Numerical Optimization of a Multistage Depressed Collector With Secondary Electron Emission for an X-band Gyro-BWO

A three-stage depressed collector was previously designed and simulated to recover the kinetic energy of the spent electron beam in an X-band gyrotron backward wave oscillator (gyro-BWO) by using the 3-D particle-in-cell code MAGIC. The geometry of the depressed collector was optimized using a genetic algorithm to achieve the optimum overall recovery efficiency for specific parameters of the spent beam. In this paper, secondary electron emissions were simulated, and a few emission models were compared to investigate the effects of the secondary electrons on the overall recovery efficiency and the backstreaming of the electrons from the collector region. The optimization of the shape and dimensions of each stage of the collector using a genetic algorithm achieved an overall recovery efficiency of more than 80% over the entire operating regime of the Gyro-BWO, with a minimized backstreaming of 1.4%. The heat distribution on the collector was calculated, and the maximum heat density on the electrodes was approximately 195 W/cm2, hence avoiding the generation of ¿hot spots¿.

[1]  C. Case,et al.  MOLIERE'S THEORY OF MULTIPLE SCATTERING. , 1968 .

[2]  J. L. Saunderson,et al.  Multiple Scattering of Electrons , 1940 .

[4]  Furman,et al.  Simulation of secondary electron emission based on a phenomenological probabilistic model , 2003 .

[5]  F. Sterzer.  Improvement of traveling-wave tube efficiency through collector potential depression , 1958, IRE Transactions on Electron Devices.

[6]  M. Furman,et al.  Probabilistic Model for the Simulation of Secondary Electron Emission , 2002 .

[7]  R. Lye,et al.  Theory of Secondary Emission , 1957 .

[8]  V. Granatstein,et al.  Corrections to "Advancements in codes for computer aided design of depressed collectors and tracing , 2002 .

[9]  H. Hunger,et al.  Measurements of the Electron Backscattering Coefficient for Quantitative EPMA in the Energy Range of 4 to 40 keV , 1979, November 16.

[10]  R. M. Vaughan,et al.  Secondary emission formulas , 1993 .

[11]  Stephen M. Seltzer,et al.  Electron-photon Monte Carlo calculations: The ETRAN code , 1991 .

[12]  J. Burns.  ANGULAR DISTRIBUTION OF SECONDARY ELECTRONS FROM (100) FACES OF COPPER AND NICKEL , 1960 .

[13]  K. Ronald,et al.  Gyro-BWO experiments using a helical interaction waveguide , 2005, IEEE Transactions on Electron Devices.

[14]  Rainee N. Simons,et al.  Advances in Space Traveling-Wave Tubes for NASA Missions , 2007, Proceedings of the IEEE.

[15]  G. D. Valdez,et al.  ITS: the integrated TIGER series of electron/photon transport codes-Version 3.0 , 1991, Conference Record of the 1991 IEEE Nuclear Science Symposium and Medical Imaging Conference.

[16]  Gregory S. Nusinovich,et al.  Theory of gyro-backward wave oscillators with tapered magnetic field and waveguide cross section , 1996 .

[17]  A. D. R. Phelps,et al.  Design of an energy recovery system for a Gyrotron backward wave oscillator , 2008, 2008 17th International Conference on High Power Particle Beams (BEAMS).

[18]  V. Granatstein,et al.  Design of a multistage depressed collector system for 1 MW CW gyrotrons. II. System consideration , 1999 .

[19]  P. R. Barker,et al.  Secondary electron emission in the scanning electron microscope , 1978 .

[20]  Richard True,et al.  The MICHELLE three-dimensional electron gun and collector modeling tool: theory and design , 2002 .

[21]  J. Vaughan,et al.  A new formula for secondary emission yield , 1989 .

[22]  Manfred Thumm,et al.  A new approach for a multistage depressed collector for gyrotrons , 2000 .

[23]  Sergey V. Samsonov,et al.  Theory and simulations of a gyrotron backward wave oscillator using a helical interaction waveguide , 2006 .

[24]  Victor L. Granatstein,et al.  Design of a multistage depressed collector system for 1-MW CW gyrotrons. I. Trajectory control of primary and secondary electrons in a two-stage depressed collector , 1999 .

[25]  L. Reimer.  Scanning Electron Microscopy: Physics of Image Formation and Microanalysis , 1984 .