Preparation of Large-sized Low Loss Diamond Disks and Microwave Window Welding
Large-sized low loss diamond disks for long pulse high-power gyrotron are developed by DC arc plasma jet chemical vapor deposition.The diamond disks are welded through surface metallization and brazing process.Key performance parameters such as dielectric loss,thermal conductivity,surface flatness,and rough-ness are characterized by Fabry Perot open excitation cavity,laser thermal conductivity meter,3D profilometer,laser interferometer,etc.The vacuum sealability and microwave absorption property of the windows are tested by helium mass spectrometer leak detector and high-power long pulse microwave testing platform,respectively.The results show that the diamond disks with polished thickness of 1.36 mm have high dimensional accuracy with ther-mal conductivity of 17.9-18.7 W·cm-1·K-1.The dielectric loss tan8 of waveguide window is 1.76 × 10-4,and the dielectric loss tanδ of gyrotron window is 2.6 × 10-4.The calculation results indicate that with a microwave input power of 1 MW,the waveguide window loss power is about 2.34 kW,and the thermal stress at the center of the window is within the safe range.Under this power loss conditions,the gyrotron window can withstand an output power of at least 680 kW.
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