Serguei Ovtchinnikov

Modeling emission lag after photoexcitation

A theoretical model of delayed emission following photoexcitation from metals and semiconductors is given. Its numerical implementation is designed for beam optics codes used to model photocathodes in rf photoinjectors. The model extends the Moments approach for predicting photocurrent and mean transverse energy as moments of an emitted electron distribution by incorporating time of flight and scattering events that result in emission delay on a sub-picosecond level. The model accounts for a dynamic surface extraction field and changes in the energy distribution and time of emission as a consequence of the laser penetration depth and multiple scattering events during transport. Usage in the Particle-in-Cell code MICHELLE to predict the bunch shape and duration with or without laser jitter is given. The consequences of delayed emission effects for ultra-short pulses are discussed.

High performance parametric design optimization of RF devices

We present an integrated environment for large scale multi-parameter design optimization of RF devices based on AFRLs Galaxy Simulation Builder productivity tool for distributed high-performance computing, Sandia National Labs DAKOTA optimization library, and a suite of highly efficient GPU-based Electromagnetic codes developed at NRL in collaboration with Leidos, Inc. The environment allows for an end-to-end optimization cycle of an RF device to be set up, deployed, carried out, monitored and analyzed in a quick, user-friendly, robust, and flexible fashion using a diverse variety of high-end parallel computing resources.

Developments in parallelization and the user environment of the MICHELLE charged particle beam optics code

The next generation of the MICHELLE ES PIC code is to improve its parallelization and leverages a number of existing and emerging DOD HPC architectures and software including distributed memory clusters, multicore, and computational accelerators such as GPUs and Intel Xeon Phi co-processors. The ongoing project supported by the DOD HASI program also aims to build interfaces between MICHELLE and existing HPC tools such as CAPSTONE, GSB, ParaView, and VisIt for efficient design and optimization workflow. This paper reports on the latest progress and discusses applicable algorithms and implementations.

A high-performance distributed computing framework for parametric design optimization of RF devices

The design cycle of RF devices is greatly facilitated by the use of the “virtual prototyping” methodology based on high-fidelity computer simulations that are capable of predicting the RF devices performance in response to changes in its physical parameters. In particular, critical dimensions of the structure, or quantitative properties of the various electromagnetic components are routinely utilized in sensitivity analyses coupled with performance optimization. This type of process is well suited to semi-supervised global optimization. To this end we have integrated our RF simulation codes with several existing software tools for optimization and distributed high-performance computing code deployment and management, such as the DAKOTA toolkit [1], and AFRLs Galaxy Simulation Builder (GSB).

Vacuum electronic device design using 3D EM-PIC

We present new capabilities introduced in the 3D Electromagnetic Particle-in-Cell code Neptune to directly support rapid simulation-based design of a broad range of vacuum electronic devices.

Modeling high average current and high bunch charge beams in MICHELLE-eBEAM

The MICHELLE-eBEAM code has been employed successfully for modeling high average current and high bunch charge beams using a time-dependent model. Accurate particle tracking with self-consistent space charge and image forces is important in modeling detailed phase space evolution of high charge electron bunches. The MICHELLE-eBEAM code presents a promising solution where the model resolution only depends on the number of particles modeled and the detailed phase space evolution is enabled by accurate Coulomb calculations facilitated by a GPU-based tree algorithm. In this paper we report on our latest progress and show validation and benchmarking results.

RF amplifier design using 3D EM-PIC

Summary form only given. The 3D Electromagnetic Particle-in-Cell (EM-PIC) algorithm provides a powerful method to predict performance of RF amplifiers based on actual device geometry and defined operating parameters. Until recently its utility as a primary design tool has been restricted by long simulation times or limited accuracy, due to computational and/or algorithmic constraints of available implementations. Advances in the representation of geometry using conformal techniques, coupled with highly parallel implementations of the EM-PIC algorithm, have made EM-PIC viable as a primary design tool. The EM-PIC code Neptune1, 2 exploits highly parallel GPU hardware in conjunction with conformal geometry representation to perform fast, accurate amplifier simulations. It is now a primary tool at NRL for the design and simulation of single- and multi-stage TWT amplifiers (serpentine waveguide, folded waveguide, helix, transverse TWT), klystrons and EIK amplifiers, and has enabled new research into advanced device concepts including cascaded multi-beam TWTs and transverse-interaction TWT amplifiers. We report on recent additions to Neptunes algorithms that directly support the needs of RF amplifier design. First, a new method to improve the discretization accuracy for dielectric regions will be demonstrated, based on a novel subcell averaging scheme. Second, we report on a range of new features supporting device design. New particle beam and magnetic field import facilities allow interfacing with complementary design tools, including the gun/collector code MICHELLE3, while new diagnostics for RF current and beam interception allow detailed monitoring of device operation.

Counter streaming charged particle beam model in MICHELLE-Ebeam

Summary form only given. Reported on is the progress of the counter streaming, fully self-consistent model development in the MICHELLE Ebeam [1,2,3] code. This GPU-based software module performs high accuracy simulations of electron and ion beams including the effects of stochastic space charge.

Status of the MICHELLE code and applications to RF guns

Summary form only given. The MICHELLE two-dimensional (2D) and three-dimensional (3D) steady-state and time-domain particle-in-cell (PIC) code has been employed successfully by industry, national laboratories, and academia and has been used to design and analyze a wide variety of devices, including RF photoemitters, RF gated emitters, multistage depressed collectors, gridded guns, multibeam guns, annular-beam guns, sheet-beam guns, beam-transport sections, and ion thrusters.