Super-brief pulses for nuclear
2/11/2002 1:38 PM
BALTIMORE, Feb. 6 (UPI) -- Energy bursts lasting only
zeptoseconds -- among the briefest time spans theorized -- may
in principle grant scientists the power to look inside an atom
and control nuclear fusion.
"I'm not talking about exciting or suppressing atomic
explosions -- yet," said lead researcher Alexander Kaplan of
Johns Hopkins University in Baltimore. "But this could
possibly mean we could touch the nucleus -- and one of the
ultimate ideas would be trying to control nuclear reactions,
slow them down or the other way around."
These energy bursts and the unbelievably powerful magnetic
fields used to create them -- of a magnitude found normally
only in collapsed stars -- may in future help scientists do
anything from scan human bodies to generate experimental new
states of matter and investigate the origin of the cosmos.
"Zeptosecond pulses and astrophysical scale magnetic fields
would be a significant achievement," said laser expert Mike
Perry, director of the photonics division at General Atomics
in San Diego. "Any ability to perform astrophysical scale
experiments in the laboratory offers the promise to test
rapidly unfolding theories of the early universe."
The pulses and fields could theoretically be created by an
super-powerful laser-driven electron accelerator called a
"lasetron." This new application of existing technologies is
proposed by Kaplan and his colleague Peter Shkolnikov of the
State University of New York in Stonybook in the scientific
journal Physical Review Letters.
In theory, a lasetron requires a petawatt laser, which can
deliver laser beams that pack a quadrillion-watt punch -- more
than 1,200 times the entire U.S. electrical generating
capacity -- in less than trillionths of a second. About three
petawatt lasers are currently under construction around the
world, and one once operated at Lawrence Livermore National
Laboratory in California under Perry's leadership.
A petawatt laser fired at wires only a few hundred atoms in
diameter -- the mightiest of hammers hitting the tiniest of
anvils -- could drive the electrons in those targets to
incredibly near-light speeds. These electrons are actually 100
times more massive than electrons at rest, because kinetic
energy actually transforms into mass at such
Kaplan and Shkolnivov theorize a circularly polarized
petawatt laser beam -- one in which all the light rays are
aligned to move circularly -- would cause electrons it hit to
spin in extremely tight orbits only 3,000 angstroms in
diameter, or roughly 3,000 times the diameter of a hydrogen
A rotating electrical charge creates a magnetic field and
these electrons would generate a magnetic field of about 1
million tesla, which is a far, far more powerful field than
any made on Earth so far.
"It's unbelievable," Kaplan said. "The best we can get in
the lab nowadays is a few hundred tesla, maybe 1,000 if we
were generous with fields developed by explosions ... This is
a magnetic field more powerful than any that normally exist in
the sun, and closer to the field found in a white dwarf."
This million-tesla field is powerful enough for the
electrons to bottle themselves into one huge electron, and
such bottled-up electrons fire energy bursts. The faster the
electrons go, the shorter the pulse, and in theory, these
electrons would generate bursts lasting only zeptoseconds.
Light can travel around the Earth in a tenth of a second --
but in a zeptosecond, light can only travel the distance of an
With zeptosecond pulses, it may be possible to look inside
a nucleus, "see almost a movie, look at internal nuclear
motion or a fast process like fusion or fission, or stimulate
and control nuclear reactions," Kaplan said. "It is possible
to start doing crazy things."
This experimental application may remain on the horizon for
a while -- no sensor is as yet sensitive enough to detect
zeptosecond pulses, and a million-tesla field would likely
blow out any detectors so far, Kaplan said. Perry added the
edges of a petawatt pulse could explosively vaporize its
target before the pulse's core drives the wire's electrons to
Still, Kaplan said weaker lasers could still generate
powerful fields for advanced magnetic scanners in an X-ray
emulating system "that would allow you to look into people at
an airport, for example."
"It's one of those wild shots that produce a whole chain of
ideas," Kaplan said.
(Reported by Charles Choi in New York.)
Copyright © 2002 United Press