The multipactor effect in rectangular waveguides
The multipactor effect is studied at length in rectangular waveguide geometries akin to WR-284. A test section utilizing a plug and play method was designed and implemented in order to carry out measurements with multiple test gaps. While many studies implement the use of global detection methods, usually in the form of phase and/or power monitoring, this test cell utilizes both local and global detection methods. An electron multiplier tube is used as the local detection method in order to view electron multiplication events with ns resolution in order to better understand the effects multipactor has on high Q structures. Multipactor was measured at 2.85 GHz with input powers fed into the test section ranging from single kW to MW. Measurements are reported for 'as processed' copper samples, as well as said samples undergoing an in situ bakeout. Comparison of measurements post bakeout coincided with literature in the desorption of surface contaminants contributing to an increase in secondary electron yield fi rst crossover point as compared to its 'as processed' counterpart. While lower thresholds for the multipactor effect were found for the samples, the reported data suggests that there is no theoretical upper limit in rectangular waveguide geometries due to the propagating modes electric fi eld distribution. As power was increased far past the requirements for first order multipactor, a temporal separation of the forward power detuning signal from the electron growth signal was observed, suggesting that at high power levels multipactor conducive regions shift towards the broadside walls of the waveguide, due to the field distribution of the dominant TE10 mode.
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