Plasma window
From Wikipedia, the free encyclopedia
The plasma window (also plasma shield,[1]) is a technology that fills a volume of space with plasma confined by a magnetic field. With current technology, this volume is quite small and the plasma is generated as a flat plane inside a cylindrical space.
Plasma is any gas that has had all of its particles (atoms or molecules) ionized and is generally held to be a separate phase of matter. This is most commonly achieved by heating the gas to extremely high temperatures although other forms of plasma are also possible. (See Plasma.) Plasma becomes increasingly viscous (thick) at higher temperatures, to the point where other matter has trouble passing through.
A plasma window's viscosity allows it to separate air at standard atmospheric pressure from a total vacuum. At the same time, the plasma window will allow radiation such as lasers and electron beams to pass. This property is the key to the plasma window's usefulness — the technology of the plasma window permits for radiation that can only be generated in a vacuum to be applied to objects in an atmosphere.
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[edit] History
The Plasma Window was invented at Brookhaven National Laboratory by Ady Hershcovitch and patented in 1995. [2]
Further inventions using this principle include the Plasma Valve in 1996. [3]
[edit] Plasma Valve
A related technology is the plasma valve, invented shortly after the plasma window. A plasma valve is a layer of gas in the shell of a particle accelerator. The ring of a particle accelerator contains a vacuum, and ordinarily a breach of this vacuum is disastrous. If, however, an accelerator equipped with plasma valve technology breaches, the gas layer is ionized within a nanosecond, creating a seal that prevents the accelerator's decompression. This gives researchers time to shut off the particle beam in the accelerator and slowly decompress the accelerator ring to avoid damage.
[edit] Properties
The physical properties of the plasma window vary depending on application, but so far most have been generated at temperatures around 15,000 kelvins (ref. Patent) [4]
The only limit to the size of the plasma window are current energy limitations as generating the window consumes around 20 kW per inch (8 kW/cm) in the diameter of a round window.
The plasma window emits a bright glow, with the color being dependent on the gas used.
[edit] Application
The most important application for the plasma window at the turn of the 21st century is as a lens that can pass energy but enforce a strict boundary between atmosphere and vacuum. This attribute of the plasma window enables the design of new types of advanced radiation sources and makes existing radiation sources cheaper to use.
At present, electron beam welding and melting are industrial processes that are superior, in many situations, to various alternatives, but too expensive to deploy for most projects. The original expense of electron beam technology was due to the lack of an efficient means for separating a vacuum, in which an electron source can operate, from atmosphere. The plasma window, by easily separating air from vacuum but still passing electrons, enables metals to be welded at atmospheric pressure. The only vacuum required is the small tube wherein the electron beam is generated. Without the plasma window, a large, expensive vacuum chamber would be required to hold all the parts being machined.
The plasma window also has important applications in scientific research, where it reduces the expense of exotic radiation sources.
[edit] Star Trek
Adherents of the science fiction television series Star Trek, and to a lesser extent fans of other sci-fi literature, viewed the announcement of the plasma window with an excited fervor. This is because the plasma window is exceedingly similar to the force field, a fictional technology which is a mainstay in science fiction in general and Star Trek in particular.
In fact with enough energy, a plasma window could be erected that would stop (and then incinerate) any physical projectile fired towards it; however the amount of energy required is currently far beyond what we are capable of producing and the temperature of the plasma window would be so high that it might damage whatever it was protecting. The window would also allow lasers and other energy weapons to pass unhindered.
Plasma windows also bear some resemblance to the force fields erected to keep the vacuum out of the hangar bays. Such a plasma window is theoretically possible if enough energy was available (also currently beyond our technology), and would even emit the same blue glow if argon was used to create the plasma. The biggest problem is that due to the extremely high temperatures, any space ship that passed through would be very badly damaged.
The parallels between Star Trek and the plasma window go even beyond its similarity to the force field. Star Trek's plots are littered with exotic particles and radiation that scientists use to manipulate and probe physical phenomena. The plasma window, with its extraordinary utility in enabling better, cheaper artificial sources for radiation, is a bright promise of a future where we are able to produce that plethora of particles as readily as the crew of the USS Enterprise.
[edit] Notes
[edit] External links
- Official article by Ady Hershcovitch - Inventor of the Plasma Window.
- BROOKHAVEN LAB WINS R&D 100 AWARD FOR THE "PLASMA WINDOW"
- Brookhaven National Laboratory - Where the Plasma Window was invented
- News on the Plasma Window
- Plasma Window Patent
- Plasma Valve Patent
- Acceleron LLC - specializes in electron beam welding
[edit] References
- Ady Herschcovitz (1995). High-pressure arcs as vacuum-atmosphere interface and plasma lens for nonvacuum electron beam welding machines, electron beam melting, and nonvacuum ion material modification, Journal of Applied Physics, 78(9): 5283-5288
- BNL Wins R&D 100 Award for `Plasma Window' [5]
- Ady Herschcovitz. Plasma Window Technology for Propagating Particle Beams and Radiation from Vacuum to Atmosphere. [6]
