Showing 1–26 of 26 results for author: Cook, M

Investigation of GeSn aspect ratio trapping growth up to 8% Sn

Authors: Hryhorii Stanchu, Quang Minh Thai, Fernando M. de Oliveira, Mourad Benamara, Stephen Margiotta, Matthew Cook, Xiaoxin Wang, Jifeng Liu, Perry C. Grant, Baohua Li, Wei Du, Gregory Salamo, Shui-Qing Yu

Abstract: Aspect ratio trapping (ART) growth of germanium-tin (GeSn) is a promising approach to target important objectives on the quest towards commercialization of complementary metal-oxide-semiconductor (CMOS)-compatible GeSn optoelectronics devices. Its local growth on patterned substrate allows for versatile device integration into photonics integrated circuit or for stand-alone structure like focal pl… ▽ More Aspect ratio trapping (ART) growth of germanium-tin (GeSn) is a promising approach to target important objectives on the quest towards commercialization of complementary metal-oxide-semiconductor (CMOS)-compatible GeSn optoelectronics devices. Its local growth on patterned substrate allows for versatile device integration into photonics integrated circuit or for stand-alone structure like focal plane array imager. Additionally, high aspect ratio from nano-sized window can terminate early threading dislocation propagation on the oxide sidewalls, leaving subsequent growth defect-free and potentially improving the device performance. Knowledge remains missing regarding GeSn ART growth kinetics, morphology and how they evolve from thin film growth, with successful growth itself yet to be demonstrated. In this work, we report GeSn ART growth up to 8% Sn. Two configurations -- self-induced Ge core/GeSn shell for Sn content between 6% and 8%, and bulk GeSn ART for Sn content below 1% -- are observed. We present a comprehensive study on GeSn ART growth kinetics through different growth rounds and designs, showing a link between pyramid shape of ART island and successful Sn incorporation, as well as the role of growth selectivity and local heating. △ Less

Submitted 3 August, 2026; originally announced August 2026.

Study of GeSn Selective Area Growth with Demonstration of SWIR Light Detection

Authors: Hryhorii Stanchu, Quang Minh Thai, Rajesh Kumar, Fernando M. de Oliveira, Kushal Dahal, Xuehuan Ma, Sudip Acharya, Justin Rudie, Alexander Golden, Joshua M Grant, Matthew Cook, Stephen Margiotta, Xiaoxin Wang, Jifeng Liu, Perry C. Grant, Baohua Li, Wei Du, Gregory Salamo, Shui-Qing Yu

Abstract: As germanium-tin (GeSn) epitaxial growth quality continuously improves, the search for an efficient integration strategy of GeSn optoelectronics devices into complementary metal-oxide-semiconductor (CMOS) manufacturing line also accelerates. Selective area growth (SAG) on patterned substrate emerges as a promising approach for this quest, with locally controlled growth of GeSn laser/detector suita… ▽ More As germanium-tin (GeSn) epitaxial growth quality continuously improves, the search for an efficient integration strategy of GeSn optoelectronics devices into complementary metal-oxide-semiconductor (CMOS) manufacturing line also accelerates. Selective area growth (SAG) on patterned substrate emerges as a promising approach for this quest, with locally controlled growth of GeSn laser/detector suitable for either co-integration with silicon-based waveguide structure or stand-alone module like focal plane array. In this work, we report successful GeSn SAG with Sn content ranging from 3.2% to 8.7% of good optical quality, with demonstration of tunable GeSn SAG photoluminescence and GeSn SAG photoconductor device, the latter with detection cutoff wavelength up to 2 um. In addition, we present a comprehensive study of GeSn SAG condition at different window sizes, from 2 um to 100 um, and shapes: circle, square, octagon, and rectangle. Presence of loading effect is revealed, where GeSn growth rate increases as pattern fill factor and window size shrink. It introduces a different growth condition compared to thin film growth, which can weaken or inhibit Sn incorporation at very small window size and induce Sn segregation in high Sn content SAG growth. △ Less

Submitted 17 July, 2026; originally announced July 2026.

