Demonstration of active plasma lensing

Our group has participated in an experiment at CERN which found a simple way to suppress one of the main aberrations of the so-called active plasma lens—a compact focusing device for high energy particle beams—demonstrating for the first time that such beams can be focused without degrading the beam quality. 
 
Building smaller accelerators has been a goal of the particle accelerator community for decades, resulting in the development of both new accelerating mechanisms and new ways of focusing particle beams. Active plasma lensing is one such technique, where a large electric current sets up strong magnetic fields in a plasma, that focus high-energy beams in not meters but centimeters. However, the large current also heats the plasma in a way that leads to imperfect focusing—an aberration—much like in a faulty glass lens that gives an unclear image. This leads to an undesirable degradation of the particle beam quality. 
 
Recently, an international team of scientists working at the CLEAR User Facility at CERN discovered that this aberration could be suppressed by simply changing the gas used to make the plasma—from a conventional light gas (helium) to a heavier gas (argon). Changing the gas slows down the heat transfer so that the aberration does not have time to form. The team showed that this resulted in an ideal lens, and was able to demonstrate degradation-free focusing of an electron beam for the first time in an active plasma lens. The results are a significant step towards making active plasma lenses a standard accelerator component in the future.
 
The key contribution of the Oxford group to these results was work led by Anthony Dyson on the development of compact Marx bank circuits for driving the capillary discharge, as previously published in Review of Scientific Instruments.
 
The new research on active plasma lenses has been published in Physical Review Letters.
 
Active Plasma Lense