**4.5 High power output window**

The millimeter-wave signal is finally taken out of the gyrotron with the help of the high-power output window. This window consists of a ceramic disc which isolates the ultra-high vacuum environment inside the gyrotron enclosure from the outside

*Gyrotron: The Most Suitable Millimeter-Wave Source for Heating of Plasma in Tokamak DOI: http://dx.doi.org/10.5772/intechopen.98857*

**Figure 10.** *Cut section view of a beam tunnel.*

**Figure 11.** *A typical QOL for converting TE6,2 cavity mode to Gaussian mode.*

atmosphere. The ceramic disc material and thickness is so chosen that it appears almost transparent to the electromagnetic-wave and the millimeter-wave comes out of the gyrotron through the window with minimum attenuation. Also, a material, which is a good thermal conductor but bad electrical conductor, is chosen for window. Usually single disc window is used. However, for the purpose of VSWR matching, sometime double disc window may be incorporated. For short-pulse operation, sapphire, beryllium-oxide (BeO) or boron-nitride may be used as window ceramic materials. For long pulse high-power operation, chemical vapor deposition (CVD)

**Figure 12.** *Cut-section view of a typical collector.*

diamond is generally used as the window material due to its very high thermal conductivity.
