A Plasma Valve

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. (Brookhaven press release, May 28). A much faster, more complex version of a previously introduced "plasma window" (see New Scientist, 12 April 2003), the plasma valve is the latest example of novel uses of plasma for particle-beam applications; other recent ones include plasma acceleration of antimatter (Update 634), a plasma lens (Update 508), and plasma deflection of high-energy beams (Update 540).