Magnetic field shocklessly shoots pellets 20 times faster than rifle bullet – For orbiting satellites, equations of state, kinetic kill weapons

Media contact:

Neal Singer, nsinger@sandia.gov, (505) 845-7078

Technical contact:

Marcus Knudson, mdknuds@sandia.gov, (505) 845-7796

ALBUQUERQUE, N.M. — A magnetic field that accelerates pellets faster than
anything except a nuclear explosion has been developed experimentally at
the Department of Energy’s Sandia National Laboratories.

The machine that generates the field has been jokingly dubbed “the fastest
gun in the West,” but the description is an understatement.

“It’s the fastest gun in the world,” says Sandia physicist Marcus Knudson,
lead scientist on the project. The propulsion speed of 20 km/sec — almost
three times that necessary to escape the gravitational pull of the Earth
(about 7 km/sec) — would send material from New York to Boston in half a
minute, and from Albuquerque to Santa Fe in a few seconds. A rifle bullet
is typically propelled at 1 km/sec.

The machine, Sandia’s Z accelerator, currently propels dime-sized pellets
called flyer plates only a few hundred millimeters to gain information on
the effect of high-velocity impacts. The data gained can be used to simulate
the effect of flying space junk impacting the metal skin of an orbiting
observatory traveling in the opposite direction. The data is expected to
aid materials scientists trying to balance lightness against strength for
satellite and observatory shells.

The technique also has potential as a hypervelocity “kinetic kill” weapon
that, emanating from a lighter, more mobile source than the huge Z machine,
still could strike disabling blows through an adversary’s heavy armor. These
more mobile sources are already in development. Perhaps most importantly,
though least dramatically, the technique is the fastest, most accurate, and
cheapest method to determine how materials will react under high pressures
and temperatures. These characteristics can then be expressed in formulas
called “equations of state” — equations that tell researchers precisely
how materials will react if basic conditions like pressure and temperature
are changed by specific amounts.

While not a favorite topic for most people, accurate knowledge of equations
of state is essential for the U.S. to maintain its nuclear weapons without
physically testing them. The maintenance program, called “science-based
stockpile stewardship,” uses the most powerful computers in the world to
predict the result of unimaginably high temperatures and pressures upon
materials. Accurate predictions depend on accurate input about the
characteristics of those materials — that is, by a full knowledge of
their equations of state.

Researchers currently are unable to determine these material characteristics
except by the less accurate, more expensive methods of impacting test
materials with laser beams, or at lower energies with projectiles from
gas-powered guns.

The propulsion technique works by applying the Z machine’s 20 million amps
to produce an evolving magnetic field that expands in approximately 200
nanoseconds to reach several million atmospheres pressure. The relatively
gentle acceleration produced by the field is similar to that which might be
experienced in a smoothly rising high-speed elevator, rather than from the
shock imparted by a firearm.

Accelerated to 13 km/sec, the plates are neither distorted, melted, nor
vaporized, as they would be if shot from a gun. When the plate is
accelerated to a speed about 20 times faster than a bullet, or 20 km/sec,
the more forceful acceleration needed to reach higher velocity causes
temperatures of 2,500 K to occur in the flyer plate; this liquefies
aluminum flyer plates.

Better understanding of launch configurations is expected to eliminate this
problem, though liquidation still is superior to the worst alternative of
vaporization — the result if conventional acceleration could be used to
reach these speeds. (No power can be delivered from a vaporized pellet.)
Characteristics of copper and titanium plates are also being investigated.

The plates are accelerated in the vacuum chamber at the core of Sandia’s Z
machine, the most powerful producer of electrical discharge on Earth. Sandia
scientists last year used Z’s enormous magnetic field to test materials by
compressing them — a method called isentropic compression.

In this even newer technique, staggering the firing of Z’s 36 lines
eliminates the shock that melts the flyers at the higher velocities. The
resultant expansion of the powerful magnetic field is used to propel small
objects somewhat the way a surf boarder is propelled who catches one of a
succession of enormous waves.

A paper accepted by the Journal of Impact Engineering describes techniques
that accelerated the plates to 13 km/sec.

A paper to be submitted this spring to the Journal of Applied Physics shows
how improving the configuration of the loads increased the speed of the flyer
plates to 20 km/sec.

The work is funded primarily by DOE.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed
Martin Company, for the United States Department of Energy under contract
DE-AC04-94AL85000. With main facilities in Albuquerque, N.M., and Livermore,
Calif., Sandia has major research and development responsibilities in national
security, energy and environmental technologies, and economic competitiveness.

IMAGE CAPTION: [http://www.sandia.gov/media/NewsRel/NR2001/flyer.htm]

PENNIES FOR THE TOLLWAY? — Sandia researcher Mark Knudson holds two flyer
plates in his right hand and chambers of his high-tech gun in his left. In
the background is the innermost sanctum of Sandia’s Z accelerator, where a
rapidly expanding magnetic field drives pellets faster than any mechanism
on earth. (Photo by Randy Montoya)