Large signal klystron simulations using a curnow circuit model

Summary form only given. Simulation codes used for large signal analysis of coupled cavity traveling wave tubes commonly use a lumped element model of the traveling wave circuit due to Curnow. When the circuit unit cells are not connected to one another, we show that for suitable choices of lumped element circuit parameters, a Curnow cell can be used to model klystron input, buncher, or output cavities, thereby enabling a coupled-cavity simulation code based on the Curnow circuit to be used to simulate klystrons. In the absence of loss, the Curnow cell is defined by the specification of 6 lumped element values, basically 4 inductances and 2 capacitances. The addition of loss adds a seventh value, for a resistor. To model a klystron input cavity, for example, a designed might specify the resonant frequency of the cavity, R/Q, Q_internal, and Q_external. In addition, we assume that the impedance of the transmission line from the driver to the input cavity is specified. We show that specification of these physical quantities permits specification of all of the lumped element values of the Curnow circuit. An approximate analysis, assuming large values of Q and frequencies near the cold cavity resonant frequency, has produced analytic forms for the Curnow parameters in terms of the physical parameters characterizing the klystron cavities. The klystron model is being implemented in the coupled-cavity version of the CHRISTINE code, which will be used to study klystron designs for frequency multiplication (harmonic generation) at very high drive levels. The analysis leading to the extraction of the Curnow parameters from the physical parameters that specify the klystron cavities, and sample results from the CHRISTINE code will be discussed