CERN prepares to test revolutionary mini-accelerator

On 18 September, the council that governs CERN, Europe’s premier particle-physics laboratory, near Geneva, Switzerland, approved a boost in funding for a planned experiment called the Advanced Wakefield Experiment, or AWAKE. Due to switch on next year, AWAKE will accelerate particles by ‘surfing’ them on waves of electric charge created in a plasma, or ionized gas. It is a method that could allow future accelerators to probe matter and the forces of nature at ever-higher energies, without the usual accompanying increase in the instruments’ size and therefore cost.

Although plans are afoot to build bigger machines once the LHC reaches the end of its life in the 2030s, many fear that accelerator size is nearing its limit and that such proposals may simply prove too expensive to implement.

“When you look at cost estimates for these machines and the scale of machines, you understand that maybe a new breakthrough regime is needed,” says Nick Walker, an accelerator physicist at DESY, Germany’s high-energy-physics laboratory in Hamburg.

Conventional colliders, such as the 27-kilometre-long LHC, use electric fields to move charged particles through a tunnel; the fields switch from positive to negative at a frequency that means the particles are constantly nudged forward, gaining energy with each push. But such colliders use metal-walled cavities that spark if the electric field is too strong. As a result, the only way to further increase the particles’ speed, and therefore energy, is to lengthen the tunnel.

Plasma wakefield accelerators, which were first proposed in the 1970s, are designed to break this cycle, says physicist Allen Caldwell at the Max Planck Institute for Physics in Munich, Germany, who will lead the AWAKE experiment. They send a pulse of charged particles or laser light through a plasma, which sets electrons and positively charged ions oscillating in its wake. The resulting regions of alternating negative and positive charge form waves that accelerate further charged particles. Injected at just the right time, these particles effectively surf the waves (see ‘Wakefield acceleration’). Crucially, as the electric fields are much stronger than those in a conventional collider, the acceleration can be as much as 1,000 times greater over the same distance.

Credit to Nature.com