1 October 1991 Surface melting at ceramic windows due to high-power millimeter waves
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Proceedings Volume 1576, 16th International Conference on Infrared and Millimeter Waves; 15766D (1991) https://doi.org/10.1117/12.2297942
Event: 16th International Conference on Infrared and Millimeter Waves, 1991, Lausanne, Switzerland
Abstract
A mechanism limiting the lifetime of high-power millimeter wave windows is the degradation of the ceramic which is exposed to gas. We first observed this phenomena on the air side (atmospheric pressure) of a plane circular waveguide window (Al2O3 ceramic, ∅ = 70 mm) of a TE0,3 mode gyrotron, which was operated with a series of 100 ms pulses at a power of about 100 kW [1]. This degradation occured at the center of the window in an almost circular symmetry. Figure 1 shows the damage pattern at the time of first observation. It consisted of several thin concentric circles (width ≈ 0.3 mm, diameter ≈ 0.5, 2.5, 4.6, 6.7, 8.8 mm) which where not completely closed. From their radial location and from the window thickness one may conclude a TE0ln (or TM0,n) mode with n ≈ 19 being involved in the damage process. It is also observed that the circles occur only near the inner maximum of the TE0,3 mode power density. With further operation of the gyrotron the damage grew, the fine structure smeared out, and the resulting pattern approximately corresponded to the inner maximum of the TE0,3 mode power density (Figure 2).
© (1991) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
H.-U. Nickel, H.-U. Nickel, } "Surface melting at ceramic windows due to high-power millimeter waves", Proc. SPIE 1576, 16th International Conference on Infrared and Millimeter Waves, 15766D (1 October 1991); doi: 10.1117/12.2297942; https://doi.org/10.1117/12.2297942
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