Researchers capture a detailed picture of electron acceleration in a single shot

Tweaking experimental methods has produced the first “single-shot” diagnosis of electron acceleration by a laser wakefield accelerator along a curved trajectory, according to a recent study led by researchers at the University of Michigan. The findings are published in the journal Physical Review Letters.

This optical technique could help engineers develop more powerful electron accelerators for fundamental studies of quantum and particle physics – or more compact accelerators for use in medicine and industry.

Compared to traditional accelerators that can be kilometers long, wakefield laser accelerators can apply 1000 times more energy per meter, allowing for a much more compact design capable of fitting into a large room.

The device fires a laser through a vapor, creating an ionized plasma, then separates electrons from ions, which creates a “wake field,” similar to the wake a boat leaves behind as it moves through water. It then injects a beam of electrons into the accelerator which “surf” behind, rapidly gaining energy.

“The beam of particles coming out of a laser plasma accelerator is so short-lived that it would take less time for light to travel the width of a hair. The whole acceleration process is so fast, at a trillionth of a second time scale, that it is extremely difficult to measure,” said Alexander Thomas, professor of nuclear engineering and radiological sciences, electrical and computer engineering, and physics at UM and lead author of the study.

Until now, electron acceleration processes have been measured through several experimental rounds, called multi-shot mode, but those methods rely on the stability and reproducibility of the accelerator – leaving room for variation between experiments.

“It is essential to accurately diagnose the electron acceleration process in order to maximize the electron energy gain. This could be a crucial step to push forward the development of future teraelectronvolt (TeV) lepton colliders used to understand the fundamental laws of nature,” said Thomas. .

The research team made the diagnosis of single-shot electron acceleration during an experiment on a laser wakefield accelerator at the Advanced Laser Light Source of the Institut National de la Recherche Scientifique in Quebec, Canada.

The technique is based on a phenomenon that occurs during the acceleration of the laser wake field, known as “betatron X-ray radiation”, where electrons emit high-energy photons in the X-ray region of the electromagnetic spectrum as they oscillate transverse.

“In our work, we direct the intense laser light with a plasma density ramp so that the laser light follows a curved trajectory, just like the electron beam accelerated in the wake of the laser light,” said Yong Ma, assistant researcher at nuclear engineering and radiological sciences at UM and corresponding author of the study.

The photons emitted by the electron always follow the tangent direction of its instantaneous trajectory. Thus, photons emitted at different times appear at different angles and thus at different spatial locations on a screen.

The properties of the photons, namely the photon energies and angular distribution, are completely determined by the properties of the electron beam. Therefore, by measuring the spatially resolved photon properties, the researchers were able to piece together the electron acceleration process from a single experiment.

“We had this basic idea using the so-called ‘betatron streaking’ technique seven years ago and demonstrated its feasibility using numerical simulations. It was quite an interesting and fun experience to conduct an experiment based on numerical simulations and get the expected experimental results,” said Ma.

“It’s a great result that could open new avenues for a detailed understanding of laser-plasma accelerators,” said Dr. Daniel Seipt of the Helmholtz Institute Jena, lead author of the study, who provided the theoretical support.

The results could find applications in advanced control of laser beam and particle propagation, for example, the development of curved plasma channels for coupling multistage laser accelerators.

A multi-stage wakefield accelerator would overcome the energy limitations of a single-stage accelerator, achieving higher particle energies. These high energies could be used for quantum mechanics experiments similar to those done at CERN’s Large Hadron Collider, but on a smaller, less expensive scale.

Beyond quantum exploration, multistage laser accelerators could eventually be applied to practical use for targeted tumor destruction in cancer treatments or cutting materials with limited heat damage in industrial settings.