From: James Ganong (JGanong@webtv.net)
Date: Fri Jul 28 2000 - 04:53:53 MDT
[Non-member submission]
Space-borne protective energy systems, like the deflector shields on the
fictional starship U.S.S. Voyager, are on the drawing board of
real-world scientists.
These "cold plasmas" -- analogs to the sophisticated defensive grids
envisioned by Star Trek's creators -- are ambient-temperature, ionized
gases related to those found deep within the sun's core.
Such plasmas are capable of shielding satellites and other spacecraft;
or making them invisible to radars; or both. Nor will they fry
electronics or melt metal.
On Earth, cold plasmas should permit rapid, room-temperature
sterilization of food, medical equipment and contaminated civilian and
military gear. Low-temperature plasmas could one day also make possible
an entire new generation of miniature lasers and ultra-low-energy
fluorescent light tubes.
While scientists have known of low-temperature plasmas since at least
the end of the 19th century, only within the past several years have
techniques emerged to make cold plasma generation practical.
Vaulting to the first ranks of cold-plasma research in the last three
years has been soft-spoken, unassuming Tunisian native Mounir Laroussi,
an electrical and computer engineer at Old Dominion University in
Norfolk, Va. Research groups at Stanford, Princeton, Ohio State,
Wisconsin and New York Polytechnic also are conducting their own
plasma-research programs.
Laroussi has literally put plasma on the table: devising an apparatus
that creates a mini-plasma inside a plexiglass cube by passing an
electric current through helium gas via specially calibrated electrodes.
Laroussi's process, specified in pending patent applications, is
scalable; cold-plasma containers of virtually any size are feasible. No
vacuum pumps are required, since the plasma is generated at normal
atmospheric pressure.
"Mounir is on the forefront. He's one of the pioneers," said Igor
Alexeff, president of the Institute of Electrical and Electronics
Engineer's Nuclear and Plasma Sciences Society and professor emeritus of
electrical engineering at the University of Tennessee in Knoxville.
"He's pushing very hard to develop a variety of practical plasmas. His
work is pretty impressive."
Invulnerable and invisible
The U.S. Air Force allocates some $10 million a year for research geared
toward satellite protection. Of that amount, $2 million is dedicated to
low-temperature plasma studies.
Robert Barker, program manager for plasma physics in the Air Force's
Office of Scientific Research in Arlington, Va. is so taken with
Laroussi's approach that he thus far has funneled $250,000 into
Laroussi's research since his arrival at Old Dominion from the
University of Tennessee a little over a year ago. The Air Force has
supported Laroussi's work since 1996.
Barker is drawn not just by Laroussi's plasma-creating prowess, but his
ability to make low-temperature plasma inexpensively, in bulk and
without the need for hulking equipment.
"What's intriguing about Mounir's work is the large volumes of plasma
he's been able to generate," Barker said. "He's making very good
progress in keeping costs and weight low. His approach gives the best
power figures for practical, large-volume generation of cold plasma we
have to date."
Power-hungry plasmas
Poke a finger inside Laroussi's tabletop plasma-generating apparatus and
all you'll get from the bluish, pilot-light-like ionized gas is a slight
tingle. But the harmless sensation is misleading, since it doesn't give
a complete picture of plasma's power. Depending on how a plasma is
"tuned," or how it is made more dense by increasing its frequency, it
could ward off microwave bursts and discharges from ground-based,
energized sources of potential damage and disruption.
Swirling in and around one another, a plasma's charged particles
interact constantly, giving rise to localized attractions or repulsions.
External energy splashing against the plasma --- say, from a potentially
disabling, concentrated burst of microwaves, or perhaps even from
certain varieties of particle-beam weapons fired from military bases on
Earth --- could be caught up within the plasma's complex electromagnetic
fields and dissipated completely or deflected into space.
Hotter plasmas, while dense, don't appear immediately practical as a
defensive shield because of destructive temperatures and high power
requirements. In theory, cold plasmas can be made more dense, but like
their hotter kin will demand more power. Energy availability and weight
--- the larger the required wattage, the heavier the equipment --- would
remain thorny issues.
"In theory, a plasma could deflect a particle beam or laser attack,"
Laroussi says. "It depends on what you're shooting at it and how high
you can tune the plasma frequency. That doesn't mean it's easy or
practically achievable, particularly with a cold plasma. It's a tough
requirement to meet at present."
Cloaking mirrors
A nearer-term application is cloaking. With the proper adjustments, a
plasma can be made into a kind of energy mirror, reflecting back or away
incoming electromagnetic waves, such as those emitted from ground-based
radars. In essence, any spacecraft outfitted with this kind of plasma
field would be completely cloaked from the probing attentions of radar
operators.
"The idea is to deflect or absorb the energy completely," Laroussi said.
"If you absorb the energy --- completely dissipating it within the
plasma --- the radar doesn't see anything. Nothing reflects back."
Light but potent
Lofting payloads into space must currently observe one of the Space
Age's key commandants: Make nothing so heavy that it must cost much to
launch.
Any on-board plasma-generation equipment would therefore have to be
small and lightweight. Laroussi's gear seems to fit the bill: compact
enough to save on weight, yet powerful enough to produce the necessary
plasma volume.
But don't expect completely impervious shields anytime soon. Any number
of technical issues remains to be solved, not the least of which is
exactly how to make cold plasmas dense enough to withstand attack. The
ultimate --- protection against projectiles or lasers --- is likely
decades away, at best.
"Ablative shields made of solid material might work," said the Air
Force's Barker. "A portion of the solid would be converted to plasma
[when hit]. But In a strict sense, I don't consider that plasma
shielding."
Star wars defense
Less immediately space-like, but no less practical, are biological
applications. Cold plasmas allow for rapid decontamination of clothing,
equipment or personal gear. In disrupting the integrity of cell
membranes, the plasmas appear to offer a rapid, simple and inexpensive
means of destroying even the hardiest bacterial spores. At present,
sterilization time can run hours; use of a cold plasma could sanitize in
mere minutes.
Should this application pan out, it could offer to hospitals and armies
alike a safe and reliable way to counteract potential health hazards,
either those posed by disease or in combat. Likewise, exobiologists
might rest easy knowing that cold plasmas could remove the potential
threat of contamination from collected interplanetary samples returned
to Earth's surface.
Still, it's hard to vanquish all the SF combat scenarios. Plasmas may be
one of the best defensive options as offensive capabilities continue a
rapid and relentless advance.
"This Star Wars stuff is coming," said Igor Alexeff. "Laser and
high-power microwave weapons are on the way; they're almost here. Lasers
are fierce weapons. To protect against them, you'd need a very dense
plasma, almost a solid. But a good cold plasma could really help out by
reflecting or absorbing energy from a microwave war weapon."
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