A NEW 201.25 MHZ HIGH POWER RF SYSTEM FOR THE LANSCE DTL

Long pulses of high proton current (greater than one millisecond at 17 mA) at LANSCE are limited by the duty factor (DF) of the 201.25 MHz RF system powering the 100 MeV DTL. The operating point of the existing triode final power amplifiers (FPA) is approximately 75% of the published maximum anode dissipation rating, but is at 90% of the allowable limit with a margin of safety for tuning excursions, voltage standing wave effects and electron tube manufacturing variations. A new RF power system is under development for increasing both peak power and DF. The FPA uses a Thales TH628 Diacrode  with pyrolytic-graphite grids. It doesn't require the large anode modulator of the present triode system. Lower mains power consumption and reduced water-cooling requirements are some advantages of this scheme. A TH781 tetrode is being tested as an intermediate stage, using a Thales cavity amplifier. When installed, the new system will reduce the total number of electron power tubes from twenty-four to seven for the LANSCE DTL. Aspects of the RF modeling, mechanical design, RF testing, and other system considerations will be presented.