About

John Cary is a professor in the Department of Physics at the University of Colorado Boulder. His research focuses on plasma and accelerator physics, with particular emphasis on nonlinear dynamics and advanced computational methods, including massively parallel and object-oriented approaches. His work involves applications to accelerator lattices and instabilities, advanced acceleration concepts, transport in fusion plasma confinement systems, and plasma turbulence.

Research topics

• Nuclear physics
• Physics
• Atomic physics
• Optics

Selected publications

• Pressure dependence of magnetron sputtering: 2D-RZ particle-in-cell and 1D fluid modeling

  Physics of Plasmas · 2026-05-01

  articleOpen accessSenior author

  We reproduce the consistently-seen experimental voltage vs pressure (V–p) dependence of DC magnetron sputtering with two-dimensional-RZ particle-in-cell (PIC) simulation. Informed by PIC simulation, we develop a steady-state, 1D-axial fluid model of the sheath and presheath that also reproduces this V–p dependence. The V–p dependence is the relationship between the steady-state voltage needed to maintain a constant discharge current and the neutral gas pressure. V–p dependence is fundamental to device performance, but has not previously been reproduced with simulation or satisfactorily explained. We find that the decrease in voltage with increasing pressure is not due to electron recapture at the cathode. Rather, the constant current dictates a constant global ionization rate, so the voltage decrease compensates for the increase in neutral gas density by lowering the energy of the plasma electrons, which decreases their ionization probability. The PIC simulations also reveal that the presheath and bulk plasma are unaffected by the electron reflection coefficient at the cathode; the only effect of increasing reflection is a reduction in the sheath voltage and width. In addition to the potential structure, we explore how pressure affects the plasma density, particle drifts, and particle energy distributions.

  PublisherDOI

• Modeling the role of secondary electron emission in direct current magnetron sputtering using explicit energy-conserving particle-in-cell methods

  Physics of Plasmas · 2026-02-01 · 2 citations

  articleOpen access

  We present results from particle-in-cell (PIC) simulations of direct current magnetron sputtering (dcMS) in a 2D cylindrically symmetric geometry. The PIC model assumes an electrostatic approximation and includes the Monte Carlo collision method to model collisions between electrons and the neutral gas. A newly implemented explicit energy-conserving PIC algorithm (EC-PIC) is also exercised by the model, and results are compared with the standard momentum-conserving PIC (MC-PIC) method. We use these simulation tools to examine how changes in ion-induced secondary electron yield (SEY) and the external circuit impact the steady-state current, voltage, and plasma density of dcMS discharges. We show that in general, higher ion-induced SEY and lower external resistance values lead to larger currents, smaller voltages, and larger plasma densities. Simulation results presented in this paper related to the ion-induced SEY demonstrate similar trends that have been observed in previous experimental work and theory. Finally, we demonstrate that EC-PIC maintains numerical stability up to cell sizes as large as ten times the electron Debye length. While we have not performed a comprehensive stability study of MC-PIC, this paper demonstrates improved stability over the standard practice often assumed in MC-PIC. We therefore demonstrate that EC-PIC allows for modeling a wide range of plasma currents and densities using modest computational resources compared with PIC models that require resolution of the electron Debye length.

  PublisherDOI

• Modeling the Role of Secondary Electron Emission in Direct Current Magnetron Sputtering using Explicit Energy-Conserving Particle-in-Cell Methods

  ArXiv.org · 2025-07-14

  preprintOpen access

  We present results from a fully kinetic particle-in-cell (PIC) simulation of direct current magnetron sputtering (dcMS) in a 2D cylindrically symmetric geometry. The particle-in-cell model assumes an electrostatic approximation and includes the Monte Carlo collision (MCC) method to model collisions between electrons and the neutral gas. A newly-implemented explicit energy-conserving PIC algorithm (EC-PIC) is also exercised by the model and results are compared with the standard momentum conserving PIC (MC-PIC) method. We use these simulation tools to examine how changes in secondary electron yield (SEY) and the external circuit impact the steady-state current, voltage, and plasma density of dcMS discharges. We show that in general, higher SEY and lower external resistance values lead to larger currents, smaller voltages, and larger plasma densities. We demonstrate that EC-PIC is superior to MC-PIC as the plasma current and density increase due to the improved numerical stability provided by EC-PIC.

