John R Cary
@colorado.edu
Professor Physics
University of Colorado Boulder
RESEARCH INTERESTS
Physics of plasmas, nonlinear dynamics, and electromagnetics
Scopus Publications
Scopus Publications
Valentina Lee, Robert Ariniello, Christopher Doss, Kathryn Wolfinger, Peter Stoltz, Claire Hansel, Spencer Gessner, John Cary, and Michael Litos
AIP Publishing
We present an experimental and simulation-based investigation of the temporal evolution of light emission from a thin, laser-ionized helium plasma source. We demonstrate an analytic model to calculate the approximate scaling of the time-integrated, on-axis light emission with the initial plasma density and temperature, supported by the experiment, which enhances the understanding of plasma light measurement for plasma wakefield accelerator (PWFA) plasma sources. Our model simulates the plasma density and temperature using a split-step Fourier code and a particle-in-cell code. A fluid simulation is then used to model the plasma and neutral density, and the electron temperature as a function of time and position. We then show the numerical results of the space-and-time-resolved light emission and that collisional excitation is the dominant source of light emission. We validate our model by measuring the light emitted by a laser-ionized plasma using a novel statistical method capable of resolving the nanosecond-scale temporal dynamics of the plasma light using a cost-effective camera with microsecond-scale timing jitter. This method is ideal for deployment in the high radiation environment of a particle accelerator that precludes the use of expensive nanosecond-gated cameras. Our results show that our models can effectively simulate the dynamics of a thin, laser-ionized plasma source. In addition, this work provides a detailed understanding of the plasma light measurement, which is one of the few diagnostic signals available for the direct measurement of PWFA plasma sources.
A. F. Habib, G. G. Manahan, P. Scherkl, T. Heinemann, A. Sutherland, R. Altuiri, B. M. Alotaibi, M. Litos, J. Cary, T. Raubenheimer,et al.
Springer Science and Business Media LLC
AbstractElectron beam quality is paramount for X-ray pulse production in free-electron-lasers (FELs). State-of-the-art linear accelerators (linacs) can deliver multi-GeV electron beams with sufficient quality for hard X-ray-FELs, albeit requiring km-scale setups, whereas plasma-based accelerators can produce multi-GeV electron beams on metre-scale distances, and begin to reach beam qualities sufficient for EUV FELs. Here we show, that electron beams from plasma photocathodes many orders of magnitude brighter than state-of-the-art can be generated in plasma wakefield accelerators (PWFAs), and then extracted, captured, transported and injected into undulators without significant quality loss. These ultrabright, sub-femtosecond electron beams can drive hard X-FELs near the cold beam limit to generate coherent X-ray pulses of attosecond-Angstrom class, reaching saturation after only 10 metres of undulator. This plasma-X-FEL opens pathways for advanced photon science capabilities, such as unperturbed observation of electronic motion inside atoms at their natural time and length scale, and towards higher photon energies.
Ahmad Fahim Habib, Thomas Heinemann, Grace G. Manahan, Daniel Ullmann, Paul Scherkl, Alexander Knetsch, Andrew Sutherland, Andrew Beaton, David Campbell, Lorne Rutherford,et al.
Wiley
AbstractPlasma wakefield accelerators offer accelerating and focusing electric fields three to four orders of magnitude larger than state‐of‐the‐art radiofrequency cavity‐based accelerators. Plasma photocathodes can release ultracold electron populations within such plasma waves and thus open a path toward tunable production of well‐defined, compact electron beams with normalized emittance and brightness many orders of magnitude better than state‐of‐the‐art. Such beams will have far‐reaching impact for applications such as light sources, but also open up new vistas on high energy and high field physics. This paper reviews the innovation of plasma photocathodes, and reports on the experimental progress, challenges, and future prospects of the approach. Details of the proof‐of‐concept demonstration of a plasma photocathode in 90° geometry at SLAC FACET within the E‐210: Trojan Horse program are described. Using this experience, alongside theoretical and simulation‐supported advances, an outlook is given on future realizations of plasma photocathodes such as the upcoming E‐310: Trojan Horse‐II program at FACET‐II with prospects toward excellent witness beam parameter quality, tunability, and stability. Future installations of plasma photocathodes also at compact, hybrid plasma wakefield accelerators, will then boost capacities and open up novel capabilities for experiments at the forefront of interaction of high brightness electron and photon beams.
