Gain greater control over plasma accelerators by combining acceleration methods

Demonstration of wake-up fields in a two-stage plasma accelerator. Credit: Moritz Förster

If one particle accelerator alone is not enough to achieve the desired result, why not combine the two accelerators? An international team led by physicists at the Center for Advanced Laser Applications (CALA) at LMU Munich brought the idea to life. He combined two plasma-based acceleration methods for electrons, namely a laser-driven wake-field accelerator (LWFA) and a particle-beam-driven wake-field accelerator (PWFA).

With this combination, physicists achieve better stability and higher particle density for electron beams than with a single plasma accelerator. The innovative concept therefore opens up new perspectives for plasma-based particle acceleration.

Plasma-based wake field acceleration is considered a hot candidate for next-generation particle accelerators. In such a machine, a dense drive moves through a mixture of particles called plasma and ions and free electrons. Either an intense laser pulse or a short, very intense pulse of high-energy particles, the drive displaces plasma electrons that get in its way.

Similar to a boat on a lake, the displaced substance returns to its original position behind the driver. On the resulting trail behind the driver, the electrons can travel in sequence and reach energies in the gigaelectronvolt range within a few millimeters. However, due to their enormously large acceleration fields, these plasma accelerators are difficult to tame.

CALA laser physicists have now experimentally demonstrated that by combining a laser-driven and an electron-beam-powered plasma accelerator, higher stability and particle density can be achieved than is possible with a single laser-driven accelerator stage. In this “hybrid” approach, high peak current electron beams are generated in the first laser-driven wake field accelerator.

Plazma hızlandırıcıları üzerinde daha fazla kontrol elde etmePhysical Examination X (2022). DOI: 10.1103/PhysRevX.12.041016″/>

Experimental setup for phased LWFA-PWFA with internal injection in the PWFA phase. (a) Schematic of the dual jet setup for the stepwise LWFA-PWFA experiments. Credit: Physical Examination X (2022). DOI: 10.1103/PhysRevX.12.041016

These electrons act as a driver for the next particle-driven wake-up field accelerator, where the electrons are accelerated again. The stability of the newly produced electron beam is much higher, as the second accelerator stage is much less sensitive to the inevitable fluctuations of the driver. Thus, the hybrid approach combines the advantages of two complementary drive types for plasma-based accelerators.

The stability of the electron beams produced and the high charge density are an essential prerequisite for the generation of bright X-rays through various mechanisms. On the one hand, narrow-band, low-aberration electron beams are ideal for generating hard X-rays with Thomson backscattering, which can be used for medical imaging.

On the other hand, high beam quality should enable challenging new applications such as plasma-based free electron lasers (FELs). This type of FEL radiation could be used in the future to study ultrafast events with atomic spatial and temporal resolution in solids.

The study was published in the journal Physical Examination X.

More information:
Stable and High Quality Electron Beams from FM Foerster et al., Stepped Laser and Plasma Wakefield Accelerators, Physical Examination X (2022). DOI: 10.1103/PhysRevX.12.041016

Provided by the Ludwig Maximilian University of Munich.

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