  PublisherOA PDFDOI

• Labor Market Survey/Research: An Approach Centered on the Individual and Grounded in Objective and Reliable Data

  The Rehabilitation Professional · 2025-11-09

  articleOpen access1st authorCorresponding

  In 2010, a cross section of Vocational Rehabilitation Counselors (VRC’s) in Washington State took part in a comprehensive review oflabor market survey methodology as it pertains to Washington Administrative Codes (WAC) (Donley & Johnson, 2015). This review produced the Labor Market Survey/Research (LMS/R) protocol: a combination of quantitative and qualitative data derived from scientifically surveyed published statistics and individual employer sampling, analyzed against worker-specific data, to arrive at a valid vocational opinion (Donley & Johnson, 2013). The goal is to arrive at a reliable conclusion based on these factors and VRC’s professional clinical judgment (Barros-Bailey & Heitzman, 2014; Field, Choppa, & Weed, 2009). This article will review the LMS/R protocol as an option when conducting labor market research.

  PublisherOA PDFDOI

• Grid instability growth rates for explicit, electrostatic momentum- and energy-conserving particle-in-cell algorithms

  Physics of Plasmas · 2025-09-01 · 1 citations

  articleOpen accessSenior author

  When the Debye length is not resolved in a simulation using the most common particle-in-cell (PIC) algorithm, the plasma will unphysically heat until the Debye length becomes resolved via a phenomenon known as grid heating. This paper presents detailed numerical measurements of grid heating for several explicit PIC algorithms, including the first systematic (covering the Debye length resolution and drift-velocity parameter space) study of grid-heating growth rates for the most common electrostatic momentum-conserving PIC algorithm. Additionally, we derive and test a cubic-spline-based PIC algorithm that ensures that the interpolated electric field has a continuous first derivative but find that a differentiable electric field has minimal impact on grid-heating stability. We also considered energy-conserving PIC algorithms with linear and quadratic interpolation functions. In all cases, we find that unphysical heating can occur for some combinations of Debye under-resolution and plasma drift. We demonstrate analytically and numerically that grid heating cannot be eliminated by using a higher-order field solve and give an analytical expression for the cold-beam stability limits of some energy-conserving algorithms.

  PublisherDOI

• Performing a Review of Past Medical Bills to Determine the Reasonableness of Costs

  Journal of Life Care Planning · 2025-12-01

  articleOpen access

  Through their work developing and implementing life care plans, life care planners have routine exposure to costs associated with the ongoing care of individuals with disabilities. This work encompasses a wide range of services, including but not limited to routine medical care, diagnostic tests, therapeutic modalities, medical procedures and surgical interventions, medications, transportation, household services, case management and vocational services. When combined, published professional standards of practice, peerreviewed generally accepted methodology, and recurring exposure to actual costs for services, provide a foundation for opinion and testimony regarding the reasonableness of past medical charges and future costs.

  PublisherOA PDFDOI

• Kinetic simulations of low-temperature plasmas used for plasma processing: ICP and feature-scale models

  2025-04-22

  articleSenior author

  Low-temperature kinetic plasma simulations using Particle-in-Cell (PIC) and Monte Carlo methods (DSMC/MCC) for the chemistry can provide many advantages over fluid simulations, including detailed information about the Ion Energy Distribution Function (IEDF) and Ion Angular Distribution Function (IADF) that are critical for plasma processing. In this presentation, two different types of simulations illustrating the advantages of kinetic modeling are demonstrated. The first is a macroscopic-scale simulation of an Inductively Coupled Plasma (ICP). We demonstrate how implicit methods can make these challenging simulations feasible, and how process parameters such as neutral gas density and bias frequency affect the IEDF and IADF at the wafer surface. We also demonstrate a method of providing constant power to the plasma which decreases run-times to reach steady state and examine the steady-state ion fluxes and IEDFs/IADFs incident on the wafer as a function of bias frequency and waveform shape. Secondly, we discuss efforts to develop microscopic feature-scale simulation capabilities, e.g. for through-silicon vias or other high-aspect-ratio etch features wherein the trajectories of etching species may be affected by charge accumulation on feature sidewalls. Here, our recent efforts have focused on the development of self-consistent flux boundary conditions from macroscopic (sheath)-scale simulations that can be used as inputs for such feature-scale simulations.