C. E. Doss, R. Ariniello, J. R. Cary, S. Corde, H. Ekerfelt, E. Gerstmayr, S. J. Gessner, M. Gilljohann, C. Hansel, B. Hidding,et al.
American Physical Society (APS)
E. Lanham, J. Cary, D. Main, T. Jenkins, S. Veitzer, D. Smithe, J. Leddy, G. Werner, and S. Kruger
IEEE
Inductively Coupled Plasmas (ICPs) are extensively used for materials processing, particularly in the semiconductor industry [1]. A typical ICP has an external RF antenna that couples power into a low-pressure chamber, forming a plasma. Antennas used for this purpose are typically coils; the electrical current induces an azimuthal electric field in the chamber, heating electrons and ionizing gas through electron-impact collisions. ICPs generally operate at tens of mTorr and can generate plasma densities up to 1×1018 m−3, Simulations of ICPs have been extensively done, typically using fluid-based models for the plasma species and a power deposition profile for the antenna [2]. For lower pressures, the assumptions in these models may break down, necessitating a fully-kinetic approach.
Jesse M. Snelling, Gregory R. Werner, and John R. Cary
IEEE
Large nanoscale vacuum channel transistor (NVCT) arrays are implemented in LTspice. An empirical warm-beam Child-Langmuir (CL) model is used to determine space charge limiting effects on transmitted current. The LTspice NVCT model is simulated in a Colpitts oscillator circuit. These results are compared to an LTspice NVCT model based on experimental measurements of a particular physical device [1]. The warm-beam CL model is used to demonstrate rapid exploration of different array and circuit parameters.
Luke C. Adams, Gregory R. Werner, and John R. Cary
IEEE
A new, efficient method for optimizing NVCT geometry is presented. Previous work has shown how adjoint techniques can compute the shape gradient (i.e., gradient with respect to shape perturbations) of a prescribed-emission electron gun using only two particle-in-cell simulations [5]. This work provides an extension to the case of self-consistent emission in Hamiltonian systems by including external parameters as dynamical variables. The structure of the perturbed Hamilton's equations then yields a simple recipe for the evaluation of the adjoint problem. The adjoint problem can be evaluated as a perturbed and time-reversed version of the original simulation. From this, the full gradient can be extracted. This general approach is used to incorporate the modified emission current into the computed shape gradients, enabling full-device gradient-based optimization.
R. Ariniello, C. E. Doss, V. Lee, C. Hansel, J. R. Cary, and M. D. Litos
American Physical Society (APS)
P. Scherkl, A. Knetsch, T. Heinemann, A. Sutherland, A. F. Habib, O. S. Karger, D. Ullmann, A. Beaton, G. G. Manahan, Y. Xi,et al.
American Physical Society (APS)
Author(s): Scherkl, Paul; Knetsch, Alexander; Heinemann, Thomas; Sutherland, Andrew; Habib, Ahmad Fahim; Karger, Oliver; Ullmann, Daniel; Beaton, Andrew; Kirwan, Gavin; Manahan, Grace; Xi, Yunfeng; Deng, Aihua; Litos, Michael Dennis; OShea, Brendan D; Green, Selina Z; Clarke, Christine I; Andonian, Gerard; Assmann, Ralph; Jaroszynski, Dino A; Bruhwiler, David L; Smith, Jonathan; Cary, John R; Hogan, Mark J; Yakimenko, Vitaly; Rosenzweig, James B; Hidding, Bernhard | Abstract: Modern particle accelerators and their applications increasingly rely on precisely coordinated interactions of intense charged particle and laser beams. Femtosecond-scale synchronization alongside micrometre-scale spatial precision are essential e.g. for pump-probe experiments, seeding and diagnostics of advanced light sources and for plasma-based accelerators. State-of-the-art temporal or spatial diagnostics typically operate with low-intensity beams to avoid material damage at high intensity. As such, we present a plasma-based approach, which allows measurement of both temporal and spatial overlap of high-intensity beams directly at their interaction point. It exploits amplification of plasma afterglow arising from the passage of an electron beam through a laser-generated plasma filament. The corresponding photon yield carries the spatiotemporal signature of the femtosecond-scale dynamics, yet can be observed as a visible light signal on microsecond-millimetre scales.
