PAC 2005 - List of Authors

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Ivanov, V.

Paper	Title	Page
WPAT080	Calculation of Beam-Loaded Q in High-Power Klystrons	4060
	J.F. DeFord, B. H. Held STAR, Inc., Mequon, Wisconsin V. Ivanov, K. Ko SLAC, Menlo Park, California
	Funding: Work supported by DOE SBIR Grant DE-FG02-03ER83776. Instabilities in the gun region of a high-power klystron can occur when there is positive feedback between a mode and an induced current on the quasi-steady state beam emitted by the gun cathode.* This instability is dependent on the gun voltage, is predicted on the basis of a negative beam-loaded Q. The established method for computing the beam-loaded Q of a cavity involves using a time-dependent electromagnetic particle-in-cell (PIC) code to track beam particles through the quasi-static gun fields perturbed by the electromagnetic fields of a cavity eigenmode.** The energy imparted to the beam by the mode is obtained by integrating the Lorentz force along the particle tracks, and this quantity is simply related to the beam-loaded Q. We have developed an alternative approach that yields comparable accuracy but is computationally much simpler. The new method is based on a much simpler time-independent electrostatic PIC calculation, resulting in much faster solutions without loss of accuracy. We will present the theory and implementation of the new method, as well as benchmarks and results from analysis of the XP-4 klystron that show a potential instability near 3 GHz. B. Krietenstein, et al., "Spurious oscillations in high-power klystrons," PAC95, 1995. *U. Becker, et al., "Simulation of oscillations in high-power klystrons," EPAC, 1996.

Paper

Title

Page

WPAT080

Calculation of Beam-Loaded Q in High-Power Klystrons

4060

J.F. DeFord, B. H. Held
STAR, Inc., Mequon, Wisconsin
V. Ivanov, K. Ko
SLAC, Menlo Park, California

Funding: Work supported by DOE SBIR Grant DE-FG02-03ER83776.

Instabilities in the gun region of a high-power klystron can occur when there is positive feedback between a mode and an induced current on the quasi-steady state beam emitted by the gun cathode.* This instability is dependent on the gun voltage, is predicted on the basis of a negative beam-loaded Q. The established method for computing the beam-loaded Q of a cavity involves using a time-dependent electromagnetic particle-in-cell (PIC) code to track beam particles through the quasi-static gun fields perturbed by the electromagnetic fields of a cavity eigenmode.** The energy imparted to the beam by the mode is obtained by integrating the Lorentz force along the particle tracks, and this quantity is simply related to the beam-loaded Q. We have developed an alternative approach that yields comparable accuracy but is computationally much simpler. The new method is based on a much simpler time-independent electrostatic PIC calculation, resulting in much faster solutions without loss of accuracy. We will present the theory and implementation of the new method, as well as benchmarks and results from analysis of the XP-4 klystron that show a potential instability near 3 GHz.

*B. Krietenstein, et al., "Spurious oscillations in high-power klystrons," PAC95, 1995. **U. Becker, et al., "Simulation of oscillations in high-power klystrons," EPAC, 1996.