  PublisherDOI

• Nonlocal effects on thermal transport in hydrodynamic simulations of unmagnetized MagLIF-relevant gaspipes on NIF

  Physics of Plasmas · 2025-08-01 · 1 citations

  articleOpen accessSenior author

  We present simulations of heat flow relevant to gaspipe experiments on the National Ignition Facility to investigate kinetic effects on transport phenomena. D2 and neopentane (C5H12) filled targets are used to study the laser preheat stage of a MagLIF scheme where an axial magnetic field is sometimes applied to the target. Simulations were done with the radiation-MHD code HYDRA with a collision-dominated fluid model and the SNB nonlocal electron thermal conduction model. Using the SNB model to evolve the electron temperature increased the heat front propagation of neopentane gas targets compared to a local model by limiting radial heat flow. This increases electron temperature near the axis, which decreases laser absorption. We find that the effect of heat flow models on temperature profiles and laser propagation is modest. Beyond the SNB model, we utilize HYDRA to initialize plasma conditions for the Vlasov–Fokker–Planck K2 code. We run K2 until a quasi-steady state is reached and examine the impact of kinetic effects on heat transport. Although axial heat flow is well predicted by fluid models, the fluid model consistently overpredicts radial heat flow up to 150% in regions with the largest temperature gradient of D2 filled gaspipes. On the other hand, the SNB nonlocal electron conduction model is found to be adequate for capturing kinetic heat flow in gaspipes.

  PublisherDOI

• Nonlocal effects on Thermal Transport in MagLIF-Relevant Gaspipes on NIF

  ArXiv.org · 2025-04-12

  articleOpen accessSenior author

  We present simulations of heat flow relevant to gaspipe experiments on the National Ignition Facility (NIF) to investigate kinetic effects on transport phenomena. D2 and neopentane (C5H12) filled targets are used to study the laser preheat stage of a MagLIF scheme where anaxial magnetic field is sometimes applied to the target. Simulations were done with the radiation-MHD code HYDRA with a collision-dominated fluid model and the Schurtz nonlocal electron thermal conduction model. Using the Schurtz model to evolve the electron temperature increased the heat front propagation of neopentane gas targets compared to a local model by limiting radial heat flow. This increases electron temperature near the axis, which decreases laser absorption. We find the effect of heat flow models on temperature profiles and laser propagation is modest. Beyond the Schurtz model, we utilize HYDRA to initialize plasma conditions for the Vlasov Fokker-Planck K2 code. We run K2 until a quasi-steady state is reached and examine the impact of kinetic effects on heat transport. Although axial heat flow is well predicted by fluid models, the fluid model consistently over predicts radial heat flow up to 150% in regions with the largest temperature gradient of D2 filled gaspipes. On the other hand, the Schurtz nonlocal electron conduction model is found to be adequate for capturing kinetic heat flow in gaspipes.

  PublisherOA PDFDOI

• A Walk-Through From Referral to Testimony: Methodology & Admissibility

  Journal of Life Care Planning · 2025-12-01

  articleOpen access1st authorCorresponding

  The focus of this paper is to address the issue of rehabilitation professionals having their credibility and the admissibility of their opinions challenged when called to testify in litigation matters, and how rehabilitation professionals should adhere to proper methodology that reflects their day-to-day clinical work. The objectives of this paper are to identify what qualifies rehabilitation professionals to provide opinions to the court, to discuss subjects of credibility often raised in a deposition and at trial, and how to address these subjects from various perspectives. Beginning at the point of referral and moving through the full spectrum of an assessment (i.e. clinical interview, testing, research, consultations, and report writing), the authors discuss effectively defending the relevance and admissibility of their opinions in a deposition and at trial. This paper covers the following topics: clinical practice, methodology, court rules, and the line between professional style, professional preference, and admissible practices.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Preformed Laser-driven Plasma Waveguides for Multi-GeV Laser-Plasma Electron Acceleration

  NSF · $304k · 2017–2023

Frequent coauthors

• Wim Leemans

  Deutsches Elektronen-Synchrotron DESY

  222 shared

• David Bruhwiler

  179 shared

• C. B. Schroeder

  172 shared

• E. Cormier‐Michel

  Tech-X Corporation (United States)

  126 shared

• C. G. R. Geddes

  109 shared

• Eric Esarey

  108 shared

• E. Esarey

  106 shared

• G. Werner

  University of Colorado Boulder

  94 shared

Labs

• The Center for Integrated Plasma StudiesPI

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