The development ofhigh power klystrons requires computer codes simulating the complex interaction of electrons with the electromagnetic field as realistically as possible. We present a three dimensional computer simulation of a klystron output circuit including fully relativistic particle dynamics. The power extraction is simulated with the realistic waveguide geometry bounded by a broadband waveguide boundary condition. The data base for the injection of the beam in the output circuit is derived from the steady state solution of a two dimensional simulation of the first klystron cavities. The interface between rotationally symmetric and nonsymmetric part includes not only the particle parameters but also the electromagnetic field at the interface plane.. Results are presented for a 150 MW S-band klystron, which was designed and built at the Stanford Linear Accelerator Center (SLAC) as a part of an international collaboration with Deutsches Elektronen Synchrotron (DESY). The simulations were performed by using the electromagnetic simulator MAFIA.

Three Dimensional Klystron Simulation

To facilitate the design of high power klystrons an investigation into the reliability and accuracy of three modern particle-in-cell codes was performed. A 150 MW S-band klystron for which measurements were available was used for this comparison. The field calculations of the particle-in-cell codes are based on a finite difference time domain scheme, and use a port approximation to speed up the convergence to steady state. However they differ in many details (e.g. calculation of E, B or A, /spl phi/; space charge correction; 2D or 3D modelling of the output cavity).

/pdf/comparison-of-condor-fci-and-mafia-calculations-for-a-150-mw-3eezwjsp2m.pdf

Comparison of CONDOR, FCI and MAFIA calculations for a 150 MW S-band klystron with measurements

High Power Microwave (HPM) system efficiency has typically been calculated by dividing the peak output power by the peak input power or the input power at the time of the peak output power. This method is typically chosen over energy based calculations because of the difficulties in obtaining an accurate power envelope for certain HPM sources. Power based efficiency calculations have also traditionally excluded any sub-systems which can be highly inefficient. As HPM systems begin moving from lab to field operation the power based efficiencies calculations fall well short of accurately characterizing the complete system. Efficiency calculations should instead be based on energy, typically in the form of fuel or batteries, as they are the major limiting components of any mobile system.

Energy efficiency of High Power Microwave systems

Spurious oscillations in high power klystrons are found to occur in the gun region, in the cavities in the main body of the tube, or in the drift tunnel. The criteria that determine whether a mode will oscillate is that its beam loading be negative, and that the power it extracts from the beam exceeds its losses to external loading and wall dissipation. Using the electromagnetic and particle-in-cell modules of MAFIA, we have devised numerical techniques with which the quality factors Q/sub b/, Q/sub e/, and Q/sub o/ can be evaluated and compared. Simulations involving a gun oscillation observed in the SLAC/DESY S-band klystron will be reported.

/pdf/spurious-oscillations-in-high-power-klystrons-9sp5tvik7i.pdf

Spurious oscillations in high power klystrons

A super-power, high voltage klystron (10) includes an output cavity (18) operating in the TM01X mode, where X is greater than zero.

Tm01x mode (x 0) klystron resonant cavity

As part of an international collaboration, the Stanford Linear Accelerator Center (SLAC) klystron group has designed, fabricated and tested a 60 Hz, 3 /spl mu/s, 150 MW klystron built for Deutsches Elektronen Synchrotron (DESY). A test diode with a 535 kV, 700 A electron beam was constructed to verify the gun operation. The first klystron was built and successfully met design specifications. This paper discusses design issues and experimental results of the diode and klystron including the suppression of gun oscillations. >

/pdf/the-design-and-performance-of-150-mw-s-band-klystrons-1uzqw31d29.pdf

The design and performance of 150-MW S-band klystrons

http://inspirehep.net/record/378427/files/slac-pub-6677.pdf

D. Sprehn

Papers

The design and performance of 150-MW S-band klystrons

The Design and performance of 150-MW S band klystrons