Compact Accelerator Achieves a Major Energy Milestone

A compact particle accelerator developed by the University of Texas at Austin, several national laboratories, and the Texas-based company TAU Systems has produced an electron beam with an energy of 10 billion electron volts (10 GeV). The accelerator, less than 20 m long, is among three in the United States capable of producing an energy level that high, though the other two are both approximately 3 km long.

“We can now reach those energies in 10 cm,” 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.

This gas cell is a key component of a compact wakefield laser accelerator developed at the University of Texas at Austin. Inside, an extremely powerful laser strikes helium gas, heats it into a plasma, and creates waves that kick out electrons from the gas in a high-energy electron beam. Courtesy of Bjorn Manuel Hegelich/UT Austin.

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.

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 advancement 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.

“It’s hard to get into a big wave without getting overpowered, so wake surfers get dragged in by Jet Skis,” Hegelich said. “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, and that’s our secret sauce.”

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 1000 times the installed electrical power in the U.S. but lasts only 150 fs, less than a billionth as long as a lightning discharge. The researchers’ long-term goal is to drive their system with a laser they’re 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.

A gas cell drawing. Inside, an extremely powerful laser strikes helium gas, heats it into a plasma, and creates waves that kick out electrons from the gas in a high-energy electron beam. Nanoparticles, generated by a secondary laser shining through the top window and striking a metal plate, boost the energy transferred to the electrons. Courtesy of UT Austin.

Hegelich and Constantin Aniculaesei, corresponding author now at Heinrich Heine University Düsseldorf, Germany, 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. As part of the agreement, UT has been issued shares in TAU Systems.

Support for this research was provided by the U.S. Air Force Office of Scientific Research, the U.S. Department of Energy, the U.K. Engineering and Physical Sciences Research Council, and the European Union’s Horizon 2020 research and innovation program.

TAU Systems recently signed a lease for a 22,300-sq-ft building located at the Carlsbad Research Center in California. There, it will establish TAU Labs, the first of its light-source applications and R&D centers. The facility will feature several laser-driven particle and light sources, and will provide industrial users with access to EUV and x-ray light sources, as well as MeV electrons and other particle beams.

The application center will begin accepting particle and light-source customers upon completion of the first phase of construction in 2024. According to the company, TAU Labs will offer radiation testing for space-bound electronics, in addition to its R&D activities.

The research was published in Matter and Radiation at Extremes (www.doi.org/10.1063/5.0161687).