A novel slotted helix slow-wave structure for high power Ka-band traveling-wave tubes

A novel slotted helix slow-wave structure （SWS） is proposed to develop a high power, wide-bandwidth, and high reliability millimeter-wave traveling-wave tube （TWT）. This novel structure, which has higher heat capacity than a conven- tional helix SWS, evolves from conventional helix SWS with three parallel rows of rectangular slots made in the outside of the helix tape. In this paper, the electromagnetic characteristics and the beam-wave interaction of this novel structure operating in the Ka-band are investigated. From our calculations, when the designed beam voltage and beam current are set to be 18.45 kV and 0.2 A, respectively, this novel circuit can produce over 700-W average output power in a frequency range from 27.5 GHz to 32.5 GHz, and the corresponding conversion efficiency values vary from 19% to 21.3%, and the maximum output power is 787 W at 30 GHz.

Durability experiment on anti-electron-bombardment of RE_2O_3-Mo secondary emission material

A durability test to determine anti-bombardment sensitivity of multi-RE2O3-Mo secondary emission material was carried out and the variation of maximum secondary emission coefficient （δ）max)) was monitored at regular intervals. After the experiment, the cathode was analyzed with SEM, EDS and XRD techniques. The results show that δ)max) of multi-RE2O3-Mo cermets cathode heated to 1 100 ℃ under electron bombardment of 300 W/cm2 reaches the peak of 3.35 at 200 h. After 500 h of bombardment, the maximum secondary-electron-yield curve stabilizes. The δ)max) value of the cathode remains at about 2.5 after 1 000 h and represents a good anti-bombardment property. The high δ)max) value of the cathode is related with formation of an enriched Y2O3 layer on the surface under high temperature and with the amount of La2O3 particles in the shape of nanometer distributed on the surface. Under the experimental conditions, the drop of δ)max) value may be caused by the reduction of La2O3 content and the porous layer resulted from evaporation of MoO2, which is formed when Mo at the surface is oxidized.

Experiment of Microwave Heating on Self-Fluxing Pellet Containing Coal

Based on the phase diagrams and the mass action law in combination with the coexistence theory of metallic melts structure, the calculation model of mass action concentration for Mg-Al, Sr-Al and Ba-Al was built, and their thermodynamic parameters were determined. The agreement between calculated and measured results shows that the model and the determined thermodynamic parameters can reflect the structural characteristics of relevant melts. However, the fact that the thermodynamic parameters from literature don ′t give the value agree with the measured result may be due to unconformity of these parameters to real chemical reactions in metallic melts.

Two-Dimensional Simulation of Hydrogen Direct-Current Discharge Plasma

A two-dimensional model of a weakly-ionized hydrogen direct-current （DC） discharge at low pressure is simulated. In the model, the metal electron overflow and secondary electron emission coefficient at the cathode spot axe introduced to represent the relationship between the electron and ion density, and the electron energy distribution function is expressed by kinetic theory. The electron current density and reaction constant reasonably set on the boundary are discussed. It is determined that 11 collision reactions play a major role in low pressure and weakly ionized hydrogen discharge. On this basis, the relationship between mobility, electrode spacing, and breakdown voltage is verified. Good agreement is achieved between the simulation curve and Paschen curve.

Aluminum Nitride for High Brightness LED Packaging Applications

Aluminum Nitride(ALN)is a high thermal conductivity material which is being used with increasing frequency in packaging applications for high brightness LEDs(HBLED).This paper introduce Aluminum Nitride substrate fabrication process and different ALN metallization approaches.It is clear that the most technically appropriate metallization approach for HBLED packging is DPC.This paper explain why the cost of ALN substrate is so high and give the future of ALN in HBLED applications.

The nonresonant perturbation theory based field measurement and tuning of a linac accelerating structure

Assisted by the bead pull technique,nonresonant perturbation theory is applied for measuring and tuning the field of the linac accelerating structure.The method is capable of making non-touching amplitude and phase measurements,real time mismatch feedback and field tuning.Some key considerations of the measurement system and of a C-band traveling-wave structure are discussed,and the bead pull measurement and the tuning of the C-band traveling-wave linac accelerating structure are presented at last.

RF gun for an intense THz radiation source

A new facility is under construction at the Shanghai Institute of Applied Physics, to generate femto-second electron bunches and intense coherent THz radiation pulses. A thermionic RF-gun is used to be the electron source of the linac, which is 1.6 cell, π/2, side coupled in design. In the following of this paper, the design, manufacture and beam operation of this gun are presented.