A laser pulse traveling through a plasma accelerates free electrons in its wake
Berkeley Lab scientists are leading in a race to develop laser-based accelerator capable of zapping electron beams to energies exceeding 10 GeV in a distance of just one meter. Groups in the UK and France are working feverishly to best the record set by Leemans’ group in 2006. China has also deemed it a high-priority growth area.
In about four years, the Berkeley Lab Laser Accelerator, or BELLA, will demonstrate the promise of a novel and compact method of accelerating high-energy particles, by making use of a series of synchronized laser systems.
This group achieved a major breakthrough in 2006 when they broke the world record for laser-wakefield acceleration, a technique in which particles are accelerated by waves in plasma generated by intense pulses of laser light. In the wake of the laser pulse, electrons surf the waves of the ionized gas. Leemans and coworkers used this concept to accelerate electron beams to energies of more than 1 GeV in a distance of just 3.3 centimeters. Compare that to the Stanford Linear Accelerator Center, or SLAC, which takes 2 miles (3.2 kilometers) to boost electrons to 50 GeV.
Although the main purpose of the project is to develop a new generation of more compact accelerators for high energy physics research, laser plasma wakefield technology has several potential applications.
100 of the 10GeV accelerators could enable a 100 meter long teravolt accelerator.
A multi-GeV beam could be used to produce highly-collimated, high-energy photons that could penetrate cargo in a nondestructive way, allowing inspectors to remotely “see” inside a package, which would be highly useful for national security. BELLA could also be used to build free-electron lasers (FEL). Like all lasers, FELs emit energetic beams of light. But unlike conventional lasers, they operate on a different set of principles that make them highly tunable. Because of this property, free-electron lasers can provide extraordinarily valuable tools for materials scientists, chemists, biologists, and researchers in various fields working on problems in fundamental energy research, allowing them to probe ultrashort, nanoscale phenomena. Their tunability also makes them useful for medical diagnosis.
Finally, with some modification, BELLA could produce a narrow bandwidth x-ray beam that could be used to take very high-resolution x-ray images for medical use. If the laser technology that drives the laser plasma accelerators keeps on improving by becoming less expensive and more compact, it could one day be an alternative to conventional x-ray machines, offering a new technique for better images with reduced x-ray dose.
Completing BELLA will require:
Completing BELLA will require a 1-Hz, 1-PW laser — the highest average power (40 W) petawatt-class laser in the world.
To achieve BELLA’s main objective of 10-GeV electrons, a new and much more powerful laser will have to be put in place, a state-of-the-art laser that can fire a 40-joule pulse in a brief 40 femtoseconds, then build up to fire again and again, once every second, a repetition rate of one hertz (1 Hz). Such a laser will have an average power of 40 W and a peak power of a quadrillion watts — a petawatt, 1 PW.
“Since the time we designed and built the LOASIS 40-TW laser ourselves, there has been a revolution in the field of laser technology,” Leemans says. “Advances are now driven by commercial companies, and by military requirements, and we have been talking with two companies who want to build a laser for BELLA under our supervision.”
Plasma Accleration at wikipedia