Awakening the potential of plasma acceleration
Civil engineering has begun for the new AWAKE experiment, which looks to push the boundaries of particle acceleration. This proof-of-principle experiment will harness the power of wakefields generated by proton beams in plasma cells, producing accelerator gradients hundreds of times higher than those used in current RF cavities.
Civil engineering works are currently ongoing at the AWAKE facility.
As one of CERN's accelerator R&D experiments, the AWAKE project is rather unique. Like all of CERN's experiments, AWAKE is a collaborative endeavour with institutes and organisations participating around the world. "But unlike fixed-target experiments, where the users take over once CERN has delivered the facility, in AWAKE, the synchronised proton, electron and laser beams provided by CERN are an integral part of the experiment," explains Edda Gschwendtner, CERN AWAKE project leader. "So, of course, CERN's involvement in the project goes well beyond providing infrastructure and services."
Preparations are already underway, as CERN teams set out this summer to remake the CNGS area into a home for AWAKE. "We have removed part of the proton beamline and cleared the area upstream of the CNGS target to make way for the AWAKE installation, including a laser and 10 metre plasma cell," explains Edda. "CNGS's area downstream of the target, however, has been left untouched. As it is radioactive, we constructed a new shielding wall in July so that the AWAKE facility upstream can be a safe, supervised working area for users."
The AWAKE facility will also feature a clean room for the laser, a dedicated area for the electron source and two new tunnels for two new beamlines: one small tunnel to hold the laser beam (which ionises the plasma and seeds the wakefields); and a second, larger tunnel that will be home to the electron beamline (the "witness beam" accelerated by the plasma). These new tunnels are currently being carved out for the facility (see image).
While these works are ongoing, the AWAKE team at the Max Planck Institute for Physics in Munich is preparing to move both equipment and know-how to CERN. "In Munich, we are working with a 3-metre prototype of the plasma cell," says Allen Caldwell, AWAKE Spokesperson. "Our focus is on the science: learning the properties of the plasma cell as well as possible before we start with the 'real thing'. For example, we need to ensure that the temperature of the plasma in the cell is uniform and that the laser induces reliable wakefields."
"In addition to this, we are also addressing a number of hardware issues," adds Patric Muggli, AWAKE Physics and Experiment Coordinator. "For example, we are creating valves that allow the laser, proton and electron beams to enter the plasma cell. These need to be extremely fast but also durable, opening and closing an unprecedented 40,000 times in their lifetime."
Although new technology is being created for AWAKE, the experiment also re-uses existing equipment from CNGS and other CERN facilities: "The CLIC/CTF3 collaboration has agreed to provide their PHIN electron source and their expertise for the AWAKE facility, in addition to a number of klystron elements for the electron source," says Allen. However, modifying the PHIN electron source to fit the needs of AWAKE will require considerable work from CERN staff and collaboration members.
The experiment will be conducted in two phases, the first starting in 2016. "We first need to prove that the plasma cell is creating accelerating wakefields, showing that the self modulation is working and can be controlled," concludes Edda. "Once we have studied this phenomenon in detail, we will then use the wakefields to accelerate the electron witness beam. This will take us up to LS2, by which time we hope to have a good assessment of the potential of proton-driven plasma acceleration."
