Yong Han

An Evaluation of Heat Dissipation Capability of Slow-Wave Structures

A new experimental evaluation method is presented for evaluating and comparing the heat dissipation capability of the slow-wave structures (SWSs) of helix traveling-wave tube (TWT). The practicality and simplicity of the evaluation method have been validated through experimental tests in some components with different assembling and processing methods, such as the cold stuffing, the heat shrink, the hot insertion, the molybdenum wrapping methods, and so on. Experimental results demonstrate that our evaluation method can be used effectively and conveniently to estimate and compare the thermal dissipation capability of the SWSs of the helix TWT

Thermal Analysis of a Helix TWT Slow-Wave Structure

A novel and effective analytical method using ANSYS has been developed for studying the heat-dissipation capability of a helix traveling-wave-tube slow-wave structure (SWS). This method, which is based on calibrating theoretical calculations with experimental data, is able to precisely predict the SWS heat dissipation, thereby reducing material costs and saving time. The consistency and feasibility of this method have been verified by experimental tests on SWSs using copper-plated helices and both BeO and BN support rods.

Study on the Emission Properties of the Impregnated Cathode With Nanoparticle Films

The effect of thin-film characteristics on the thermionic emission of dispenser cathodes has been investigated. Nanoparticle Ir thin films were grown by magnetron sputtering at room temperature. Microstructures of these thin films grown at different sputtering pressures were observed using a scanning electron microscope. The results showed that the particle size of the films depended on the deposition rate in the nucleation stage of the Ir films, which could be well controlled by the sputtering pressure. N-type cathodes were fabricated by impregnating tungsten matrices of 25% porosity with 6:1:2-type barium calcium aluminate and then coating them with nanoparticle Ir thin films, 200-500 nm in thickness, in hydrogen at 1200°C. A comparison was made in the emission uniformity between an N-type cathode (defined here as a Ba dispenser cathode coated with a layer of metal nanoparticles) and a traditional M-type cathode using a thermionic electron microscope. The chemical components of the vacuum background, the evaporants from an N-type cathode, and an M-type cathode were respectively analyzed using a time-of-flight mass spectrometer. The evaporating rates of the two types of cathodes and their dependence on the cathode temperatures were also investigated. Finally, the electron emission performance of the N-type cathodes was studied.

Development of an S-band 22-kW-Average-Power-Klystron With 7.14% Relative Bandwidth

This paper presents the design considerations, simulation results, and test results for an S-band 22-kW-average-power 7.14%-relative-bandwidth klystron design with 4-min startup, which was developed in the Institute of Electronics, Chinese Academy of Sciences (IECAS) before December 2009. Ten klystrons were built and tested. Over 1.1-MW peak output power with 7.14% relative bandwidth was measured at a 2% radio-frequency (RF) duty cycle. The measured startup time is 4 min. A method of supplying the heater with electricity is proposed, the manner of improving the RF output performance is also described, and both of them have been validated through the further experiments with a specialized electron gun and the hot-test results of the klystron, respectively.

Reliability Analysis of Thermal Conduction of Slow-Wave Structures Assembled With Different Methods

This paper presents the study on the thermal conduction reliability of the helix traveling-wave-tube (TWT) slow-wave structure (SWS), considering two affecting factors, such as the outside thermal condition and the manufacturing process. ANSYS has been used to analyze the variation of the heat dissipation capability of the SWS under different thermal conditions. Several experimental tests have been implemented to study the effect of the manufacturing process on the thermal conduction of the SWS. The conclusions obtained are expected be a valuable aid to the manufacture of helix TWT.

Improvement of Heat Dissipation Capability of Slow-Wave Structure Using Two Assembling Methods

Two assembling methods, i.e., the sputter brazing method and the diffusion brazing method, have been developed for improving the heat dissipation capability of the helix traveling-wave tube slow-wave structure (SWS). The magnetron sputter plating technology and the pressure diffusion technology are employed in this letter to complete the SWS assembly. The effect of these two methods on the thermal conduction of the SWS was verified by several experimental tests. These two methods being pursued enable better heat dissipation capability of the helix SWS, compared to the conventional nonbrazing methods.

Improvement of the Performance of a Helix Slow-Wave Structure With a Copper-Embedded Barrel

The effect of a copper-embedded barrel on the performance of a helix slow-wave structure (SWS) has been studied theoretically and experimentally. The heat dissipation capability and cold-test characteristics of the SWSs with a monel barrel, a normal copper barrel, and a copper-embedded monel barrel have been analyzed and compared. With its combination of high mechanical strength and good thermal conductivity, the copper-embedded monel barrel enables better heat dissipation capability than the other barrel types and has low RF losses.

Analysis of thermal interface resistivity of a helix TWT slow-wave structure

The thermal interface resistivity (TIR) of the helix slow-wave structure (SWS) is studied theoretically and experimentally. The effects of the TIRs at different interfaces on heat dissipation capability of the SWS have been analyzed and compared using ANSYS. The TIRs at the helix-rod interface and the rod-barrel interface have been calculated respectively with the developed equations and the measured component temperatures, considering the temperature- -dependent material properties. The effects of the rod material and the assembly method on the TIRs of the SWS were analyzed and compared.

Effect of Plated Metal Film on the Performance of Helix TWT Slow-Wave Structure

The effect of the plated metal film on the heat dissipation capability and cold-test characteristics of the helix slow-wave structure (SWS) have been studied in several experimental tests and computer simulations. The thermal conduction and the power losses of the helix SWS were improved by using a plated helix. A brazed SWS with end-plated rods exhibits excellent heat dissipation capability. The side-plated rods affect the cold-test characteristics of the SWS.

Improvement of Heat Dissipation Capability of Vacuum Device Using Iridium Nanoparticulate Film

The effect of the iridium nanoparticulate film on heat dissipation capability of the vacuum device has been studied in this letter. In the experimental tests, the copper barrels of the slow-wave structures have been deposited with normal-Ir film and nano-Ir film, respectively. The radiation emissivity coefficients of differential materials have been accurately calculated using the experimental results, and then applied in the computer simulation. The agreement between the experimental results and the simulation results is excellent, suggesting that the iridium nanoparticulate film enables much better heat radiation performance than the normal metal materials.