Yan-Wen Liu

Preparation and Evaluation of the Ammonium Perrhenate Impregnated Ni Sponge Oxide Cathode

To improve emission performance of the Ni sponge oxide cathodes, a Ni-Re sponge was prepared by impregnating an Ni sponge in an ammonium perrhenate (NH4ReO4) solution and then a cathode was fabricated using this Ni-Re sponge. At 850°Cbr, the dc emission current density of a typical impregnated Ni-Re sponge cathode is 5.21 A/cm2 and the pulsed emission current density reaches 35.6 A/cm2 with a 10- μs pulsewidth. Lifetime tests were carried out under different temperatures. After working under 800°C for 3000 h, the decreases of the dc emission current density is less than 5% from the initial value of 1.63 A/cm2. Under 780°C, the dc emission current density even rises instead of attenuating and is still 14% higher than the initial value of 1.0 A/cm2 after 5000 h of operation. Furthermore, the thermal electron spectrometry analysis and the work function distribution test show that the emission uniformity of the Ni-Re sponge oxide cathode fabricated by this liquid-solid mixing method is better than that of the conventional Ni-Re sponge oxide cathode fabricated by the solid-solid mixing method.

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.

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.

Preparation and performance of the ammonium perrhenate impregnated W matrix Ba-W cathode

In this paper we mainly describes the research progress in a kind of ammonium perrhenate impregnated W matrix Ba-W cathode, which includes the preparation of W-Re matrix by impregnated ammonium perrhenate solution and the cathode properties testing. The lifetime testing results show that the emission current, after 16056h lifetime at a temperature of 1000 °Cbr, has still increased more than 8% with 3.0 A/cm2 DC current.

Emission uniformity of the ammonium perrhenate impregnated Ni sponge oxide cathode

In order to improve emission performance of the Ni sponge oxide cathodes, an ammonium perrhenate impregnated Ni Sponge Oxide Cathode has been developed by IECAS. In this paper we mainly describe the research on the emission uniformity of this cathode with the thermal electron spectrometry analysis and the work function distribution test. The test results indicates that the emission uniformity of the Ni-Re sponge oxide cathode fabricated by this liquid-solid mixing method is better than that of the conventional Ni-Re sponge oxide cathode fabricated by the solid-solid mixing method.

Influence of new material and technology on oxide cathode performance

The oxide cathode is one of the most commonly used electron sources in vacuum tubes. Continual improvement of vacuum tubes requires better and better current emission performance of their electron sources. In this context, new type oxide cathodes have been emerging incessantly in the past century, such as Ni sponge oxide cathode, rare oxide cathode and reservoir oxide cathode. Nonetheless, there is still room for further improvement. In this paper we mainly describe the research process on Ni-Sc sponge oxide cathode, ammonium perrhenate impregnated Ni sponge oxide cathode and plasma spraying oxide cathode. Moreover, we also developed the quick warm-up cathode depend on oxide cathode low operation temperature and simple structure.

Life Test Studies on Dispenser Cathode With Dual-Layer Porous Tungsten

This paper introduces a newly developed dual-layer porous tungsten dispenser cathode, which can meet the growing requirements on both life and current density. In comparison with the conventional dispenser cathodes, the new-type dispenser cathodes have higher emission current density, lower evaporation rate and longer lifetime. According to the results of the life tests and the related analysis, their longest lifetime at a 1.5 A/cm2 current density under 974 °Cbr is estimated to be over 1.9 ×105 h.

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.

A new method for study of the evaporation rate of cathodes

A new method has been introduced to study the evaporation of barium from cathodes by using time-of-flight mass spectrometer (TOFMS). The formula of evaporation rate will be given in this paper.