A Unique High Duty Factor Series Hard-Tube Moduiator for Use in the Los Alamos Meson Physics Facility

The design criteria for the Los Alamos Meson Physics Facility (LAMPF) specifies an initial capability for 6% duty factor (DF), 16.7-mA peak beam current (1-mA average) with provisions for eventual operation at a 12% DF, 8.3-mA peak beam current (also 1-mA average). The first four accelerator cavities in LAMPF will be of the Alvarez type operating at 201.25 MHz and each having a Q of approximately 50,000. This combination of frequency and Q, together with the overdrive provisions built into the rf systems dictate a cavity fill time of 200 ??sec. If this 200 psec is added to the ultimate design of 12% DF beam, (1000 psec pulse, 120 Hz), it is found that a 14.4% DF rf system (1200 psec pulse, 120 Hz) is necessary to satisfy the ultimatd design limits of IAMPF. The last three of the four Alvarez cavities require approximately 3-MW peak rf power each at the afore-mentioned 14.4% ultimate DF. This power must be controlled over a dynamic range of approximately 30% during the usable part of the pulse while maintaining a cavity field amplitude tolerance of ?? 1.5%. The system must also be capable of overdriving the Alvarez cavity approximately 30% during turn-on to enhance the cavity field pulse rise time. This then dictates an overall control range of about 50%, i. e., (2-4 Mw) for the rf modulator system. The 201.25-MHz rf systems in LAMPF will use a series hard-tube modulator for control of rf power.