Accelerator: Waveguide http://www2.slac.stanford.edu/vvc/accelerators/waveguide.html
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Waveguide
A waveguide is an evacuated rectangular copper pipe. It carries
electromagnetic waves from one place to another without significant loss in intensity . This is in contrast to waves broadcast from any antenna, which lose intensity because they spread out over a large volume.
The size of the waveguide must be a multiple of the wavelength of the wave, so waveguides are only practical for electromagnetic waves in the microwave range, with wavelengths on the scale of a few centimeters.
How does a waveguide work?
If a microwave oscillation is set up at one end of a waveguide, its electric fields cause electric currents to flow in the copper walls. These currents in turn induce new electric and magnetic fields in the waveguide, oscillating with the same frequency as the original microwave. The net effect is that the microwave travels along the pipe. There is some small loss of energy due to the electrical resistance of the copper, but the microwave intensity that arrives at the far end of the pipe is almost as large as the intensity fed in at the beginning.
Accelerator: Waveguide http://www2.slac.stanford.edu/vvc/accelerators/waveguide.html
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Close-up view of part of a waveguide in the NLC Test Accelerator.
For the very high microwave intensities used at SLAC, the waveguide must be evacuated (placed under vacuum) because the intense electric fields would breakdown through lightning-like spark formation if air were present in the pipe. The waveguides at SLAC are kept at about 10-11 times atmospheric pressure. Such low air pressure is also called "high vacuum".
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