The breakdown at the dielectric window of the high-power microwave (HPM) horn limits the maximum radiation power of HPM system, and keeps the bottle neck of the development of the HPM technology in decades. In this paper, the multi-way diagnostics for the window breakdown at vacuum/dielectric interface are studied in the C-band multi-gigawatt HPM experiment with the atmospheric pressure SF6 environment. The method of using the fluorinated periodic surface is demonstrated to significantly improve the power capacity by fourfold, compared with the flat surface. The threshold for fluorinated periodic surface could be higher than 70 kV/cm for HPM with the frequency 4.3 GHz, and 40 ns pulse width.
The surface breakdown of dielectric windows seriously limits the transmission of high power microwaves (HPM), and has blocked the development of microwave technology in recent decades. In this paper, X-band HPM experiments of window breakdown at the vacuum/dielectric interface and the atmosphere/dielectric interface at single and repetitive pulses were conducted. The cross-linked polystyrene (CLPS) dielectric window with a periodic surface profile can significantly improve the breakdown threshold at single and repetitive pulses. Furthermore, the flat surface layer of CLPS was discovered to be carbonized to a depth of several millimeters and filled with electrical trees at repetitive pulses. Theoretical models were built to understand the underlying physics behind the phenomena in experiments. With the analysis of the electron resonance process breaking the molecular bond and the temperature rise caused by the traversing current in the dielectric material, a microscopic explanation for the carbonization of the dielectric window was introduced.
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