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Understanding Killer Electrons in Space (Forwarded)



 
 
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Old July 17th 07, 08:08 PM posted to sci.astro
Andrew Yee
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Default Understanding Killer Electrons in Space (Forwarded)

News and Communications Office
Los Alamos National Laboratory

Contact:
Nancy Ambrosiano, (505) 667-0471

July 10, 2007

Understanding Killer Electrons in Space

LOS ALAMOS, N.M. -- Los Alamos paper in Nature Physics solves mystery of
speeding particles

Settling a longstanding scientific debate, Los Alamos scientists have
demonstrated conclusively how electromagnetic waves accelerate ordinary
electrons in the belts of radiation outside Earth's atmosphere to a state
where they become "killer electrons," particles that are hazardous to
satellites, spacecraft, and astronauts.

Using data from several satellites, including NASA's Polar spacecraft, Los
Alamos scientists published in the July issue of Nature Physics a paper
showing how interactions between electromagnetic waves and electrons are
responsible for accelerating radiation-belt particles in the Van Allen
radiation belts to the point they become "killers."

The Van Allen radiation belts are doughnut-shaped regions encircling Earth
that contain high-energy electrons and ions trapped in Earth's magnetic
field.

The paper, "The Energization of Relativistic Electrons in the Outer Van
Allen Radiation Belt," was written by Yue Chen, Geoffrey D. Reeves, and
Reiner H.W. Friedel of the Laboratory's Space Science and Applications
group. "We're not the first people to look at these space-based density
gradients, but the essential achievement was coming up with the definitive
test," said Reeves.

Competing models had proposed various effects involving diffusion, each
roughly analogous to the ways piles of sand will spread out on a board
that's shaken. The Los Alamos team's paper provides the first analysis
that internal wave-particle acceleration is the only mechanism consistent
with observations for the majority of radiation belt enhancement events (a
surge of electrons up to 1,000 times more dense than they are in
storm-free conditions).

"Debates on the source of the acceleration have lasted for at least a
decade, and this paper finally settles the argument based on observations.
The result should be very useful for further radiation-belt research
work," Chen said.

The Los Alamos model involved measuring fluxes of electrons, counting how
many per second hit a satellite-borne detector, and converting the
physical measurements to magnetic coordinates. The results showed
localized peaks in intensity that could only be caused by acceleration of
those electrons by electromagnetic waves. "We know it's some kind of
interaction between the electromagnetic waves and the particles, but not
the exact mechanism. So it's a big step, but certainly not the only one in
understanding radiation belts," said Reeves.

The Los Alamos teams obtained differential electron flux data from the Los
Alamos energetic particle sensor (a burst-detector dosimeter) aboard a
Global Positioning System satellite, the Los Alamos Synchronous Orbit
Particle Analyzer (SOPA) aboard a geosynchronous orbit satellite, and the
Comprehensive Energetic Particle and Pitch Angle Distribution experiment
aboard NASA's Polar satellite.

The next big step in this field will be the planned 2012 launch of NASA's
two Radiation Belt Storm probes, part of the agency's "Living With a Star"
program to quantify the physical processes that generate the radiation
belts and cause them to decay. Observations from the two spacecraft will
enable the development of empirical and physics-based models for the
radiation belts. The empirical models will be used by engineers to design
radiation-hardened spacecraft, while the physics-based models will be used
by forecasters to predict geomagnetic storms and alert both astronauts and
spacecraft operators to potential hazards.

The paper is available online at
http://www.nature.com/nphys/journal/.../nphys655.html

Los Alamos National Laboratory is a multidisciplinary research institution
engaged in strategic science on behalf of national security. The
Laboratory is operated by a team composed of Bechtel National, the
University of California, BWX Technologies, and Washington Group
International for the Department of Energy's National Nuclear Security
Administration.

Los Alamos enhances national security by ensuring the safety and
reliability of the U.S. nuclear stockpile, developing technologies to
reduce threats from weapons of mass destruction, and solving problems
related to energy, environment, infrastructure, health and global security
concerns.

Related Links

* NASA killer electron site
http://www.nasa.gov/vision/universe/...electrons.html
* NASA's Polar Mission site
http://pwg.gsfc.nasa.gov/polar/


 




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