Upton, NY -- The U.S. Department of Energy's Brookhaven National Laboratory has won a 1996 R&D 100 Award for a novel device called a plasma window, which has several potential industrial and scientific applications. These include electron-beam welding; recovering scrap metal through electron-beam melting; using certain industrial processes for making new materials or modifying existing materials; and transmitting beams of radiation for experiments in advanced synchrotron light sources, scientific machines that use x-rays and ultraviolet light to probe materials.
R&D 100 Awards are given annually by Research and Development magazine to the top 100 technological achievements of the year. Typically, these are innovations that transform basic science into useful products.
The plasma window is an ionized gas, or a gas with charged particles confined by electric and magnetic fields, that, under special conditions, separates atmospheric pressure from a vacuum. Additionally, the device can focus charged particle beams, especially electron beams.
Brookhaven Lab physicist Ady Hershcovitch invented the plasma window, which is his second device to win an R&D 100 Award. In 1987, Dr. Hershcovitch won the award for developing an ion probe, a diagnostic device to be used in tokamak fusion reactors.
The plasma window, in which hot gas particles are trapped by electric and magnetic fields, prevents air from rushing into a vacuum chamber. At 12,000o Celsius (21,632oFarenheit), the plasma window is about 300 times as hot as the air at room temperature. This intense heat makes the ionized atoms and molecules move around faster and collide more often with air molecules, thus stopping most of them when they try to pass through the plasma window. Also, since the plasma window matches atmospheric pressure with only one-fortieth its density, less air pressure can escape from it into the vacuum, which is supposed to be devoid of pressure. (For a complete scientific discussion of the invention, see Dr. HershcovitchÌs paper in the November 1, 1995 edition of the Journal of Applied Physics.)
Electron-beam welding is used for piecing together metal parts
in airplanes, ships, scientific equipment and semiconductors.
Since existing nonvacuum electron-beam welders have dispersed
electron beams, they are not focused enough for high-quality welds
or to reach crevices. In-vacuum welding overcomes this problem,
but the vacuum system limits the size of the assemblies to be
welded. The plasma window facilitates high-quality, nonvacuum
electron-beam welding at production rates that are at least twice
as fast as in-vacuum welding. At an hourly operating cost of $150
for an electron-beam welder, production-cost savings would be
The plasma window can also aid in the operation of electron-beam
melting, a method frequently used to recover scrap metals from
recycled materials. The new invention effectively increases operating
pressure of the electron-beam furnace tenfold. High pressure in
the furnace prevents the evaporation of valuable metal alloys.
Ion implantation, dry etching and microfabrication are techniques
widely used by industry to make new materials or modify existing
ones. For example, they may be used for making patterns on semiconductors.
The plasma window has the potential to make these processes more
efficient, since it will allow them to be performed at atmospheric
pressure, rather than in a vacuum. This new possibility can cut
production expenses in half -- substantial savings at a typical
hourly cost of $250.
Plasma windows can also be used to transmit intense x-rays and
ultraviolet light from a vacuum to the atmosphere in advanced
light sources, where researchers use these forms of radiation
to probe materials. In intense light sources, there are difficulties
in using existing technologies, like beryllium windows, because
they absorb radiation and degrade the beam.
The development of the plasma window was made possible by a technology
maturation grant from the U.S. Department of Energy's Energy Research
Division and Laboratory Technology Program.
Brookhaven National Laboratory carries out basic and applied research
in physical, biomedical and environmental sciences and in selected
energy technologies. Associated Universities, Inc., a nonprofit
research management organization, operates the Laboratory under
contract with the U.S. Department of Energy.