Solid State Power Amplifier for 805 MegaHertz at the Los Alamos Neutron Science Center

Particle accelerators for protons, electrons, and other ion species often use high-power vacuum tubes for RF amplification, due to the high RF power requirements to accelerate these particles with high beam currents. The final power amplifier stages driving large accelerators are unable to be converted to solid-state devices with the present technology. In some instances, radiation levels preclude the use of transistors near beamlines. Work is being done worldwide to replace the RF power stages under about ten kilowatts CW with transistor amplifiers, due to the lower maintenance costs and obsolescence of power tubes in these ranges. This is especially practical where the stages drive fifty Ohm impedance and are not located in high radiation zones. The authors are doing this at the Los Alamos Neutron Science Center (LANSCE) proton linear accelerator (linac) in New Mexico. They replaced a physically-large air-cooled UHF power amplifier using a tetrode electron tube with a compact water-cooled unit based on modular amplifier pallets developed at LANSCE. Each module uses eight push-pull bipolar power transistor pairs operated in class AB. Four pallets can easily provide up to 2,800 watts of continuous RF at 805 MHz. A radial splitter and combiner parallels the modules. This amplifier has proven to be completely reliable after over 10,000 hours of operation without failure. A second unit was constructed and installed for redundancy, and the old tetrode system was removed in 1998. The compact packaging for cooling, DC power, impedance matching, RF interconnection, and power combining met the electrical and mechanical requirements. CRT display of individual collector currents and RF levels is made possible with built-in samplers and a VXI data acquisition unit

A Review of Strategic Process Research

This article reviews research on the process of strategic management reported over the last six years in seven leading journals. Nine "streams" of work are identified and critiqued. The field is described as giving continuing attention to the possibilities and problems of strategic planning and decision making, but also moving into new areas of research - especially the problem of how the attention of decision makers is directed toward specific agendas for action. We recommend more studies that simultaneously consider strategy formulation and implementation and more studies that attempt to integrate methods and concerns across the various areas of process research. Finally, we recommend that future research give simultaneous attention to the content as well as the process of strategy