Designers of high power amplifiers generally regard the region above 300 MHz as a domain dominated by velocity modulated (klystron/TWT) devices. However, as the power requirements diminish, there are attractive alternatives. The high power 850 MHz requirements of the ground test accelerator (GTA) program can be filled by 1 MW klystrons, but it would be more efficient to use a lower power device for a 50 kW requirement. To meet the 850 MHz medium power requirements, Los Alamos National Laboratory is developing an 850 MHz tetrode amplifier. These amplifiers will provide RF power to the momentum compactor and bunch rotator cavities of the GTA. Available tubes provide only a limited safety margin for a low risk design at the power levels and duty factor required for GTA cavities. At 850 MHz, the output power capability of available tubes is reduced because of transit time effects and limited anode voltage holdoff. Pulsing the anode of the output tetrode amplifier will allow higher output power with minimum design risk. A floating deck modulator acts as a high voltage/high current switch, so voltage is applied to the anode of the gridded tube only during the RF pulse. The anode voltage holdoff capability of the tube is substantially enhanced by operating in this mode. The design of the floating deck modulator and its impact on the design risk of the 850 MHz tetrode amplifier is described.
Presented at the 1990 LINAC Conference
- Pub Date:
- Microwave Amplifiers;
- Linear Accelerators;
- Traveling Wave Tubes;
- Electronics and Electrical Engineering