Image courtesy of Roy Kaltschmidt, LBNL
The BELLA laser during construction. In the foreground, units of the front end stretch and amplify short, relatively weak laser pulses before further amplification in the long central chamber. Amplification is done by titanium sapphire crystals boosted by a dozen pump lasers. At the far end of the hall the now highly energetic stretched pulse is compressed before being directed to BELLA’s electron-beam accelerator component.
On July 20, 2012, the laser system of the Berkeley Lab Laser Accelerator (BELLA) set a new world record by delivering more than one petawatt of power in a single pulse at a pulse rate of one hertz. Other lasers have produced more powerful pulses before but none has had the capability to produce subsequent pulses with a one-second turnaround time.
The laser’s peak power will be harnessed to accelerate electrons to new energies via the technique known as laser plasma wakefield acceleration. Unlike conventional particle accelerators that use RF fields to accelerate charged particles over long distances, the plasma wakefield technique uses large electric fields generated within plasmas to accelerate charged particles to high energies over much shorter distances. The high repetition rate combined with the high power of each pulse will allow users to perform critical experiments to optimize laser plasma acceleration and make it a viable method for particle acceleration.
Because BELLA’s laser has such high power and a high repetition rate, it will allow users to optimize the system in ways that can’t be done with lasers that fire a single shot a few times a day, which means that producing 10 GeV electrons is well within BELLA’s grasp. And because BELLA’s power and repetition rate are so high, a new door will open that will allow experiments with laser plasma wakefield acceleration to proceed with better controls and at a faster rate. The stage is set for the future development of compact particle accelerators for high energy physics and table-top free electron lasers to investigate materials and biological systems.
Basic research: Office of Science High Energy Physics program