COMBUST: Gridded combustible mass estimates of the built environment in the conterminous United States (1975-2020)

Authors: Johannes H. Uhl, Maxwell C. Cook, Cibele Amaral, Stefan Leyk, Jennifer K. Balch, Alan Robock, Owen B. Toon

Abstract: The increasing occurrence of natural hazards such as wildfires and drought, along with urban expansion and land consumption, causes increasing levels of fire risk to populations and human settlements. Moreover, increasing geopolitical instability in many regions of the world requires evaluation of scenarios related to potential hazards caused by military operations. Quantitative knowledge on burna… ▽ More The increasing occurrence of natural hazards such as wildfires and drought, along with urban expansion and land consumption, causes increasing levels of fire risk to populations and human settlements. Moreover, increasing geopolitical instability in many regions of the world requires evaluation of scenarios related to potential hazards caused by military operations. Quantitative knowledge on burnable fuels and their spatio-temporal distribution across landscapes is crucial for risk and potential damage assessments. While there is good understanding of the distributions of biomass fuels based on remote sensing observations, the combustible mass of the built environment has rarely been quantified in a spatially explicit manner. Therefore, we developed fine-grained estimates of urban fuels for the conterminous United States, estimating the combustible mass of building materials, building contents, and personal vehicles at 250 m spatial resolution. The resulting dataset is called COMBUST (Combustible mass of the built environment in the conterminous United States) and includes different backcasting scenarios from 1975 to 2020. COMBUST is based on the integration of a variety of geospatial data sources such as Earth-observation derived data, real estate data, statistical estimates and volunteered geographic information. COMBUST is accompanied by COMBUST PLUS, a set of consistently enumerated gridded datasets facilitating combustion exposure modelling of buildings and population. These datasets constitute a rich resource for ecological and social science applications, as well as for disaster risk management and planning-related decision making for U.S. settlements. COMBUST is available at https://doi.org/10.5281/zenodo.15611963. △ Less

Submitted 11 November, 2025; originally announced November 2025.

Efficient ion re-acceleration in laboratory-produced interpenetrating collisionless shocks

Authors: W. Yao, I. Cohen, P. Suarez Gerona, H. Ahmed, A. F. A. Bott, S. N. Chen, M. Cook, R. Lelièvre, P. Martin, T. Waltenspiel, P. Antici, J. Béard, M. Borghesi, D. Caprioli, A. Ciardi, E. d'Humières, M. François, L. Gremillet, A. Marcowith, M. Miceli, T. Seebaruth, S. Orlando, J. Fuchs

Abstract: Although the origin of cosmic rays (CRs) remains an open question, collisionless magnetized shock waves are widely regarded as key sites for particle acceleration. Recent theories further suggest that shock-shock collisions in stellar clusters could provide the additional acceleration needed to explain the observed high-energy CR spectrum. Here, we investigate this hypothesis through a laser-based… ▽ More Although the origin of cosmic rays (CRs) remains an open question, collisionless magnetized shock waves are widely regarded as key sites for particle acceleration. Recent theories further suggest that shock-shock collisions in stellar clusters could provide the additional acceleration needed to explain the observed high-energy CR spectrum. Here, we investigate this hypothesis through a laser-based experiment that creates magnetized plasma conditions similar to astrophysical environments. Our results demonstrate that interpenetrating collisionless shocks can significantly boost the energy of ambient protons previously energized by the individual shocks, while also improving the overall acceleration efficiency. Numerical kinetic simulations corroborate these findings, revealing that protons are reaccelerated via their bouncing motion in the convective electric fields of the colliding magnetized flows. By allowing to highly energize ambient protons, our novel colliding-shock platform opens the prospect to test the long-discussed mechanism of diffusive shock acceleration in a controlled laboratory setting. △ Less

Submitted 26 June, 2026; v1 submitted 27 August, 2025; originally announced August 2025.

