Strong open field quantum electrodynamics cracking

A recently published theoretical and computer modeling study suggests that the world’s most powerful lasers may finally decipher the elusive physics behind some of the universe’s most extreme phenomena – gamma-ray bursts, pulsar magnetospheres, and more.

The international research team behind the study includes researchers from the Lawrence Berkeley National Laboratory (Berkeley Lab) and the Commission for Atomic Energy and Alternative Energies (CEA-LIDYL). They report their findings in the prestigious journal Physical examination letters.

The research team was led by Henri Vincenti from CEA, who proposed the main physical concept. Jean-Luc Vay and Andrew Myers, of the Accelerator Technology and Applied Physics (ATAP) and Computational Research Division of Berkeley Lab, respectively, led the development of the simulation code used for the research. (Vincenti previously worked at the Berkeley Lab as a Marie Curie researcher and remains an ATAP affiliate and frequent collaborator.) Theoretical and numerical work was led by Luca Fedeli of the Vincenti team at CEA.

The team’s modeling study shows that petawatt-class (PW) lasers – reduced to even higher intensities via light-matter interactions – could provide a key to unraveling the mysteries of the strong-field regime (SF ) of quantum electrodynamics (QED). A petawatt is 1 times ten at the fifteenth power (i.e., followed by 15 zeros), or a quadrillion watts. The output of today’s most powerful lasers is measured in petawatts.

“This is a powerful demonstration of how advanced simulation of complex systems can open new avenues for discovery science by integrating multiple physical processes – in this case, the laser interaction with a target and the subsequent production of particles in a second target, “said the ATAP division. Director Cameron Geddes.

Lasers probe some of nature’s most closely guarded secrets

While QED is a cornerstone of modern physics that has withstood the rigors of experiment for many decades, probing SF-QED requires electromagnetic fields with an intensity of several orders of magnitude beyond those normally available on Earth.

Researchers have tried secondary pathways to SF-QED, such as using powerful particle beams from accelerators to observe the interactions of particles with the strong fields that are naturally present in certain aligned crystals.

For a more direct approach, the highest electromagnetic fields available in a laboratory are delivered by class PW lasers. A 10-PW laser (the most powerful in the world today), focused down to a few microns, can reach intensities close to 10²³ watts per square centimeter. The associated electric field values ​​can reach 10¹⁴ volts per meter. Yet studying SF-QED requires even higher field amplitudes than that, orders of magnitude beyond what can be achieved with these lasers.

To break this barrier, the researchers planned to use powerful electron beams, accessible in large accelerators or laser installations. When a high power laser pulse collides with a relativistic electron beam, the amplitude of the laser field seen by the electrons in their resting frame can be increased by several orders of magnitude, giving access to new SF regimes. -QED.

Although such methods are experimentally difficult, as they require the synchronization in space and time of a high power laser pulse and a relativistic electron beam at the femtosecond scale and micron, a few experiments of this type have been carried out successfully, and several more are planned around the world in PW-class laser installations.

Using a movable curved plasma mirror for a direct gaze

The research team proposed a complementary method: a compact scheme that can directly increase the intensity of existing high power laser beams. It is based on a well-known concept of light intensification and their theoretical studies and computer modeling.

The scheme consists in increasing the intensity of a PW laser pulse with a relativistic plasma mirror. Such a mirror can be formed when an ultra high intensity laser beam strikes an optically polished solid target. Due to the high amplitude of the laser, the solid target is fully ionized, forming a dense plasma which reflects incident light. At the same time, the reflecting surface is actually moved by the intense laser field. As a result of this movement, part of the reflected laser pulse is temporally compressed and converted to a shorter wavelength by Doppler effect.

The laser radiation pressure gives this plasma mirror a natural curvature. This focuses the Doppler-enhanced beam to much smaller points, which can result in extreme intensity gains (over three orders of magnitude) where the Doppler-enhanced laser beam is focused. The simulations indicate that a secondary target at this focus would give clear SF-QED signatures in real experiments.

Berkeley Lab is an integral part of the international team research effort

The study drew on the various scientific resources of Berkeley Lab, including its simulation code WarpX, which was developed to model advanced particle accelerators under the auspices of the US Department of the United States Department’s Exascale Computing Project. Energy. The new capabilities of WarpX made it possible to model the increase in intensity and the interaction of the amplified pulse with the target. All previous simulation studies have only been able to explore proof-of-principle configurations.

Experimental verification of the research team’s methodology for probing SF-QED could come from the Berkeley Lab Laser Accelerator (BELLA), a petawatt-class laser with an unprecedented repetition rate at this power of one pulse per second. A second beamline is currently under construction that could also contribute to experimental studies of SF-QED by researchers at the Berkeley Lab. A proposed new laser, kBELLA, could enable future high throughput studies by bringing high intensity at a kilohertz repetition rate to the facility.

The discovery via WarpX of new high intensity laser-plasma interaction regimes could have benefits far beyond ideas for exploring SF-QED. This involves better understanding and designing plasma accelerators such as those under development at BELLA. More compact and less expensive than conventional accelerators of similar energy, they could ultimately be a game-changer in applications ranging from extending the reach of high-energy physics and penetrating photon sources to precision imaging. to ion implantation in semiconductors, to cancer treatment, to develop new pharmaceuticals, and more.

“It’s gratifying to be able to help validate potentially powerful new ideas through the use of our new algorithms and codes,” Vay said of the Berkeley Lab team’s contributions to the study. “This is part of the beauty of collaborative science as a team. ”