The development of a new three-dimensional electron gun and collector design tool is reported. This new simulation code has been designed to address the shortcomings of current beam optics simulation and modeling tools used for vacuum electron devices, ion sources, and charged-particle transport. The design tool specifically targets problem classes including gridded-guns, sheet-beam guns, multibeam devices, and anisotropic collectors, with a focus on improved physics models. The code includes both structured and unstructured grid systems for meshing flexibility. A new method for accurate particle tracking through the mesh is discussed. In the area of particle emission, new models for thermionic beam representation are included that support primary emission and secondary emission. Also discussed are new methods for temperature-limited and space-charge-limited (Child's law) emission, including the Longo-Vaughn formulation. A new secondary emission model is presented that captures true secondaries and the full range rediffused electrons. A description of the MICHELLE code is presented.

The MICHELLE three-dimensional electron gun and collector modeling tool: theory and design

Summary form only given, as follows. The new conformal grid MICHELLE 3D Electron Gun and Collector modeling code has been used in a variety of design modeling efforts to test it s capabilities and show it s robustness. This MICHELLE code specifically addresses shortcomings of beam optics simulation and modeling tools, and targets problem classes including gridded-guns, sheet-beam guns, multi-beam devices, and anisotropic collectors. Additionally, features like improved emission models, including new thermionic, Child's law, and secondary emission models are discussed. As part of this effort, a new, comprehensive secondary emission model has been developed for MICHELLE in order to achieve an accurate beam collection design capability. The basic physics model in the code is based on the equilibrium steady state application of the electrostatic PIC approximation employing both hexahedral and tetrahedral grid systems. The code employs a multiblock architecture, allowing flexibility in gridding and memory use, as well as hardware architecture adaptability. The current version supports a multiblock, conformal, structured, hexahedral grid. The multiblock, unstructured, the tetrahedral version of the code is currently under development. The structure of the code is the following: The code employs a basic infrastructure that handles generic tasks like grid definition and memory management, down to basic utility functions including basic IO, post-processing IO, and vector algebra. New algorithms have been developed and are being implemented for calculation of particle trajectories on finite element grids. The code supports third-party CAD and Gridding tools allowing the user to make use of current in-house software. In addition, a Post Processor has being developed that is tuned for the tasks of modeling and analyzing output for gun and collector simulations. The code allows magnetic field profiles input from ANSOFT s Maxwell 2D/3D, and other similar software.

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The MICHELLE electron gun and collector modeling tool

The 3D finite-element gun and collector modeling code, MICHELLE, has been under development at SAIC in collaboration with industrial partners and national laboratories. This development program has been designed to address the shortcomings of current beam optics simulation and modeling tools for vacuum electron devices. The program specifically targets problem classes including gridded-guns, sheet-beam guns, multi-beam devices, and anisotropic collectors, with a focus on improved physics models. The code includes both structured and unstructured grid systems for meshing flexibility. Advances have been made in the areas of accurate particle tracking through the mesh and beam emission methods, including new models for thermionic, temperature-limited, Child's law and secondary emission.

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This thesis reports on the theory, design, and experimental investigation of a gyrotron travelling-wave-tube (TWT) amplifier at 140 GHz. The gyro-TWT uses the HE06 mode of a confocal geometry as its operating mode. The linear and nonlinear theory of the confocal waveguide is presented, along with a quasi-optical approach for describing the modes of a confocal waveguide. Both the equations of motion and the mode excitation equation are derived in detail. A beamlet code is introduced as a tool for calculating the linear and nonlinear gain of the azimuthally asymmetric confocal modes that interact with the electron beam with an annular distribution of electron guiding centers. This code has been successfully benchmarked against the code MAGY for azimuthally symmetric cases, and extends the capabilities of nonlinear gyroamplifier theory to configurations that lack azimuthal symmetry. The gyro-TWT experimental setup is presented in detail. Quasi-optical mode converters were designed, fabricated, and tested, ultimately achieving a coupling of -3 dB into the HE06 mode. The source of competing, parasitic oscillations was identified and addressed by the addition of dielectric loading attached to the side of the open geometry of the confocal waveguide. The improvements to the gyro-TWT system allowed for zero-drive stable operation at currents up to 3 A. The design frequency of 140.0 GHz was successfully amplified with 35 dB circuit gain and a -3 dB bandwidth of 1.2 GHz from a 48 kV, 3 A electron beam with a beam pitch factor of 0.64 and a perpendicular velocity spread of 6%. The gyro-TWT produced 550 W at 140.0 GHz under the same operating conditions. During experimental testing, the pulse length used was 2 microseconds. The performance of the confocal gyro-TWT suggests that it may be a candidate for application to Dynamic Nuclear Polarization (DNP) Nuclear Magnetic Resonance (NMR) experiments. Thesis Supervisor: Richard J. Temkin Title: Senior Research Scientist, Department of Physics

A 140 GHz gyro-amplifier using a confocal waveguide : theory and experimental results

