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In this paper an impregnated cathode processing method for microwave tubes application is described. The methodology consists of three steps. In the first step is described is barium calcium aluminate preparation, the cathode tungsten porous manufacturing and the cathode impregnation. In the second step the cathode test vehicle is described and the final step, the cathode characterization is presented.
This paper describes the first stages in the development of an interaction circuit for a 12 kW X-band pulsed traveling wave tube. Requirements suggest a coupled-cavity slow wave structure is the best choice due to power handling, ease of manufacturing, and sufficient bandwidth. We present here the main features of the circuit and the cold model results as well. We are using mainly the HFSS 3D software...
In this work the design of a multiple-beam reentrant cavity with 6 beam tunnels for a 1.3 GHz klystron is presented. This cavity can be useful for a proton linac klystron including spallation neutron source applications. The study was carried out using the electromagnetic tool CST Microwave Studio.
This paper focus on an issue that vacuum electronics engineers face while designing wide band slow-wave structures for traveling wave tubes: The obtaining of reasonably flat gain curve over the bandwidth. It is usual to try a tradeoff between synchronism and interaction impedance profile in order to achieve a better gain response. We show here results from an in house one-dimensional large signal...
In this paper an experimental apparatus for impregnated dispenser cathode Auger spectroscopy is described. The apparatus consists of three ultra-high vacuum chambers, all connected by 6 inches gate valves. In the first vacuum chamber the cathode under test was assembled and there are some vacuum windows with electric feedthrough to bias to the cathode heater and anode. The temperature cathode surface...
The work functions of 5BaO.3CaO.Al2O3 porous tungsten dispenser cathodes were evaluated using practice work function technique of Miram to compare the coated and uncoated cathodes performance. Details of experimental apparatus used to measurement are presented and discussed.
A theoretical study, using power electronics tool simulation, is conducted to design an electronic power conditioner (EPC) to bias a traveling wave tube and its depressed collector stages. This study uses a parallel resonant DC-DC converter, which takes into account the parasitic capacitance of the high voltage transformer. It was possible to obtain 16 and 26 kV of output voltages with 1.8 kW of overall...
In this paper a dc design procedure of a X-band traveling-wave tube is described. This procedure consists in determine the geometry of the electron gun, the periodic permanent magnetic and the electron collector. It was found that an electron gun with a 0.26 µPerv, 9.1 kV, 225 mA and 0.6 mm beam radius without electrostatic beam control was suitable for this design. The PPM, constructed with samarium-cobalt...
The Ni-Mo composite alloy, to be used in microwave vacuum tube manufacturing, was prepared from metal powders previously homogenized, pressed and sintered at 1200°C by induction heating. The Ni-Mo sintered discs were annealed at 1150°C for 20min, and submitted to the roller process in 5 cycles to obtain a thin foil with 0.10 mm of thickness, for brazing process adopted to join the cathode components...
This paper presents a sequence of steps to begin the project of a cylindrical reentrant klystron cavity for 1.3 GHz. One analytical method and different CAD tools such as SUPERFISH and 3D eigenmode solver have been used for designing the cavity. The external coupling problem of the cavity is also discussed and is proposed a technique to get the critical coupling.
Impregnated thermionic cathodes production was the main objective of this work. The W-30wt.%Cu composite was sintered by induction heating (1200°C). The porous matrix was obtained after decopperization (1600°C). High purity Ba-Ca aluminate was impregnated (1630°C). The amount of aluminate impregnated was 18.32wt.%. Microstructure, porosity, and particle sizes distribution were determined.
W-Cu composites were used as starter materials of the thermionic cathode matrices for microwave tubes. However the decopperization affects their microstructure. An apparatus and an experimental procedure were developed to reduce the damages introduced during the decopperization. The matrix porosity (34.6%) was analyzed by SEM and its composition was determined by EDX.
In this work the design of multiple-beam reentrant cavities with 4, 6, and 8 beam tunnels for a 350 MHz is presented. These cavities can be useful in a multiple-beam klystron development for proton linac including spallation neutron source applications. The study was carried out using the electromagnetic tool CST Microwave Studio.
The synthesis of high purity barium calcium aluminate in oxidant atmosphere, without the pyrolysis step in hydrogen atmosphere, followed by the high energy ball milling to reduce the average particle size, was investigated to improve the impregnation process of the aluminate in porous tungsten matrices by induction heating.
To evaluate the computational time performance of three computational tools: EGUN2, XMGUN and CST, a 0.47μPerv, 1kV axis-symmetric gridless electron gun, working under the space charge-limited flow, was analyzed. It was observed, between the three codes, a good electric current agreement but the 2.5D codes presented better time responsive.
We derive analytic formulae for the electrostatic force between ring and disc charge distributions inside a grounded metallic pipe using the Green’s function technique. These distribution models are useful in the modeling of electron beams commonly employed in microwave tubes. We analyze the electric force between two discs, between two rings, and between a disc and a ring and we compare the results...
In this paper a design procedure of a 9kV, 0.45A, with a beam waist of 1.5 mm electron gun, without control grid, operating under the space-charge limited condition, to be used in a C-Band Traveling-Wave Tube (TWT), is presented. During the design, three electron gun geometric parameters were varied, namely: the cathode-anode distance, the anode height and the focusing electrode angle, in order to...
This paper presents some experimental results of unloaded Q-factor, Q0, measurements in klystron cavities using the critical points method. The circuit model and impedance locus involving this method are outlined in order to present the experimental procedure. The values calculated for a typical reentrant S-band klystrons cavity, using a vector network analyzer, were 3394 for the unloaded Q0, 1.2715...
In this paper a methodology to determine the suitable magnetic focusing properties that minimizes the electron beam ripple, propagating in a drift region, is presented. The methodology is applied in a typical C-band, power traveling-wave tube (TWT) which needs a 9.0 keV and 0.4 A electron beam with 0.8 mm of beam waist for a right operation. Using numerical simulation tools the beam behavior was investigated...
This paper describes the development of a microwave window for high power pulsed traveling-wave tubes for radar application. Given the operational frequency band, the window dielectric materials (beryllia or alumina), and the standard waveguide (WR-90), a tridimensional frequency domain solver was used to design the window geometry. We present here the effect of the window parameters and the experimental...
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