Development of Flat-Topped RF Voltage for TRIUMF

A Test Facility with operating characteristics equivalent to the TRIUMF RF system was used to generate a flat-topped RF dee voltage at full operating values. The fundamental at 23 MHz, and the third harmonic at 69 MHz were combined in the single resonator. No difficulty was encountered with multipactoring in the addition of the third harmonic when the fundamental voltage was on at the level of a few kilovolts. Since the TRIUMF dees are flattened coaxial λ/4 lines with uniform dee-to-liner spacing, the natural frequencies f
₁
and f
₃
fall quite near a 3/1 ratio. Only a slight warping of the resonator in two locations that affect f
₁
and f
₃
differently is required to tune for a given f
₁
and for f
₃
= 3f
₁
, precisely. With the two high power signals (1800 kW at 23 MHz and ~-100 kW at 69 MHz in TRIUMF; 45 kW and ~4 kW in the Test Facility) combined in one resonator, rather large filters in addition to the impedance matching networks are required in each drive line for isolation of the transmitters. The results of the tests and the physical layout will be described as well as the control systems for autotuning and for amplitude and phase of the two voltages.