SPLENDOR: a novel detector platform to search for light dark matter with narrow-gap semiconductors

Authors: P. Abbamonte, A. Albert, D. S. M. Alves, J. Anczarski, T. Aralis, T. U. Böhm, C. Boyd, J. Chen, P. -H. Chu, M. S. Cook, C. W. Fink, M. L. Graesser, Y. Kahn, C. S. Kengle, T. Kucinski, N. A. Kurinsky, C. Lane, A. Leder, R. Massarczyk, A. Mazumdar, S. J. Meijer, W. Nie, E. A. Peterson, A. Phipps, F. Ronning , et al. (9 additional authors not shown)

Abstract: We present the design and current status of SPLENDOR, a novel detector platform that combines narrow-gap semiconductor targets with low-noise charge readout to achieve sensitivity to dark matter energy deposits well below the eV scale. SPLENDOR is designed to be a modular and scalable system able to accommodate different target materials and signal readout technologies. SPLENDOR's present strategy… ▽ More We present the design and current status of SPLENDOR, a novel detector platform that combines narrow-gap semiconductor targets with low-noise charge readout to achieve sensitivity to dark matter energy deposits well below the eV scale. SPLENDOR is designed to be a modular and scalable system able to accommodate different target materials and signal readout technologies. SPLENDOR's present strategy entails: (i) the use of strongly correlated f-electron semiconductors with anisotropic electronic structures to enable not only sub-eV energy thresholds, but also directional sensitivity to the incoming dark matter flux, allowing for signal-background discrimination via daily modulation, and (ii) custom charge readout based on cryogenic high-electron-mobility transistor (cryoHEMT) amplifiers approaching single-electron resolution. We report on the selection and characterization of Eu$_5$In$_2$Sb$_6$ as the target material for SPLENDOR's first prototype detector, as well as the development and calibration of the prototype amplifier chain, achieving a measured charge resolution of 20$\pm$7 electrons in silicon test samples, consistent with predicted performance. This provides a demonstration of the detector architecture, which is now ready for deployment in a dark matter search campaign to deliver SPLENDOR's first science results. Finally, we present estimates of sensitivity reach in the parameter space of athermally produced relic dark matter under high- and low-background environments, and for various amplifier technology upgrades with increasing performance, including planned quantum sensing upgrades in order to achieve our ultimate goal of sub-electron resolution in optimized systems. SPLENDOR provides a novel approach to dark matter direct detection, combining quantum sensing with material's design to open new avenues of exploration in the sub-MeV mass range of dark matter parameter space. △ Less

Submitted 15 August, 2025; v1 submitted 23 July, 2025; originally announced July 2025.

Comments: New figure/discussion added comparing optical conductivity data with DFT calculations for Eu5In2Sb6. Fig. 19 replaced with log-log scale version. Relation between activation energy and bandgap corrected, which resulted in small adjustments of several figures, including reach projections. Some parameters in Table I modified. Parameter space of dark-sink models added to Sec. IV. References added

Report number: LA-UR-25-26113

Impact of Electron Transport Models on Capillary Discharge Plasmas

Authors: A. Diaw, S. J. Coleman, N. M. Cook, J. Edelen, E. C. Hansen, P. Tzeferacos

