The future of particle acceleration has begun. Awake is a promising concept for a completely new method with which particles can be accelerated even over short distances. The basis is a plasma wave which accelerates the electrons and thus brings them to high energies. A team led by the Max Planck Institute for Physics is now reporting progress in this context. For the first time, they were able to accurately time the production of the proton microbunches that drive the wave into the plasma. This fulfills an important prerequisite for the use of Awake technology for collision experiments.
How to create an electron wave? The carrier substance for this is a plasma (i.e. an ionized gas in which the positive and negative charges are separated). Directing a beam of protons through the plasma creates a wave on which electrons rise and are accelerated to high energies.
Awake’s proton source is CERN’s SPS ring, a pre-accelerator for the 27-kilometer circumferential ring of the Large Hadron Collider (LHC). It produces bunches of protons about 10 cm long. “However, to generate a high amplitude plasma wave, the length of the proton beam has to be much shorter – on the order of a millimeter,” explains Fabian Batsch, a doctoral student at the Max Planck Institute for Physics.
Scientists take advantage of self-modulation, a “natural” interaction between the bouquet and the plasma. “In the process, the longest proton bundle is split into high-energy proton microbunches only a few millimeters in length, building the beam of the train,” Batsch explains. “This process forms a plasma wave, which propagates with the train traveling through the plasma field.”
Precise timing allows ideal acceleration of electrons
However, a stable and reproducible field is needed to accelerate the electrons and cause them to collide. This is exactly what the team has found a solution for at the moment. “If a sufficiently large electric field is applied when the long bunch of protons are injected and the self-modulation is thus immediately set in motion.”
“Since plasma forms right away, we can accurately time the phase of short proton microbunches,” says Patric Muggli, head of the Awake working group at the Max Planck Institute for Physics. “This allows us to set the pace for the train. So the electrons are captured and accelerated by the wave at the perfect time.”
First research projects in sight
Awake technology is still in the early stages of development. However, with each step towards success, the chances that this accelerator technology will actually be used in the decades to come increases. The first proposals for smaller accelerator projects (for example to study the fine structure of protons) must be made as early as 2024.
According to Muggli, the advantages of the new accelerator technology – the acceleration of the plasma wake field – are obvious: “With this technology, we can reduce the distance needed to accelerate electrons to the maximum energy of a. factor 20. The accelerators of the future could therefore be much smaller. This means: less space, less effort and therefore lower costs. “
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