Gregory R. Werner, Scott Robertson, Thomas G. Jenkins, Andrew M. Chap, and John R. Cary
AIP Publishing
Accelerated Steady-State Electrostatic Particle-in-Cell Simulation of Langmuir Probes Gregory R. Werner,1 Scott Robertson,1 Thomas G. Jenkins,2 Andrew M. Chap,2, 3 and John R. Cary1, 2 1)Center for Integrated Plasma Studies, University of Colorado, Boulder, Colorado 80309, USA 2)Tech-X Corporation, 5621 Arapahoe Avenue Suite A, Boulder, Colorado 80303, USA 3)Currently at AST & Science, 5825 University Research Ct. #2300, College Park, MD 20740, USA
D. Ullmann, P. Scherkl, A. Knetsch, T. Heinemann, A. Sutherland, A. F. Habib, O. S. Karger, A. Beaton, G. G. Manahan, A. Deng,et al.
American Physical Society (APS)
The FACET E-210 plasma wakefield acceleration experiment was built and operated with support from UCLA (US Department of Energy (DOE) contract no. DESC0009914), RadiaBeam Technologies (DOE contract no. DE-SC0009533), and the FACET E200 team and DOE under contract no. DE-AC02-76SF00515. B.H., P.S., A.S., F.A.H., T.H., A.B. were supported by the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme (NeXource, ERC Grant agreement No. 865877). The work was supported by STFC ST/S006214/1 PWFAFEL, EPSRC (grant no. EP/N028694/1). D.L.B. acknowledges support from the US DOE Office of
High Energy Physics under award no. DE-SC0013855. J.R.C. acknowledges support from the National Science Foundation under award no. PHY 1734281. M.D.L acknowledges support from the US DOE Office of High Energy Physics under award no. DE-SC0017906. This
work used computational resources of the National Energy Research Scientific Computing Center, which is supported by DOE DE-AC02-05CH11231, and of the Supercomputing Laboratory at King Abdullah University of Science & Technology (KAUST) in Thuwal, Saudi Arabia.
Thomas G. Jenkins, Gregory R. Werner, and John R. Cary
AIP Publishing
Joseph G. Theis, Gregory R. Werner, Thomas G. Jenkins, and John R. Cary
AIP Publishing
Archana Sampath, Xavier Davoine, Sébastien Corde, Laurent Gremillet, Max Gilljohann, Maitreyi Sangal, Christoph H. Keitel, Robert Ariniello, John Cary, Henrik Ekerfelt,et al.
American Physical Society (APS)
Sources of high-energy photons have important applications in almost all areas of research. However, the photon flux and intensity of existing sources is strongly limited for photon energies above a few hundred keV. Here we show that a high-current ultrarelativistic electron beam interacting with multiple submicrometer-thick conducting foils can undergo strong self-focusing accompanied by efficient emission of gamma-ray synchrotron photons. Physically, self-focusing and high-energy photon emission originate from the beam interaction with the near-field transition radiation accompanying the beam-foil collision. This near field radiation is of amplitude comparable with the beam self-field, and can be strong enough that a single emitted photon can carry away a significant fraction of the emitting electron energy. After beam collision with multiple foils, femtosecond collimated electron and photon beams with number density exceeding that of a solid are obtained. The relative simplicity, unique properties, and high efficiency of this gamma-ray source open up new opportunities for both applied and fundamental research including laserless investigations of strong-field QED processes with a single electron beam.
