Berkeley Lab

A Novel Technique for Producing Positron Beams Using Laser-Plasma Accelerators

Schematic showing an electron beam (coming from the left, in blue) hits a thick tungsten target, and e+e- pairs are generated via bremsstrahlung. A laser pulse (coming from the top) impinges on the back surface of the target and is reflected by a plasma mirror to the right, where it excites a plasma wave. Positrons exiting the target (in green) are trapped and accelerated in the wake. (Credit: Davide Terzani/Berkeley Lab)

By Davide Terzani, February 22, 2024


Researchers from the BELLA Center in the Accelerator Technology & Applied Physics Division at Berkeley Lab have used computer simulations to design a compact, all-optical device to produce and accelerate positron beams. The work shows that reducing the transport distance between the production and accelerating stages enables the injection of these beams into a plasma-based accelerator.


The work provides a technique for generating compact positron beams for injection into a laser-driven plasma accelerator, allowing future experiments at BELLA on positron acceleration in laser-driven plasma-based accelerators that do not require building a large conventional positron beamline.

Particle colliders for the next generation of physicists

Particle colliders are complex scientific instruments designed to accelerate charged particles to extremely high energies and collide them. Since their development in the second half of the 20th century, colliders have enabled numerous groundbreaking discoveries and played a pivotal role in advancing our understanding of fundamental particles and the laws of physics. However, conventional accelerator technologies such as radiofrequency cavities—the backbone of particle colliders for decades—now face challenges in accelerating particles to higher energies.

Plasma-based acceleration is attracting considerable attention because it can achieve higher accelerating gradients than traditional methods, promising compact colliders with significantly reduced footprints compared to today’s machines. Indeed, the recently released Particle Physics Project Prioritization Panel (P5) Report, which outlines a pathway for particle physics over the next decade, has identified laser-plasma accelerators as a path to next-generation particle colliders to uncover new physics at the 10 TeV per parton scale.

Producing and trapping positron beams

Realizing a plasma-based electron-positron collider presents its own set of challenges. One major obstacle is producing and injecting a positron beam—the antimatter counterpart of electrons—into the plasma. Overcoming this technological hurdle is important for realizing the next generation of plasma-based particle colliders.

Davide Terzani (right), a project scientist in the BELLA Center, and Carl Schroeder (left), senior scientist and deputy director of BELLA, describe to Gianmarco Parise (middle), a visiting student, the concept of a positron injector that they have developed. (Credit: Asmita Patel/Berkeley Lab)

While positron beams can be produced in heavy materials using processes like electron-positron pair production, existing positron production and trapping techniques face obstacles when applied to plasma acceleration. For instance, a plasma-based accelerating stage is characterized by a small transverse and longitudinal acceptance of about 100 μm. Current techniques, however, can typically only produce beams with a much larger transverse size.

This work achieves positron trapping by reducing the coupling distance between the positron production and accelerating stages before the beam expands and elongates significantly. The production target acts as a plasma mirror that couples the laser pulse to the subsequent plasma stage to drive the accelerating and trapping wake, reducing the inter-stage distance to only a few centimeters.

With an appropriate delay, the positron beam is injected directly into the accelerating and focusing phase of the plasma wave generated by the in-coupled laser. By correctly tuning the laser and plasma parameters, it is possible to accelerate positron beams of substantial charge (up to tens of picocoulombs) to an energy of 1 GeV and beyond. The work will enable a compact platform to experimentally explore and optimize staged laser-plasma acceleration of positron beams for a future electron-positron collider based on laser-plasma accelerators.

Contact: Davide Terzani

Researchers: Davide Terzani, Carlo Benedetti, Stepan Bulanov, Carl Schroeder, Eric Esarey

Funding: This research was supported by the U.S. Department of Energy Office of High Energy Physics. The work was conducted at the National Energy Research Scientific Computing Center at Berkeley Lab.

Publication: D. Terzani, C. Benedetti, S. S. Bulanov, C. B. Schroeder, and E. Esarey. “Compact, all-optical positron production and collection scheme,” Phys. Rev. Accel. Beams, vol. 26, no. 11, p. 113401, November 2023,


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