Abstract: Magnetohydrodynamics (MHD) can be used to model capillary discharge waveguides in laser-wakefield accelerators. However, the predictive capability of MHD can suffer due to poor microscopic closure models. Here, we study the impact of electron heating and thermal conduction on capillary waveguide performance as part of an effort to understand and quantify uncertainties in modeling and designing nex… ▽ More Magnetohydrodynamics (MHD) can be used to model capillary discharge waveguides in laser-wakefield accelerators. However, the predictive capability of MHD can suffer due to poor microscopic closure models. Here, we study the impact of electron heating and thermal conduction on capillary waveguide performance as part of an effort to understand and quantify uncertainties in modeling and designing next-generation plasma accelerators. To do so, we perform two-dimensional high-resolution MHD simulations using an argon-filled capillary discharge waveguide with three different electron transport coefficients models. The models tested include (i) Davies et al. (ii) Spitzer, and (iii) Epperlein-Haines (EH). We found that the EH model overestimates the electron temperature inside the channel by over $20\%$ while predicting a lower azimuthal magnetic field. Moreover, the Spitzer model, often used in MHD simulations for plasma-based accelerators, predicts a significantly higher electron temperature than the other models suggest. △ Less

Submitted 17 March, 2022; originally announced March 2022.

Comments: 9 pages, 5 figures

Linear colliders based on laser-plasma accelerators

Authors: C. Benedetti, S. S. Bulanov, E. Esarey, C. G. R. Geddes, A. J. Gonsalves, A. Huebl, R. Lehe, K. Nakamura, C. B. Schroeder, D. Terzani, J. van Tilborg, M. Turner, J. -L. Vay, T. Zhou, F. Albert, J. Bromage, E. M. Campbell, D. H. Froula, J. P. Palastro, J. Zuegel, D. Bruhwiler, N. M. Cook, B. Cros, M. C. Downer, M. Fuchs , et al. (18 additional authors not shown)

Abstract: White paper to the Proceedings of the U.S. Particle Physics Community Planning Exercise (Snowmass 2021): Linear colliders based on laser-plasma accelerators White paper to the Proceedings of the U.S. Particle Physics Community Planning Exercise (Snowmass 2021): Linear colliders based on laser-plasma accelerators △ Less

Submitted 4 July, 2022; v1 submitted 15 March, 2022; originally announced March 2022.

Comments: Contribution to Snowmass 2021, Accelerator Frontier

Snowmass21 Accelerator Modeling Community White Paper

Authors: S. Biedron, L. Brouwer, D. L. Bruhwiler, N. M. Cook, A. L. Edelen, D. Filippetto, C. -K. Huang, A. Huebl, T. Katsouleas, N. Kuklev, R. Lehe, S. Lund, C. Messe, W. Mori, C. -K. Ng, D. Perez, P. Piot, J. Qiang, R. Roussel, D. Sagan, A. Sahai, A. Scheinker, M. Thévenet, F. Tsung, J. -L. Vay , et al. (2 additional authors not shown)

Abstract: After a summary of relevant comments and recommendations from various reports over the last ten years, this paper examines the modeling needs in accelerator physics, from the modeling of single beams and individual accelerator elements, to the realization of virtual twins that replicate all the complexity to model a particle accelerator complex as accurately as possible. We then discuss cutting-ed… ▽ More After a summary of relevant comments and recommendations from various reports over the last ten years, this paper examines the modeling needs in accelerator physics, from the modeling of single beams and individual accelerator elements, to the realization of virtual twins that replicate all the complexity to model a particle accelerator complex as accurately as possible. We then discuss cutting-edge and emerging computing opportunities, such as advanced algorithms, AI/ML and quantum computing, computational needs in hardware, software performance, portability and scalability, and needs for scalable I/O and in-situ analysis. Considerations of reliability, long-term sustainability, user support and training are considered next, before discussing the benefits of ecosystems with integrated workflows based on standardized input and output, and with integrated frameworks and data repositories developed as a community. Last, we highlight how the community can work more collaboratively and efficiently through the development of consortia and centers, and via collaboration with industry. △ Less

Submitted 22 September, 2022; v1 submitted 15 March, 2022; originally announced March 2022.