P. H. Stoltz, J. W. Luginsland, A. Chap, D. N. Smithe, and J. R. Cary
AIP Publishing
Many high power electronic devices operate in a regime where the current they draw is limited by the self-fields of the particles. This space charge limited current poses particular challenges for numerical modeling where common techniques like over-emission or Gauss' Law are computationally inefficient or produce nonphysical effects. In this paper, we show an algorithm using the value of the electric field in front of the surface instead of attempting to zero the field at the surface, making the algorithm particularly well suited to both electromagnetic and parallel implementations of the particle-in-cell algorithm. We show how the algorithm is self-consistent within the framework of finite difference (for both electrostatics and electromagnetics). We show several 1D and 2D benchmarks against both theory and previous computational results. Finally, we show the application in 3D to high power microwave generation in a 13 GHz magnetically insulated line oscillator.
C. E. Doss, E. Adli, R. Ariniello, J. Cary, S. Corde, B. Hidding, M. J. Hogan, K. Hunt-Stone, C. Joshi, K. A. Marsh,et al.
American Physical Society (APS)
We present a laser-ionized, beam-driven, passive thin plasma lens that operates in the nonlinear blowout regime. This thin plasma lens provides axisymmetric focusing for relativistic electron beams at strengths unobtainable by magnetic devices. It is tunable, compact, and it imparts little to no spherical aberrations. The combination of these features make it more attractive than other types of plasma lenses for highly divergent beams. A case study is built on beam matching into a plasma wakefield accelerator at SLAC National Accelerator Laboratory’s FACET-II facility. Detailed simulations show that a thin plasma lens formed by laser ionization of a gas jet reduces the electron beam’s waist beta function to half of the minimum value achievable by the FACET-II final focus magnets alone.
A. Deng, O. S. Karger, T. Heinemann, A. Knetsch, P. Scherkl, G. G. Manahan, A. Beaton, D. Ullmann, G. Wittig, A. F. Habib,et al.
Springer Science and Business Media LLC
Plasma waves generated in the wake of intense, relativistic laser1,2 or particle beams3,4 can accelerate electron bunches to gigaelectronvolt energies in centimetre-scale distances. This allows the realization of compact accelerators with emerging applications ranging from modern light sources such as the free-electron laser to energy frontier lepton colliders. In a plasma wakefield accelerator, such multi-gigavolt-per-metre wakefields can accelerate witness electron bunches that are either externally injected5,6 or captured from the background plasma7,8. Here we demonstrate optically triggered injection9–11 and acceleration of electron bunches, generated in a multi-component hydrogen and helium plasma employing a spatially aligned and synchronized laser pulse. This ‘plasma photocathode’ decouples injection from wake excitation by liberating tunnel-ionized helium electrons directly inside the plasma cavity, where these cold electrons are then rapidly boosted to relativistic velocities. The injection regime can be accessed via optical11 density down-ramp injection12–16 and is an important step towards the generation of electron beams with unprecedented low transverse emittance, high current and 6D-brightness17. This experimental path opens numerous prospects for transformative plasma wakefield accelerator applications based on ultrahigh-brightness beams.Electron bunches are generated and accelerated to relativistic velocities by tunnel ionization of neutral gas species in a plasma. This represents a step towards ultra-bright, high-emittance beams in laser-plasma accelerators.
