Christopher James Lingwood

Automatic Optimization of a Klystron Interaction Structure

The design of klystrons has long been a manual process guided by experience. However, with well-defined specifications and sufficiently rapid simulation methods, it is a good candidate process for automatic optimization techniques. In this paper, such a technique is evaluated and refined using klystron specific techniques, leading to several designs (with different tradeoffs between efficiency and size) each of a structure comparable with the SLAC B-factory klystrons. The most efficient of which, while only 1% more efficient, is 17.1% shorter.

Phase space analysis of multipactor saturation in rectangular waveguide

In certain high power RF systems multipactor cannot be avoided for all operating points, but its existence places limits on performance, efficiency, lifetime, and reliability. As an example multipactor in the input couplers of superconducting RF cavities can be a major limitation to the maximum RF power. Several studies have concentrated on rectangular waveguide input couplers which are used in many light sources. Most of these studies neglect space charge assuming that the effect of space charge is simply to defocus the electron bunches. Modelling multipactor to saturation is of interest in determining the performance of waveguide under a range of conditions. Particle-in-cell modelling including space charge has been performed for 500 MHz half-height rectangular waveguide. Phase plots of electron trajectories can aid understanding the processes taking place in the multipactor. Results strongly suggest that the multipacting trajectories are strongly perturbed by space charge causing the electrons to transition from two-surface to single-surface trajectories as the multipactor approaches saturation.

High efficiency multiple beam klystron (MBK) cavity properties

For the design of a high efficiency MBK the calculation of the properties of resonant cavities is critical. A method of moments can be used to find these properties quickly and to a known accuracy.

A Millimeter-Wave Klystron Upconverter With a Higher Order Mode Output Cavity

Manufacturing of klystrons in the millimeter-wave frequency range is challenging due to the small size of the cavities and the ratio of the maximum gap voltage to the beam energy. The small dimensions also make difficult to produce devices with the output power required by a number of applications at millimeter wave, such as communications and spectroscopy. Operating with a higher order mode can be a potential solution, as a larger transverse size structure can be used. Unfortunately, high-order mode cavities have a lower impedance than in fundamental mode. In this paper is proposed a novel solution to overcome the reduced impedance by utilizing an upconverter, where all cavities except the output cavity are designed to work in high-order mode. To demonstrate the effectiveness of the approach, two klystron upconverters were designed. One has six cavities aiming to achieve a maximum output power of ~90 W at 105 GHz. The second klystron upconverter was a simpler three-cavity structure designed for quick prototype. Millimeter-wave measurements of the three-cavity klystron upconverter are presented.

2-D particle-in-cell simulations of high efficiency klystrons

Currently, klystrons employing monotonic bunching offer efficiencies on the order of 70%. Through the use of the core oscillation electron bunching mechanism, numerical simulations have predicted klystrons with efficiencies up to 90%. In this paper, we present PIC simulations of such geometries operating at a frequency of 800 MHz, with efficiencies up to 83% predicted thus far.

Rapid calculation of the properties of klystron cavities

This paper shows how the properties of cylindrically symmetrical klystron cavities can be computed quickly and accurately using the method of moments. The method can be used to benchmark results obtained using computer codes based on the discretisation of the volume of the cavity.

submitter : Particle-in-cell simulation of second and third harmonic cavity klystron

This paper outlines the results obtained from Magic software for the CSM_23 (Core Stabilization Method) klystron. This klystron implements the use of a second and third harmonic klystron to increase the efficiency. From the PIC simulation an efficiency of 78.1% was achieved.

MAGIC2-D simulations of high efficiency klystrons using the core oscillation method

Klystrons employing traditional monotonic electron bunching are capable of efficiencies up to ∼70%. The use of the core oscillation method (COM) of electron bunching has predicted a significant improvement in efficiency towards 90%. Here, we document refinements on previously presented geometries, with PIC simulations predicting efficiencies up to 85%.

Particle-in-cell simulation of the third harmonic cavity F-Tube klystron

Use of a second harmonic and third harmonic cavity within a klystron to increase efficiency has been studied using particle-in-cell (PIC) code, MAGIC 2D. The six cavity device has a drive frequency of 1GHz, a predicted efficiency of 88%, 39 dB gain and an output power of 833 kW. The preliminary simulation results have revealed indications of bunching with bunch core oscillations. The initial results and analysis of the F-Tube PIC study are presented.

Saturation of multipactor in rectangular waveguide

Summary form only given. Multipactor is a limiting factor in a many RF systems, restricting performance, efficiency, lifetime and reliability. In many situations it is possible to avoid multipactor by various suppression methods or the avoidance of specific operating points. However this cannot always be achieved. When multipactor cannot be avoided, the saturation level becomes critical. In for instance, superconducting applications, multipactor which does not saturate at a low level can limit peak power.