High-Power High-Efficiency L-band Multiple-Beam Klystron Development at CPI
Communications and Power Industries, Inc., has designed and manufactured two versions of a 10-MW-peak high-efficiency multiple-beam klystron (MBK) operating at 1300 MHz. This type of klystron is favored for large particle accelerator projects such as the European X-ray Free-Electron Laser at the Deutsches Elektronen Synchrotron (DESY). Two klystrons have been made for DESY. The first-generation MBK was a vertically oriented prototype using a six-cavity design with higher order mode input and output cavities and conventional intermediate cavities. For cost and performance reasons, the second-generation MBK, designated VKL-8301B, utilized seven coaxial fundamental-mode cavities and is an “industrialized” horizontally oriented klystron. The klystron was designed and optimized using state-of-the-art multidimensional design codes to ensure that all performance requirements are exceeded. Agreement between the simulated and measured performances is good. The VKL-8301B prototype achieved a peak saturated RF output power of 10.4 MW and 67.8% efficiency. The data were measured at the full 1.5% duty and with 1.5-ms pulse width. The klystron satisfied all required operating conditions, including stable operation into an output mismatch of 1.2:1 voltage standing wave ratio at various phases. The prototype has been shipped to DESY and has been successfully tested by a customer.
3-D Simulations and Design of Multistage Depressed Collectors for Sheet Beam Millimeter Wave Vacuum Electron Devices
There is an increasing interest in sheet electron beam-based vacuum electron devices from the microwave through terahertz region. As with standard pencil beam devices, it is desirable to increase overall net efficiency through the use of multistage depressed collectors. The sheet electron beam, however, brings unique challenges to this task due to the elliptical cross section of the beam. This paper focuses on the comprehensive 3-D simulation modeling of the electron beam dynamics for the ac modulated sheet beam topology from the beam-wave interaction region up to the designed energy recovery structure, i.e., the multistage depressed collector. For purposes of illustration, the design and analysis of a five-stage depressed collector for a W-band sheet beam klystron using the 3-D electromagnetic particle-in-cell (PIC) finite difference time domain code MAGIC is described herein. Numerous PIC simulations were carried out to determine the optimum operating parameters. The effects of the secondary electrons on the recovery efficiency and the electron back streaming were both investigated. To accommodate the elliptical cross section of the sheet beam, the option of adding a racetrack-like structure to decrease the back streaming was also explored. Through optimization, a recovery efficiency of 88.38% was achieved, with a minimized total electron back-streaming fraction of 0.25%.
Cognitive Correlaretes of Physics Achievement of Some Nigeria Senior Secondary Students
Some cognitive correlates of physics achievement of some Nigeria senior secondary students were considered in the study. Specifically, the study examined the relationship between measures of student’s field independency. Cognitive tasks, formal reasoning and their achievement in physics. Purposive and stratified random sampling techniques were employed to obtain a sample of 524 senior secondary two students from six education zones in Kogi State of Nigeria. Three instruments were used. They are science Reasoning Tasks (SRTs). Group Embedded Figures Test (GEFT) and Physics Achievement Test (PAT). Data analysis using multiple regressions reveals that measures of students’ fields’ independency and cognitive tasks predicted student’s achievement in physics generally. However, only measure of field independency predicted students’ achievement in physics in the higher order cognitive demand questions. Measures of formal reasoning had no significant relationship with students’ achievements in physics generally or in higher order cognitive demand questions in physics. However, the overall relationships between measures of field independency, cognitive tasks, formal reasoning and students’ achievement in physics generally and in higher order cognitive demand questions in physics were both significant. Educational implications of these findings were discussed.