M. D. Litos, R. Ariniello, C. E. Doss, K. Hunt-Stone, and J. R. Cary
The Royal Society
A current challenge that is facing the plasma wakefield accelerator (PWFA) community is transverse beam emittance preservation. This can be achieved by balancing the natural divergence of the beam against the strong focusing force provided by the PWFA plasma source in a scheme referred to as beam matching. One method to accomplish beam matching is through the gradual focusing of a beam with a plasma density ramp leading into the bulk plasma. Here, the beam dynamics in a Gaussian plasma density ramp are considered, and an empirical formula is identified that gives the ramp length and beam vacuum waist location needed to achieve near-perfect matching. The method uses only the beam vacuum waist beta function as an input. Numerical studies show that the Gaussian ramp focusing formula is robust for beta function demagnification factors spanning more than an order of magnitude with experimentally favourable tolerances for future PWFA research facilities. This article is part of the Theo Murphy meeting issue ‘Directions in particle beam-driven plasma wakefield acceleration’.
N. Crossette, T. G. Jenkins, J. R. Cary, J. Leddy, and D. N. Smithe
IEEE
In 1963, L. M. Chanin and G. D. Rork [Phys. Rev. 133, A1005 (1964)] [1] measured the first Townsend ionization coefficient for various gases and a range of pressures experimentally in a vacuum tube. A Townsend discharge is an ionization avalanche that occurs between two electrodes when secondary electron emission caused by ion impact on the cathode is negligible. The first Townsend coefficient, α, is essentially a measure of how many ionization events a single electron will cause when subject to a uniform electric field. In this study, we reproduce the experimental setup of Chanin and Rork's device in VSim [C. Nieter and J. R. Cary, J. Comp. Phys. 196, 448 (2004)] [2], a highly parallelized particle-in-cell/finite-difference time-domain code. Various particle interactions are included, and the first Townsend coefficient is calculated and compared to the reported value.
T. G. Jenkins, A. M. Chap, G. R. Werner, and J. R. Cary
IEEE
Speed-limited particle-in-cell (SLPIC) modeling is a new simulation technique [G. R. Werner et al., Phys. Plasmas 25,123512 (2018)], potentially much faster than conventional PIC, for modeling plasmas characterized by low-velocity kinetic processes. Numerical constraints (e.g. timestep limitations associated with particle cell-crossing times or stability limits) often place challenging restrictions on PIC models of these plasmas; even though the kinetic physics of interest predominantly involves slow particles, the fastest particles dictate the maximum allowable timestep. For high-Z plasmas, large ion/electron mass ratios separate the species timescales to the point that kinetic simulation may be prohibitive, and computational costs can be high even in hydrogenic plasmas. SLPIC provides a possible solution. SLPIC (like PIC) retains a fully kinetic description of the plasma, but imposes an artificial speed limit on fast particles whose kinetics do not play a meaningful role in the system dynamics. Larger simulation timesteps, which enable faster simulations of such discharges, are thus permitted. The speed-limiting is done in a mathematically rigorous sense to maintain accuracy over longer timescales; we may, for instance, speed-limit the bulk of the electron distribution to evolve only on characteristic ion timescales (and use larger simulation timesteps, which need only resolve these scales, to simulate the discharge). In this paper we'll demonstrate the use of SLPIC methods using the VSim code [C. Nieter and J. R. Cary, J. Comp. Phys. 196, 448 (2004)], moving from simple models of collisionless sheath formation (for which SLPIC has achieved >260x overall speedup relative to PIC with comparable accuracy) to discuss SLPIC applications in more general low-temperature plasma discharges (e.g. collisional plasmas). We'll also discuss prospects for using SLPIC in the rapid modeling of plasma discharge evolution through transient or fluid-like phases, and its capability to transition mid-simulation to a smaller-timestep conventional PIC model as kinetic processes in the discharge become important.
