A pulse sequencer for the KAON factory beam chopper

The beam chopper consists of a low-loss transmission line center fed from a tetrode. The transmission line is terminated with a short-circuit at one end and an open-circuit deflector plate at the other end. The complex reflections from the open-circuited and short-circuited ends allow a single tetrode to generate a deflector pulse with good rise and fall times. The shape of the pulse at the deflector plate is extremely sensitive to the frequency of the grid driver pulse. A variation of 1 ns in timing significantly alters the deflector pulse. To provide the required pulse pattern, a FET based grid pulser and sequencer has been built. This sequencer is able to produce alternating narrow and wide 900 volt grid pulses with rise and fall times of 20 ns. Under computer supervision it is able to generate and control pulse patterns with a stability of ±125 ps. The pulse pattern is synchronized to an RF synthesizer to simulate operation with the 23 MHz TRIUMF cyclotron RF system