http://www.bnl.gov/bnlweb/pubaf/pr/2003/bn...bnlpr052803.htm A PLASMA VALVE, a device that uses electrically charged particles to
act as a barrier between air and vacuum, has been invented by a
Brookhaven-Argonne collaboration. These two DOE labs joined forces
to provide a needed component for Argonne's Advanced Photon Source
and similar facilities worldwide. Inside the walls of
accelerators, synchrotrons and storage rings, a good vacuum-empty
space mostly devoid of matter-enables particle beams to travel
unimpeded for hours. However, if a leak causes air to rush into the
vacuum, the particle beam spreads out and deposits its energy onto
surrounding walls, disrupting the beam and damaging valuable
equipment. The faster the leak can be closed, the less
damage will be done to the walls. The plasma valve, which has no
moving parts, can activate in a nanosecond, a million times faster
than mechanical valves. To keep air from rushing in, the
Brookhaven-Argonne team create a dense, high-temperature plasma
(collection of charged particles) held together by electric and
magnetic fields. Housed inside a hollow copper cylinder, the plasma
reaches a temperature of 15,000 degrees Kelvin (about 50 times
greater than room temperature)-making the plasma particles bounce
around so vigorously that they collide with air molecules and
prevent them from passing into the vacuum. Moreover, the valve's
confining electromagnetic fields prevent the plasma itself from
rushing into the vacuum.