On the night of July 20, 2012, the laser system of the Berkeley Lab Laser Accelerator (BELLA), which is nearing completion at the Lawrence Berkeley National Laboratory, delivered a petawatt of power in a pulse just 40 femtoseconds long at a pulse rate of one hertz – one pulse every second. A petawatt is 10^15 watts, a quadrillion watts, and a femtosecond is 10^-15 second, a quadrillionth of a second. No other laser system has achieved this peak power at this rapid pulse rate.
"This represents a new
world record," said Wim Leemans of Berkeley Lab's Accelerator and Fusion
Research Division (AFRD) when announcing the late-night success to his
team. Leemans heads AFRD's Lasers and Optical Accelerator Systems
Integrated Studies program (LOASIS) and conceived BELLA in 2006.
"My congratulations to the BELLA team for this early mark of success,"
said Berkeley Lab Director Paul Alivisatos. "This is encouraging
progress toward a future generation of smaller and far more efficient
accelerators to maintain our nation's leadership in the tools of basic
"Congratulations to all of you on this spectacular achievement," said
Stephen Gourlay, Director of AFRD. "It doesn't seem that long ago that
BELLA was just a dream, and now there is even more to look forward to.
Thank you all for the hard work and support that made this a reality."
Leemans says, "BELLA will be an exceptional tool for advancing the
physics of laser and matter interactions. The laser's peak power will
give us access to new regimes, such as developing compact particle
accelerators for high-energy physics, and tabletop free electron lasers
for investigating materials and biological systems. As we investigate
these new regimes, the laser's repetition rate of one pulse per second
will allow us to do 'science with error bars' – repeated experiments
within a reasonable time."
The BELLA design draws on years of laser plasma accelerator research
conducted by LOASIS. Unlike conventional accelerators that use modulated
electric fields to accelerate charged particles such as protons and
electrons, laser plasma accelerators generate waves of electron density
that move through a plasma, using laser beams to either heat and drill
through a plume of gas or driving through plasma enclosed in a thin
capillary in a crystalline block like sapphire. The waves trap some of
the plasma's free electrons and accelerate them to very high energies
within very short lengths, as if the accelerated electrons were surfing
on the near-light-speed wave.
LOASIS reported its first
high-quality electron beams of 100 million electron volts (100 MeV) in
2004 and the first beams of a billion electron volts (1 GeV) in 2006 –
in a sapphire block just 3.3 centimeters long. Planning for BELLA began
The BELLA laser is expected to drive what will be the first laser plasma
accelerator to produce a beam of electrons with an energy of 10 billion
electron volts (10 GeV). Before being converted to other uses, the
Stanford Linear Accelerator Center achieved 50 GeV electron beams with
traditional technology, but required a linear accelerator two miles long
to do it. By contrast, the BELLA accelerator is just one meter long,
supported by its laser system in an adjacent room.
"LOASIS know-how in assembling our own laser systems allowed us to
specify the laser requirements and specifications we'd need to achieve
reliable, stable, tunable 10 GeV beams with short warm-up time," Leemans
says. "U.S. Secretary of Energy Steven Chu said that new tools lead to
new science, the kind BELLA is specifically designed to do. "
The BELLA laser system has already demonstrated compressed output energy
of 42.4 joules in about 40 femtoseconds at 1 Hz. Its initial peak power
of one petawatt is twice that of lasers recently said to produce pulses
more powerful than that consumed by the entire U.S. "at any instant in
time." "Instant" is the operative word, since the BELLA laser's average
power is just 42.4 watts, about what a typical household light bulb
uses. The enormous peak power results from compressing that modest
average power into an extremely short pulse.
Developed by Thales of France, whose team at Berkeley Lab was led by
Francois Lureau, and installed in facilities constructed at Berkeley
Lab, the BELLA laser system is fully integrated with Berkeley Lab
equipment and personnel protection systems. It is expected to rapidly
improve upon its first record-breaking performance and will soon be able
to deliver the powerful pulses needed to create
10-billion-electron-volt electron beams in an accelerator just one meter
long. Experiments to demonstrate BELLA's ability to attain 10-GeV beams
will begin this fall.