Comments: contribution to Snowmass 2021

Anomaly Detection in Particle Accelerators using Autoencoders

Authors: Jonathan P. Edelen, Nathan M. Cook

Abstract: The application of machine learning techniques for anomaly detection in particle accelerators has gained popularity in recent years. These efforts have ranged from the analysis of quenches in radio frequency cavities and superconducting magnets to anomalous beam position monitors, and even losses in rings. Using machine learning for anomaly detection can be challenging owing to the inherent imbala… ▽ More The application of machine learning techniques for anomaly detection in particle accelerators has gained popularity in recent years. These efforts have ranged from the analysis of quenches in radio frequency cavities and superconducting magnets to anomalous beam position monitors, and even losses in rings. Using machine learning for anomaly detection can be challenging owing to the inherent imbalance in the amount of data collected during normal operations as compared to during faults. Additionally, the data are not always labeled and therefore supervised learning is not possible. Autoencoders, neural networks that form a compressed representation and reconstruction of the input data, are a useful tool for such situations. Here we explore the use of autoencoder reconstruction analysis for the prediction of magnet faults in the Advanced Photon Source (APS) storage ring at Argonne National Laboratory. △ Less

Submitted 14 December, 2021; originally announced December 2021.

Journal ref: in Hu, W., Del Vento, D., & Su, S. (Eds.). (2021). Proceedings of the 2021 Improving Scientific Software Conference (No. NCAR/TN-567+PROC)

Modeling of Advanced Accelerator Concepts

Authors: J. -L. Vay, A. Huebl, R. Lehe, N. M. Cook, R. J. England, U. Niedermayer, P. Piot, F. Tsung, D. Winklehner

Abstract: Computer modeling is essential to research on Advanced Accelerator Concepts (AAC), as well as to their design and operation. This paper summarizes the current status and future needs of AAC systems and reports on several key aspects of (i) high-performance computing (including performance, portability, scalability, advanced algorithms, scalable I/Os and In-Situ analysis), (ii) the benefits of ecos… ▽ More Computer modeling is essential to research on Advanced Accelerator Concepts (AAC), as well as to their design and operation. This paper summarizes the current status and future needs of AAC systems and reports on several key aspects of (i) high-performance computing (including performance, portability, scalability, advanced algorithms, scalable I/Os and In-Situ analysis), (ii) the benefits of ecosystems with integrated workflows based on standardized input and output and with integrated frameworks developed as a community, and (iii) sustainability and reliability (including code robustness and usability). △ Less

Submitted 14 September, 2021; v1 submitted 10 September, 2021; originally announced September 2021.

Simulations of Future Particle Accelerators: Issues and Mitigations

Authors: D. Sagan, M. Berz, N. M. Cook, Y. Hao, G. Hoffstaetter, A. Huebl, C. -K. Huang, M. H. Langston, C. E. Mayes, C. E. Mitchell, C. -K. Ng, J. Qiang, R. D. Ryne, A. Scheinker, E. Stern, J. -L. Vay, D. Winklehner, H. Zhang

Abstract: The ever increasing demands placed upon machine performance have resulted in the need for more comprehensive particle accelerator modeling. Computer simulations are key to the success of particle accelerators. Many aspects of particle accelerators rely on computer modeling at some point, sometimes requiring complex simulation tools and massively parallel supercomputing. Examples include the modeli… ▽ More The ever increasing demands placed upon machine performance have resulted in the need for more comprehensive particle accelerator modeling. Computer simulations are key to the success of particle accelerators. Many aspects of particle accelerators rely on computer modeling at some point, sometimes requiring complex simulation tools and massively parallel supercomputing. Examples include the modeling of beams at extreme intensities and densities (toward the quantum degeneracy limit), and with ultra-fine control (down to the level of individual particles). In the future, adaptively tuned models might also be relied upon to provide beam measurements beyond the resolution of existing diagnostics. Much time and effort has been put into creating accelerator software tools, some of which are highly successful. However, there are also shortcomings such as the general inability of existing software to be easily modified to meet changing simulation needs. In this paper possible mitigating strategies are discussed for issues faced by the accelerator community as it endeavors to produce better and more comprehensive modeling tools. This includes lack of coordination between code developers, lack of standards to make codes portable and/or reusable, lack of documentation, among others. △ Less

Submitted 24 August, 2021; originally announced August 2021.