R. Ariniello, C. E. Doss, K. Hunt-Stone, J. R. Cary, and M. D. Litos
American Physical Society (APS)
Gregory R. Werner, Thomas G. Jenkins, Andrew M. Chap, and John R. Cary
AIP Publishing
Based on the particle-in-cell (PIC) plasma simulation method, the speed-limited PIC (SLPIC) method delivers faster kinetic plasma simulation in cases where the particle distributions evolve slowly compared with the maximum stable PIC timestep. SLPIC thus offers more feasible, fully kinetic simulation in regimes that historically have required fluid approaches, such as magnetohydrodynamic (MHD), two-fluid, or Boltzmann electron treatments. In particular, SLPIC allows an explicit time advance with steps much larger than the inverse plasma frequency, avoiding the instability explicit PIC faces with large timesteps. SLPIC avoids this instability by slowing down fast particles (e.g., electrons) in a way that is rigorously underpinned by an approximate Vlasov equation; unlike MHD, two-fluid, and Boltzmann electron approaches, SLPIC does not fundamentally neglect any first-principles plasma physics, although the choices of grid cell size, timestep, and number of macroparticles per cell naturally limit the physical phenomena that can be accurately represented. SLPIC can be implemented with minor modifications of a standard PIC code and does not require an implicit time advance. It enables large timesteps in first-principles kinetic plasma simulation of appropriately slow phenomena, and it can handle many of the same complications as PIC, such as boundary conditions and collisions. In an argon plasma sheath test problem, a SLPIC simulation achieved a speed-up of a factor of 160 over the corresponding PIC simulation, without loss of accuracy.
Micha Litos, Robert Ariniello, Christopher Doss, Keenan Hunt-Stone, and John R. Cary
IEEE
The ion channel laser (ICL) was originally proposed as a compact, plasma-based alternative to the free electron laser (FEL) [1]. It is, in many ways, analogous to the FEL, though it offers some distinct advantages all on its own. Most notably, the ICL can accommodate a larger electron energy spread, making it better suited for high-brightness plasma-injected beams. In addition, the same radiator (plasma source) can be used to produce elliptically polarized light without alteration, a feature that is absent in an FEL. Historically, electron beam quality and plasma source development were insufficient for the demonstration of the ICL. In addition, the ICL appeared unfavorable due to the inherently short Rayleigh length of the radiation it produced. Recent literature, however, has shown that high gain can be achieved, despite the short Rayleigh length [2]. In addition, current and near-future facilities are able to provide appropriate beams and plasma sources for the ICL. Experimental opportunities to demonstrate an ICL at the Facility for Advanced Accelerator Experimental Tests II (FACET-II) are presented, utilizing both a 10 GeV beam originating from the SLAC National Accelerator Laboratory linac, and a 1 GeV high-brightness, plasma-injected beam.
Isabella Pagano, Jason Brooks, Aaron Bernstein, Rafal Zgadzaj, Jarrod Leddy, John Cary, and Michael C. Downer
IEEE
We simulate the possibility of scaling channel formation to low densities plasmas of low atomic number gas over a large range of pulse duration including (1) pulses up to 300 ps in duration, using inverse bremsstrahlung (IB) heating and (2) ultrashort pulses up to 100s of femtoseconds for generating tenuous plasmas of centimeter to meter lengths by optical field ionization (OFI) [1]. Results show IB heating up to tens of eV, and channels formed from an initial density of 1×10<sup>18</sup> cm<sup>−3</sup> with axial densities as low as 1×10<sup>17</sup> cm<sup>−3</sup>, and radius of 50 μm. It has been shown that centimeter-scale waveguides can be generated via OFI heating at densities of approximately 1×10<sup>17</sup> cm<sup>−3</sup>[2]; we show calculations and theory of this channel formation using an axicon. Lastly, we outline the experimental setup to be used in future experiments at the University of Texas Tabletop Terawatt (UT3) facility.
Nate P. Crossette, Thomas G. Jenkins, David N. Smithe, and John R. Cary
IEEE
Plasma Vapor Deposition (PVD) is used in a variety of industrial applications for coating thin films over a substrate. In the PVD process within magnetron sputtering devices, electrons ionize a background gas and the ensuing ions, accelerated by a potential gradient, strike a target cathode and sputter off neutral atoms. The sputtered material travels ballistically, interacting with the plasma through collisions or depositing on a surface within the chamber.1