Currently, methods of laser micromachining of various kinds of microsized structures are actively developed by scientists and engineers in a variety of fields. Particularly, laser micromachining allows for selective ablation of thin metal films on dielectric substrates in order to create planar conductive structures with rather complex patterns. Meander-like structures on dielectric substrates can serve as a slow-wave structure in perspective compact millimeter band vacuum electronic devices such as traveling-wave tubes. Thus, the aim of this work was to prepare conductive planar structures from thin metal coatings based on a copper-molybdenum alloy. Copper-molybdenum thin films were deposited onto dielectric substrates by magnetron co-sputtering. Then the coatings were micromachined using a nanosecond pulsed laser to form a series of planar structures in the shape of strips of varied width. Deposited coppermolybdenum thin films after laser micromachining suffer from lack of adhesion to the substrates. Possible way to overcome this issue is use of an adhesion sublayer such as titanium or chromium.
Millimeter-band traveling-wave tubes with multiple electron beams have attracted an increasing interest thanks to higher output power. In this work, we report the results of the development of the technological approach to microfabrication of a meander-line slow-wave structure for millimeter-band traveling-wave tubes with multiple sheet electron beams. We used a precision CNC laser machine equipped with a 1064-nm pulsed YAG:Nd fiber laser maintaining regimes with the duration of laser pulses from 200 ns to 8 ns. Several SWS samples have been fabricated and studied by scanning electron and optical microscopy methods
Traveling-wave tubes (TWT) with microstrip planar slow wave structures (SWS) have attracted an increasing interest thanks to low operating voltage and size of the tube, as well as compatibility with modern microfabrication technologies. In this work, we report the results of design, fabrication, and experimental cold-test study of planar meander-line SWSs for millimeter-band TWTs (V-, W-, and D-band). SWS samples have been fabricated using the technology based on magnetron sputtering and subsequent laser ablation.
Gyrotrons are the most powerful radiation sources in sub-THz and THz bands, which are of great importance for many applications, such as electron-cyclotron plasma heating, DNP/NMR spectroscopy, plasma diagnostics, biomedical applications, etc. All of these applications require frequency-stable, single-mode operation. Apart from the traditional methods for frequency stabilization, several other approaches have attracted a considerable interest. In this paper, we present a review of recent studies aimed at deeper understanding of injection locking of a gyrotron by an external signal, as well as of self-injection locking by partial reflection of the output power from a remote load. The increasing of frequency stability, expanding of the frequency tunability range, and the possibility of suppressing of the parasitic modes are discussed.
Design and preliminary numerical simulations of D-band planar microstrip meander-line slow wave structure for lowvoltage tubes with sheet electron beam were carried out. An original approach based on magnetron sputtering and laser ablation methods was utilized for microstrip meander-line slow wave structure microfarication. An application of nanosecond and picosecond laser ablation for microfabrication of D-band (110-170 GHz) planar microstrip meander-line slow wave structure was considered. We have verified our original approach for planar slow wave structures microfabrication by using different CNC precision laser machines operating with different values of laser pulse duration (100 ns, 8 ns, 4 ns and 10 ps). Samples of slow wave structures were fabricated and characterized by scanning electron microscopy and profilometry methods. It was shown that each considered CNC precision laser machine allows fabricating D-band microstrip meander-line slow wave structure with required dimensions, but picosecond laser ablation has such advantages as the absence of ablation products (droplets, and etc.) on the slow wave structure surface. As the next step, we are going to study S-parameters of microfabricated D-band microstrip meander-line slow wave structure samples experimentally by using vector network analyzer with D-band frequency converters.
Microfabricated vacuum power amplifiers and oscillators operating at millimeter and submillimeter (THz) bands are of great interest for applications in high-speed communication, radar, security and military systems, electronic warfare, etc. In this work, we report the results of numerical simulation and cold-test measurements of electromagnetic parameters of the V-band (50-70 GHz) planar meander-line SWS. The microstrip meander-line SWS is suitable for using in a millimeter-band TWT amplifiers. Several samples of copper microstrip meander-line SWS on a quartz substrate consisting of 50 meander periods with input and output couplers were designed, microfabricated and optimized. The SWS was microfabricated by using magnetron sputtering and laser ablation processes. This technique is a more facile, flexible and lower cost as compared to photolithography method. Transmission and reflection of proposed SWS were measured experimentally and calculated numerically. The results of the experimental cold-test measurements are verified by numerical simulations. Electromagnetic parameters of the SWSs were simulated using the finite-element ANSYS HFSS and COMSOL Multiphysics software packages. The results obtained with these two codes are in excellent agreement with each other and good agreement between experimental and numerical results is also observed.
Medium-power (10-100 W) THz-band gyrotrons operating in a continuous-wave (CW) mode are of great importance for many applications such as NMR spectroscopy with dynamic nuclear polarization (DNP/NMR), plasma diagnostics, nondestructive inspection, stand-off detection of radioactive materials, biomedical applications, etc. For all these applications, high frequency stability and tunability within 1-2 GHz frequency range is typically required. Apart from different existing techniques for frequency stabilization, phase locking has recently attracted strong interest. In this paper, we present the results of theoretical analysis and numerical simulation for several phase locking techniques: (a) phase locking by injection of the external driving signal; (b) mutual phase locking of two coupled gyrotrons; and (c) selfinjection locking by a wave reflected from the remote load.
Microfabricated vacuum-tube millimeter- and THz-band sources are of great interest for numerous applications such as communications, radar, sensors, imaging, etc. Recently, miniaturized sheet-beam traveling-wave tubes for sub-THz and THz operation have attracted a considerable interest. In this paper, we present the results of modeling and development of slow-wave structures (SWS) for medium power (10-100 W) traveling-wave tube (TWT) amplifiers and backwardwave oscillators (BWO) in near-THz frequency band. Different types of SWSs are considered, such as double-vane SWS for TWT with a sheet electron beam, a folded-waveguide SWS, and novel planar SWSs on dielectric substrates.
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