Lawrence Berkeley National Laboratory researchers have accelerated electrons to high energies in less than a foot using a supersonic sheet of gas and two lasers. The breakthrough represents a significant advancement in laser-plasma acceleration, a promising technique for creating small, high-energy particle accelerators with potential uses in materials science, particle physics, and medicine. The study will be published in the journal Physical Review Letters.
Researchers used a gas injector system and dual lasers to create a high-quality 10-GeV electron beam. Image Credit: Marilyn Sargent/Berkeley Lab
Scientists have successfully accelerated high-quality electron beams to over 10 billion electronvolts (10 GeV) in 30 cm. The Lawrence Berkeley National Laboratory (Berkeley Lab) of the Department of Energy spearheaded the project, with assistance from the University of Maryland.
The Berkeley Lab Laser Accelerator Center (BELLA), where the study was conducted, set a world record in 2019 for 8-GeV electrons in 20 cm. The new experiment, which also increases the beam energy, opens the door for future high-efficiency machines by producing high-quality beams at this energy level for the first time.
We have jumped from 8 GeV to 10 GeV, but we have also significantly improved the quality and energy efficiency by changing the technology we use. This is a milestone step on the path to a future plasma-based collider.
Alex Picksley, Study Lead Author and Research Scientist, Accelerator Technology & Applied Physics Division, Lawrence Berkeley National Laboratory
Plasma, a gaseous soup of charged particles that includes electrons, is used in laser-plasma accelerators (LPAs). Researchers can produce a powerful wave by delivering a powerful energy shock to the plasma over a few quadrillionths of a second. Like a surfer on an ocean wave, electrons collect energy as they travel along the crest of this plasma wave.
Completing a second beamline at BELLA in 2022 allowed the use of a dual-laser system for the new result. The first laser in this system functions as a drill, heating the plasma and creating a channel that directs the subsequent “drive” laser pulse, which speeds up the electrons. The plasma channel keeps the laser pulse focused over longer distances, which channels the laser energy similarly to how a fiber-optic cable guides light.
Researchers previously used “capillaries,” fixed-length glass or sapphire tubes, to shape the plasma. However, to achieve the new outcome, the team resorted to a system that employs several gas jets arranged in rows, much like the jets in a gas fireplace.
The lasers pass through the supersonic-moving gas sheet created by the jets to create a plasma channel. With this setup, researchers can adjust the length of their plasma and fine-tune it, enabling them to study the process at various stages with unparalleled precision.
Before, the plasma was essentially a black box. You knew what you put in and what came out at the end. This is the first time we can capture what is happening inside the accelerator at each point, showing how the laser and plasma wave evolve, at high power, frame by frame.
Carlo Benedetti, Staff Scientist, Accelerator Technology & Applied Physics Division, Lawrence Berkeley National Laboratory
Benedetti works on the theory and modeling of laser-plasma accelerators.
By comparing their models and experiments, researchers can gain tools to fine-tune the accelerator and gain confidence that they understand the physics at play. Experts utilize a code called INF&RNO, created at BELLA, to model the laser-plasma interaction.
The intricate calculations are carried out at the National Energy Research Scientific Computing Center (NERSC) at Berkeley Lab. The new results, which validate the code used in these simulations, further strengthen the models.
Another advantage of the gas jet system is its resilience. This technology can scale to very high repetition rates, which the lab aims for future particle colliders and applications because the sheet of gas has no parts to break.
Researchers demonstrated how their method created a beam that was “dark current free,” which prevented background electrons in the plasma from inadvertently accelerating.
If you have dark currents, they are sucking up the laser energy instead of accelerating your electron beam. We have gotten to a point where we can control our accelerator and suppress unwanted effects, so we are making a high-quality beam without wasting energy. That is essential as we think about the ideal laser accelerator of the future.
Jeroen van Tilborg, Staff Scientist and Deputy Director, Accelerator Technology & Applied Physics Division, Lawrence Berkeley National Laboratory
Tilborg is in charge of BELLA’s experimental program.
There are many possible uses for the technology. It might be utilized, for instance, to create particle beams for cancer therapy. Alternatively, it might power atomic-microscope-like free-electron lasers, which would aid in developing new materials and understanding biological and chemical processes.
Anthony Gonsalves, an ATAP Staff Scientist who leads accelerator work at BELLA said, “We have taken a big step towards enabling applications of these compact accelerators. For me, the beauty of this result is we have taken away restrictions on the plasma shape that limited efficiency and beam quality. We have built a platform from which we can make big improvements, and are poised to realize the amazing potential of laser-plasma accelerators.”
When scaled up to higher energies, laser-plasma accelerators may be used in basic physics and other fields. Shortly, LPAs may be used to create muon beams that aid in imaging hard-to-reach places, such as the interior of nuclear reactors, geologic features like volcanoes or mineral deposits, or architectural structures like ancient pyramids.
In the longer term, the technology might power higher-energy particle colliders, which smash charged particles together to find new particles and learn more about the forces that underlie the cosmos. BELLA researchers are currently working on creating these extremely high-energy machines by joining the components in a staged accelerator system.
“Coupling stages together gives us a realistic path to generate electrons between 10 and 100 GeV, and to build toward future particle colliders that can reach 10 TeV [teraelectronvolts]. Once the laser energy from one stage is depleted, we send in a new laser pulse, boosting the electron energy from stage to stage in series,” said Eric Esarey, Director of the BELLA Center.
Researchers need to have strong diagnostics to develop staged systems. This gives them precise control over the timing and synchronization of steps occurring in the smallest fraction of a second. It enables them to comprehend the behavior of the plasma, laser, and electron beam.
Cameron Geddes, director of Berkeley Lab’s ATAP Division said, “With this study, we have advanced the particle energy of high-quality beams in very short distances, and the efficiency with which we can make them, by using precision diagnostics that give us great laser-plasma control. Advancing laser-plasma accelerator technology has been identified as an important goal by both the U.S. Particle Physics Project Prioritization Panel (P5) and the Department of Energy’s Advanced Accelerator Development Strategy. This result is a milestone on our way to staged accelerators that are going to change the way we do our science.”
The study was funded by the Department of Energy’s Office of Science, Office of High Energy Physics, and the Defense Advanced Research Projects Agency. It used the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science user facility.
Simulation of a 10-GeV-class, channel-guided laser-plasma accelerator #physics #laser #plasma
In this simulation of the laser-plasma acceleration process generated with the INF&RNO code, a laser driver (orange) propagates to the right through a plasma (blue), generating a plasma wave. The simulation window moves at the speed of light following the laser and the plasma wave, making them appear stationary. Laser-ionized electrons (yellow) are trapped and accelerated (yellow bunch) to energies of up to 10 GeV by the strong electromagnetic fields in the plasma, after a propagation distance of 30 cm. Video Credit: Carlo Benedetti/Berkeley Lab