Physicists worldwide have been looking at alternatives for large particle accelerators. Some have managed to develop small “tabletop” accelerators, but to produce the same acceleration, it would require researchers to connect many of them together.

Now, a team of researchers from the Lawrence Berkeley National Laboratory (Berkeley Lab) has been able to link two tabletop accelerators together. They boosted electrons to multi-billion electron-volt energies in just a few centimeters, a distance much shorter than what can be achieved with conventional accelerators but still significant. The results are reported in Nature.

In the last 100 years, particle physics has been unlocking the secrets of the quantum world by smashing particles together. The smaller the scale, the higher the energy we need to provide. Unfortunately, the higher the energy needed, the bigger the particle accelerator has to be, so physicists have been looking at linking smaller accelerators together to reduce costs without affecting performance.

Tabletop accelerators, also called laser-plasma accelerators (LPAs), use laser pulses to accelerate electrons. An ideal linked system will have a beam of electrons moving through a series of accelerators, where it would be accelerated by a new laser pulse.

The second laser pulse is critical and it requires the use of a special mirror. The mirror needs to allow electrons through but also pass enough energy onto the beam. Unfortunately, the laser has to be so close to the mirror that it would blow a hole through any material that doesn’t affect electrons.

^{Schematic of the first experiment to achieve staging of laser-plasma accelerators (LPAs) with independent laser pulses. Berkeley Lab}

"We decided from the beginning of the project that instead of worrying about blowing up the mirror, we'd blow it up with every shot," says Wim Leemans, co-author of the paper, in a statement. They first developed a prototype mirror of water film, he says, "but settled for much more robust VHS tape."

VHS tape is thin, stretch-resistant and can run for hours at a time. Most importantly, when hit by the laser it creates a dense flat plasma, which acts as a highly efficient mirror.

"Many groups around the world are working on different aspects of LPA development, and I am confident that we will see the first applications of LPAs in the coming decade," says James Symons, associate laboratory director for physical sciences at Berkeley Lab. "As with all new technologies, the nature of those applications may surprise us."