Using Einstein's theory of special relativity to speedup
computer simulations, scientists have designed laser-plasma
accelerators with energies of 10 billion electron volts (GeV) and
beyond. These systems, which have not been simulated in detail
until now, could in the future serve as a compact new technology
for particle colliders and energetic light sources.
Researchers at Instituto Superior Técnico of Portugal
(IST), the University of California at Los Angeles (UCLA), and the
U.S. Department of Energy's Lawrence Berkeley National Laboratory
(Berkeley Lab) used Einstein's principle that length and time
scales change with the speed of the observer (in this case, the
simulator) to incorporate otherwise intractable calculations into
the simulations required to design these novel accelerators.
High-energy particle accelerators are used in many areas of
science and technology, including fundamental physics exploration
and discovery, medical science, chemistry, biology, and material
science, among others. In the past couple of decades, a new concept
of acceleration based on laser (or particle beam) plasma
interactions has been demonstrated, with the potential to greatly
reduce the size and cost of the world's largest atom smashers and
to create very compact accelerators for a wide variety of
applications.
In a laser wakefield accelerator (LWFA), an intense, short laser
pulse is sent through a column of tenuous plasma, generating a wave
wake on which particles can surf to very high energies. The
acceleration gradients obtained are more than three orders of
magnitude higher than conventional radio-frequency accelerators. In
the last five years, LWFA experiments have produced electron beams
with energies from 100 million electron volts to 1 GeV within
millimeter to centimeter distances. At 1 GeV, an electron is
traveling at 99.99999 percent of the speed of light. The next
decade promises tremendous improvements as a new generation of more
powerful lasers becomes available, and the process becomes better
understood.
It is at this point that numerical simulations play a critical
role, not only to determine the optimal laser and plasma
parameters, but also as a tool to explore new concepts and
configurations. The challenge, however, is that accurate one-to-one
simulations of the next generation of laser wakefield experiments
are not easily possible: it would take more than one year to
perform a single simulation using standard techniques. The
difficulty arises from the necessity to resolve the laser
wavelength of about one micron (1 millionth of a meter) while
simulating a laser propagating through a plasma that can be several
meters long - distances that are more than six orders of magnitude
apart. To access this range of scales in reasonable computational
times, researchers have successfully used reduced models. These
models, however, cannot capture some of the physics required for
next-generation experiments.
Performing simulations in a frame of reference that moves close
to the speed of light makes simulations of next-generation
experiments possible. By Einstein's theory of special relativity,
the laser pulse will stretch and the plasma will contract, which
brings the scales of the two entities closer together. This means
that modeling an experiment in this "boosted frame" can be more
than 1,000 times faster than a simulation in the standard
"laboratory frame."
Using this technique, scientists at IST, UCLA, and LBNL are now
designing and simulating self-guided stages up to 12 GeV - and
externally guided and injected stages up to 50 GeV. These new kinds
of numerical experiments enable the scientists to understand the
new physical processes involved, to optimize experimental
parameters, and to estimate the acceleration possible with the next
generation of laser systems. The new results show that laser
wakefield acceleration with near term lasers could lead to compact,
less expensive infrastructures for fundamental science research,
for new accelerator technology development, and might potentially
lead to a future particle collider at very high energies.
SOURCE