As a part of the plan to deploy a wideband high-power module (HPM) to very high-throughput satellite (VHTS) network systems, Communications and Power Industries LLC (CPI) has been developing a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> -band high-power traveling-wave tube (TWT) amplifier. The power amplifier is designed with a staggered-vane TWT (SVTWT) circuit and a circular beam, operating at beam voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{k}{)} =18$ </tex-math></inline-formula> –20 kV and beam current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{k}{)} =400$ </tex-math></inline-formula> –500 mA with the perveance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.168 \mu \text{P}$ </tex-math></inline-formula> . Within the development program, three prototypes have been built and tested so far—the first two prototypes only include simple features in their circuit configuration, excluding servers and complex tuning elements. The signal amplification process in the novel beam–wave scheme was demonstrated with the first prototype, showing 35 dBm of output power ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{\text {out}}{)}$ </tex-math></inline-formula> with 10–15 dB of small-signal gain and 4 GHz of 1-dB bandwidth (47.2–51.2 GHz). <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{\text {out}} =57$ </tex-math></inline-formula> dBm (500 W) and 24 dB of small-signal gain (SSG) were demonstrated over 4.2 GHz (47.2–51.4 GHz) of 1-dB bandwidth with the second prototype. During the RF test, the tube operated at the continuous wave (CW) mode (100% of duty cycle) with extra external cooling fans. The third prototype is designed with more complex features, including servers, mode anode, and multistage depressed collector (MDC). Its test results showed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{\text {out}} =54$ </tex-math></inline-formula> dBm (250 W) and 24 dB of SSG over 5.2 GHz (47.2–52.4 GHz) of 1-dB bandwidth, running at CW mode with extra external cooling fans. 

Staggered-Vane Traveling-Wave Tube (SVTWT) Amplifier for High-Power V-Band Applications: Design, Fabrication, and Test

Summary form only given, as follows. A new 3D finite element gun and collector modeling code is under development at SAIC in collaboration with industrial partners and National Laboratories. This development program has been designed specifically to address the shortcomings of current simulation and modeling tools. In particular, although there are 3D gun codes that exist today, their ability to address fine scale features is somewhat limited in 3D due to disparate length scales of certain classes of devices. Additionally, features like advanced emission rules, including thermionic Child's law and comprehensive secondary emission models also need attention. The program specifically targets problems classes including gridded-guns, sheet-beam guns, multi-beam devices, and anisotropic collectors. The presentation provides an overview of the program objectives, the approach to be taken by the development team, and a status of the project.

A description of the new 3D electron gun and collector modeling tool: MICHELLE

Summary form only given. Electron beam collection systems variously employed in O-type fast-wave and slow-wave devices such as gyrotrons, gyroklystrons, klystrons, and TWTs must often be carefully designed to avoid potentially undesirable consequences of secondary electron production at the electrode surface(s). An advanced, three-dimensional electron beam design tool, called MICHELLE, is currently undergoing development by a team lead by SAIC under ONR sponsorship. As part of this new effort, an algorithmic representation of a comprehensive model of secondary emission is being developed for this computational tool in order to achieve an accurate beam collection design capability. The secondary emission model separates the emission problem into two macroparticle species: (1) true secondary electrons (SSE) and (2) rediffused (or backscattered) primary electrons (BSE). Each emitted particle species is assigned empirically-based, discrete angular and energy distributions in normalized form, which in turn are dependent upon both the incident particle energy and angle of incidence. Also, provisions for material-specific surface roughness contributions are included in approximate fashion. Algorithms used to capture the secondary emission model will be detailed.

Comprehensive secondary electron emission modeling for simulating e-beam collection in MICHELLE

Summary form only given Three-dimensional (3D) electron guns, focusing channels, and collectors are the trend to improved device performance, and accurate modeling of these devices leads to reductions in development time and costs This includes gridded guns, multibeam guns, sheet beam guns, quadrupole focusing, multibeam collectors, and asymmetrical collectors The new MICHELLE1 2D/3D steady-state and time-domain particle-in-cell (PIC) code that employs electrostatic and now magnetostatic finite-element field solvers In recent years the code has been employed successfully to design and analyze a wide variety of devices that include the above and also ion thrusters In this presentation we will present how MICHELLE has been used to model a variety of devices Two designs in particular are a MM/SMM wave sheet beam gun and a Ka band gun with quadrupole (strong) focusing The design of a sheet beam electron gun is underway at NRL for application to a MM/SMM wave orotron The gun design parameters are for a beam of 3 mm by 40 mum (aspect ratio of 75:1), and a total current of 50-100 mA The smaller of these dimensions is set by the requirement that the beam thickness be smaller than the transverse scale length of Lperp = gammabetalambda/2pi The preliminary gun design utilizes an immersed flow design with a flat rectangular cathode Further results from this design effort will be presented At mm-wavelengths, a key limitation to the peak and average power of vacuum electronics devices stems from the difficulty of control and confinement of high-current density beams In this paper we summarize an ongoing design study of a strong-focusing lattice employing permanent magnet quadrupoles (PMQs) capable of transporting a sub-mm radius electron beam for vacuum electronics applications

Applications of the michelle 2d/3d electron gun and collector code

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A description of the new 3D electron gun and collector modeling tool: MICHELLE

Comprehensive secondary electron emission modeling for simulating e-beam collection in MICHELLE

Applications of the michelle 2d/3d electron gun and collector code