Compact electron accelerator reaches new speeds with nothing but light
An image from a simulation in which a laser pulse (red) drives a plasma wave, accelerating electrons in its wake. The bright yellow spot is the area with the highest concentration of electrons. In an experiment, scientists used this technique to accelerate electrons to nearly the speed of light over a span of just 20 centimeters. Credit: Bo Miao/IREAP

The scientists harnessed precise control of ultrafast lasers accelerated electrons over a 20-centimeter stretch to speeds usually reserved for particle accelerators.

The team headed by Professor of Physics and Electrical and Computer Engineering at the University of Maryland, in collaboration with the team at Colorado State University, achieved this feat using two laser pulse sent through a jet of hydrogen gas The hydrogen was torn apart by the first pulse and a hole was created by the second pulse. The channel guided a second, higher power pulse that picked up electrons out of the Plasma and dragged them along in its wake, speeding them up to nearly the speed of light.

The team was able to accelerate electrons to 40% of the energy achieved at the Linac Coherent Light Source. The paper was accepted for publication in the journal.

The Institute of Research Electronics and Applied Physics at the University of Maryland has a multi-GeV electron accelerator that is powered by lasers. With lasers becoming cheaper and more efficient, we believe that our technique will become the way to go for researchers in this field.

The energy of an electron that's moving at 99.99999983% the speed of light is accelerated by the LCLS, a kilometer-long runway. Three discoveries about fundamental particles were made by L CLS's predecessor. The LCLS uses super-fast electrons to generate the most powerful X-ray laser beams. Scientists use X-rays to peer inside atoms and create videos of chemical reactions Drug discovery, energy storage, and innovation are some of the things that these videos can help with.

It is difficult to accelerate electrons to GeV energies. The electrons are pushed by the electric fields in the metal tubes. The tubes would be damaged if the electric fields were any more powerful. Being unable to push electrons harder, researchers have decided to just push them for longer. The kilometer long slice is across northern California. The teams worked to boost electrons to nearly the speed of light using light itself to bring this technology to a more manageable scale.

The goal is to shrink GeV-scale electron accelerators to a modest size room, according to Jaron Shrock, a graduate student in physics. You have a factor of 1000 stronger field when you take kilometer-scale devices. The goal is to take kilometer-scale to meter-scale.

A process called laser wakefield acceleration can be used to create stronger fields in a lab, in which a pulse of tightly focused and intense laser light is sent through a Plasma.

Bo Miao is a physicist at the University of Maryland and co-first author on the work. The electrons are pushed out of the path of the laser pulse because it is so strong. The electrons travel in the pulse's wake by looping around the boat.

The first demonstration of laser wakefield acceleration took place in 1995. It was only a couple of centimeters away from being able to accelerate electrons. The UMD team pioneered a technique to tame the high-energy beam and keep it from spreading its energy too thin, which allowed the team to leverage wakefield acceleration more effectively than ever before. The technique they use punches a hole through the plasma and creates a waveguide to keep the beam's energy focused.

Shrock explains that a pulse can be propagation over a long distance. The high energy of the pulse would destroy a traditional cable. It's not possible to destroy Plasma because it already is.

The things that carry internet service and other communications signals out of thin air are created by their technique. Out of the jets of hydrogen gas.

There is a central "core" guiding the light and a surrounding "cladding" to prevent the light from leaking out. The team used a jet of hydrogen gas and a laser beam. As this additional "guiding" laser travels through the jet, it takes the electrons off the hydrogen atoms. A lower density "core" and a higher density gas on its fringe are created by the rapid expansion of the Plasma. This channel is used to send the main laser beam. The front edge of this pulse creates the "cladding" by turning the higher density shell to the lower density one.

"It's like the very first pulse clears an area, and then the high-intensity pulse comes down like a train with someone standing at the front throwing down the tracks," says Shrock.

The researchers were able to accelerate some of their electrons to 5 GeV with the help of the CSU team. That honor belongs to a team at Lawrence Berkeley National Labs who achieved the maximum with laser wakefield acceleration. The team says their technique is more versatile and can potentially produce electron bursts thousands of times per second, making it a promising technique for many applications. The success of the method will allow the team to improve the setup and increase the speed.

The energy distribution is less than ideal because the electrons are generated along the full length. "We can improve the design so that we can control where they are precisely injected, and then we can better control the quality of the beam."

The authors say that this work shows a path forward, even though the dream of LCLS on a table is not a reality yet. Between now and then a lot of engineering and science needs to be done. The electrons have the same energy and travel in the same direction. There are ways to improve the beam attributes in wakefield lasers. If we want to achieve energies on the scale of tens of GeV, we'll need to stage multiple wakefield accelerators, passing the accelerated electrons from one stage to the next while preserving the beam quality. There is a long way to go between now and having an LCLS facility.

More information: B. Miao et al, Multi-GeV Electron Bunches from an All-Optical Laser Wakefield Accelerator, Physical Review X (2022). DOI: 10.1103/PhysRevX.12.031038 Journal information: Physical Review X