Lawrence Berkeley National Lab physicists using one of the most powerful lasers in the world have accelerated electrons to the highest energies ever recorded from a compact accelerator – 4.25 billion electron volts (giga-electron volts or GeV).
A 9 cm-long capillary discharge waveguide used in BELLA experiments to generate 4.25-GeV electron beam. Image credit: Roy Kaltschmidt.
The record-breaking energies were achieved with the help of the Berkeley Lab Laser Accelerator (BELLA), which produces a quadrillion watts of power and began operation just in 2013.
The team, led by Dr Wim Leemans, sped up the particles inside a 9-cm long tube of plasma. The speed corresponded to an energy of 4.25 GeV.
The acceleration over such a short distance corresponds to an energy gradient a thousand times greater than traditional particle accelerators and marks a world record energy for laser-plasma accelerators.
“This result requires exquisite control over the laser and the plasma,” said Dr Leemans, who is the first author of a paper published in the journal Physical Review Letters.
Traditional particle accelerators, like CERN’s Large Hadron Collider, speed up particles by modulating electric fields inside a metal cavity. It’s a technique that has a limit of about 100 mega-electron volts per meter before the metal breaks down.
Laser-plasma accelerators take a completely different approach. In the case of this experiment, a pulse of laser light is injected into a short and thin straw-like tube that contains plasma.
The laser creates a channel through the plasma as well as waves that trap free electrons and accelerate them to high energies.
It’s similar to the way that a surfer gains speed when skimming down the face of a wave.
In order to accelerate electrons to even higher energies – the near-term goal is 10 Gev – Dr Leemans and his collaborators will need to more precisely control the density of the plasma channel through which the laser light flows. In essence, they need to create a tunnel for the light pulse that’s just the right shape to handle more-energetic electrons.
“Future work will demonstrate a new technique for plasma-channel shaping,” Dr Leemans said.
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W. P. Leemans et al. 2014. Multi-GeV Electron Beams from Capillary-Discharge-Guided Subpetawatt Laser Pulses in the Self-Trapping Regime. Phys. Rev. Lett. 113, 245002; doi: 10.1103/PhysRevLett.113.245002
