchers from the University of Texas at Austin, several national laboratories, European universities and the Texas-based company Tau Systems have demonstrated a compact particle accelerator less than 20 m long that produces an electron beam with an energy of 10 GeV.

There are only two other accelerators currently operating in the U.S. that can reach such high electron energies, but both are approximately 3 km long.

“We can now reach those energies in 10 centimeters,” said Bjorn “Manuel” Hegelich, associate professor of physics at UT and CEO of Tau Systems, referring to the size of the chamber where the beam was produced. He is the senior author on a recent paper describing their achievement in Matter and Radiation at Extremes.

Hegelich and his team are currently exploring the use of their accelerator, called an Advanced Wakefield Laser Accelerator, for a variety of purposes. They hope to use it to test how well space-bound electronics can withstand radiation, to image the 3D internal structures of new semiconductor chip designs, and even to develop novel cancer therapies and advanced medical-imaging techniques.

Laser driver

This kind of accelerator could also be used to drive another device called an X-ray free electron laser, which could take slow-motion movies of processes on the atomic or molecular scale. Examples of such processes include drug interactions with cells, changes inside batteries that might cause them to catch fire, chemical reactions inside solar panels, and viral proteins changing shape when infecting cells.

The concept for Wakefield laser accelerators was first described in 1979. An extremely powerful laser strikes helium gas, heats it into a plasma and creates waves that kick electrons from the gas out in a high-energy electron beam.

During the past couple of decades, various research groups have developed more powerful versions. Hegelich and his team’s key advance relies on nanoparticles. An auxiliary laser strikes a metal plate inside the gas cell, which injects a stream of metal nanoparticles that boost the energy delivered to electrons from the waves.

The laser is likened to a boat skimming across a lake, leaving behind a wake, and electrons ride this plasma wave like surfers. “It's hard to get into a big wave without getting overpowered, so wake surfers get dragged in by jet skis,” said Hegelich.

Wave-nanoparticle model

He added, “In our accelerator, the equivalent of jet skis are nanoparticles that release electrons at just the right point and just the right time, so they are all sitting there in the wave. We get a lot more electrons into the wave when and where we want them to be, rather than statistically distributed over the whole interaction.”

For this experiment, the researchers used one of the world's most powerful pulsed lasers, the Texas Petawatt Laser, which is housed at UT and fires one ultra-intense pulse of light every hour. A single petawatt laser pulse contains about 1,000 times the installed electrical power in the U.S. but lasts only 150 femtoseconds.

The team’s long-term goal is to drive their system with a laser they are currently developing that fits on a tabletop and can fire repeatedly at thousands of times per second – making the whole accelerator far more compact and usable in much wider settings than conventional accelerators.

Hegelich and Aniculaesei have submitted a patent application describing the device and method to generate nanoparticles in a gas cell. Tau Systems, spun out of Hegelich’s lab, holds an exclusive license from the University for this foundational patent.