Electrons riding a double wave

Since they are far more compact than today’s accelerators, which can be kilometers long, plasma accelerators are considered as a promising technology for the future. An international research group has now made significant progress in the further development of this approach: With two complementary experiments at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and at the Ludwig-Maximilians-Universität Munich (LMU), the team was able to combine two different plasma technologies for the first time and build a novel hybrid accelerator. The concept could advance accelerator development and, in the long term, become the basis of highly brilliant X-ray sources for research and medicine, as the experts describe in the journal Nature Communications (DOI: 10.1038/s41467-021-23000-7).

In conventional particle accelerators, strong radio waves are guided into specially shaped metal tubes called resonators. The particles to be accelerated – which are often electrons – can ride these radio waves like surfers ride an ocean wave. But the potential of the technology is limited: Feeding too much radio wave power into the resonators creates a risk of electrical charges that can damage the component. This means that in order to bring particles to high energy levels, many resonators have to be connected in series, which makes today’s accelerators in many cases kilometers long.

That is why experts are eagerly working on an alternative: plasma acceleration. In principle, short and extremely powerful laser flashes fire into a plasma – an ionized state of matter consisting of negatively charged electrons and positively charged atomic cores. In this plasma, the laser pulse generates a strong alternating electric field, similar to the wake of a ship, which can accelerate electrons enormously over a very short distance. In theory, this means facilities can be built far more compact, shrinking an accelerator that is a hundred meters long today down to just a few meters. “This miniaturization is what makes the concept so attractive,” explains Arie Irman, a researcher at the HZDR Institute of Radiation Physics. “And we hope it will allow even small university laboratories to afford a powerful accelerator in the future.”

Read more on the HZDR website

Image: Numerical rendering of the laser-driven acceleration (left side) and a subsequent electron-driven acceleration (right side), forming together the hybrid plasma accelerator.

Credit: Alberto Martinez de la Ossa, Thomas Heinemann

Particle accelerators drive decades of discoveries at Berkeley Lab and beyond

Berkeley Lab’s expertise in accelerator technologies has spiraled out from Ernest Lawrence’s earliest cyclotron to advanced compact accelerators.

Accelerators have been at the heart of the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) since its inception in 1931, and are still a driving force in the Laboratory’s mission and its R&D program. Ernest O. Lawrence’s invention of the cyclotron, the first circular particle accelerator – and the development of progressively larger versions – led him to build on the hillside overlooking the UC Berkeley campus that is now Berkeley Lab’s home. A variety of large cyclotrons are in use today around the world, and new accelerator technologies continue to drive progress.
“Our work in accelerators and related technologies has shaped the growth and diversification of Berkeley Lab over its long history, and remains a vital core competency today,” said James Symons, associate laboratory director for Berkeley Lab’s Physical Sciences Area.

>Read more on the ALS at Berkeley Lab website

Enjoy this video:

The power of radio!

A century after the invention of radio, the oscillating electric fields initially generated for communication now perform a fundamental function in all accelerators.

Instead of being broadcast to the world, radiofrequency (RF) energy at Diamond is trapped in resonating metal cavities to generate the electric fields that bring Diamond’s electrons up to speed.

The journey of an electron from source to storage ring is a tale of high power, split-second timing and frankly terrifying voltages. It begins in the linac gun where energetic, hot electrons are sucked away from a metal cathode by 90,000 volts and directed into the linear accelerator, or linac. The electrons travel down the linac together with precisely timed 16 megawatt blasts of microwaves generated by klystron amplifiers that themselves operate at pulsed voltages in excess of 200,000 volts. Electrons are accelerated towards the speed of light in the linac and then injected into the booster synchrotron where they complete many orbits over a tenth of a second.

>Read more on the Diamond Light Source website

Image: The linac, with the gun at the far end and the accelerating structures coming towards us.