Design and development of radio frequency output window for circular electron–positron collider klystron

This paper presents the first phase of design, analysis, and simulation for the klystron coaxial radio frequency（RF）output window. This study is motivated by 800 kW continuous wave（CW）, 650 MHz klystrons for the future plan of circular electron–positron collider（CEPC） project. The RF window which is used in the klystron output section has a function to separate the klystron from the inner vacuum side to the outside, and high RF power propagates through the window with small power dissipation. Therefore, the window is a key component for the high power klystron. However, it is vulnerable to the high thermal stress and multipacting, so this paper presents the window design and analysis for these problems. The microwave design has been performed by using the computer simulation technology（CST） microwave studio and the return loss of the window has been established to be less than-90 d B. The multipacting simulation of the window has been carried out using MultiPac and CST particles studio. Through the multipacting analysis, it is shown that with thin coating of TiN, the multipacting effect has been suppressed effectively on the ceramic surface. The thermal analysis is carried out using ANSYS code and the temperature of alumina ceramic is lower than 310 K with water cooling.The design result successfully meets the requirement of the CEPC 650 MHz klystron. The manufacturing and high power test plan are also described in this paper.

Stock profiling using time–frequency‑varying systematic risk measure

This study proposes a wavelets approach to estimating time–frequency-varying betas in the capital asset pricing model(CAPM)framework.The dynamic of systematic risk across time and frequency is analyzed to investigate stock risk-profile robustness.Furthermore,we emphasize the effect of an investor’s investment horizon on the robustness of portfolio characteristics.We use a daily panel of French stocks from 2012 to 2022.Results show that varying systematic risk varies in time and frequency,and that its short and long-run evolutions differ.We observe differences in short and long dynamics,indicating that a stock’s betas differently fluctuate to early announcements or signs of events.However,short-run and long-run betas exhibit similar dynamics during persistent shocks.Betas are more volatile during times of crisis,resulting in greater or lesser robustness of risk profiles.Significant differences exist in short-run and longrun risk profiles,implying a different asset allocation.We conclude that the standard CAPM assumes short-run investment.Then,investors should consider time–frequency CAPM to perform systematic risk analysis and portfolio allocation.

Surface roughness measurement and analysis of mechanical parts based on digital holography

We measure the surface roughness of the mechanical parts based on digital holography. A digital off- axis hologram recording setup for reflective samples is built. Firstly, the height reconstruction error 2.3% of the setup is calibrated by using the quartz step height standard （VLSI- SHS-880QC）. Then, the standard scribed-line model and the grinding roughness specimen are selected as the test samples and their surface roughness are 0.095 6 jam and 0.025 3 jam, with errors 6.3%, 0.9%, respectively. The results are in good agreement with the given roughness parameters. At last, we also analyze the window effect of the filter on the roughness measurement value based on digital holography. In conclu- sion, the paper demonstrated effectively that the digital holography could provide the surface feature for the rough- ness measurement with high accuracy.

Effect of optical illumination on DDR IMPATT diode at 36 GHz

A reverse biased p-n junction diode with proper resonant cavity and boundary conditions is able to generate rf power and shows normal DC and small signal properties designed with semiconductor materials like 4H-SiC, GaAs, InP, Si-based DDR IMPATT structure at Ka band with dark condition. But when it is exposed to optical illumination through a proper optical window for both top mounted（TM） and flip chip（FC） configuration,it shows the influence on the oscillator performances in that band of frequency. The simulated results are analyzed for 36 GHz window frequency in each of the diodes and relative differences are found in power output and frequency of all these diodes with variable intensities of illumination. Finally it is found that optical control has immense effect in both FC and TM mode regarding the reduction of output power and shifting of operating frequency from which optimization is done for the best optically sensitive material for IMPATT diode.