Comments: 21 pages, 1 figure. To be published in JINST

Fabrication of superconducting through-silicon vias

Authors: Justin L. Mallek, Donna-Ruth W. Yost, Danna Rosenberg, Jonilyn L. Yoder, Gregory Calusine, Matt Cook, Rabindra Das, Alexandra Day, Evan Golden, David K. Kim, Jeffery Knecht, Bethany M. Niedzielski, Mollie Schwartz, Arjan Sevi, Corey Stull, Wayne Woods, Andrew J. Kerman, William D. Oliver

Abstract: Increasing circuit complexity within quantum systems based on superconducting qubits necessitates high connectivity while retaining qubit coherence. Classical micro-electronic systems have addressed interconnect density challenges by using 3D integration with interposers containing through-silicon vias (TSVs), but extending these integration techniques to superconducting quantum systems is challen… ▽ More Increasing circuit complexity within quantum systems based on superconducting qubits necessitates high connectivity while retaining qubit coherence. Classical micro-electronic systems have addressed interconnect density challenges by using 3D integration with interposers containing through-silicon vias (TSVs), but extending these integration techniques to superconducting quantum systems is challenging. Here, we discuss our approach for realizing high-aspect-ratio superconducting TSVs\textemdash 10 $μ$m wide by 20 $μ$m long by 200 $μ$m deep\textemdash with densities of 100 electrically isolated TSVs per square millimeter. We characterize the DC and microwave performance of superconducting TSVs at cryogenic temperatures and demonstrate superconducting critical currents greater than 20 mA. These high-aspect-ratio, high critical current superconducting TSVs will enable high-density vertical signal routing within superconducting quantum processors. △ Less

Submitted 15 March, 2021; originally announced March 2021.

Comments: 14 pages, 7 figures

Solid-state qubits integrated with superconducting through-silicon vias

Authors: Donna-Ruth W. Yost, Mollie E. Schwartz, Justin Mallek, Danna Rosenberg, Corey Stull, Jonilyn L. Yoder, Greg Calusine, Matt Cook, Rabindra Das, Alexandra L. Day, Evan B. Golden, David K. Kim, Alexander Melville, Bethany M. Niedzielski, Wayne Woods, Andrew J. Kerman, Willam D. Oliver

Abstract: As superconducting qubit circuits become more complex, addressing a large array of qubits becomes a challenging engineering problem. Dense arrays of qubits benefit from, and may require, access via the third dimension to alleviate interconnect crowding. Through-silicon vias (TSVs) represent a promising approach to three-dimensional (3D) integration in superconducting qubit arrays -- provided they… ▽ More As superconducting qubit circuits become more complex, addressing a large array of qubits becomes a challenging engineering problem. Dense arrays of qubits benefit from, and may require, access via the third dimension to alleviate interconnect crowding. Through-silicon vias (TSVs) represent a promising approach to three-dimensional (3D) integration in superconducting qubit arrays -- provided they are compact enough to support densely-packed qubit systems without compromising qubit performance or low-loss signal and control routing. In this work, we demonstrate the integration of superconducting, high-aspect ratio TSVs -- 10 $μ$m wide by 20 $μ$m long by 200 $μ$m deep -- with superconducting qubits. We utilize TSVs for baseband control and high-fidelity microwave readout of qubits using a two-chip, bump-bonded architecture. We also validate the fabrication of qubits directly upon the surface of a TSV-integrated chip. These key 3D integration milestones pave the way for the control and readout of high-density superconducting qubit arrays using superconducting TSVs. △ Less

Submitted 29 September, 2020; v1 submitted 23 December, 2019; originally announced December 2019.

Comments: 8 pages; 4 figures

Journal ref: npj Quantum Information 6, 59 (2020)

Optimised information gathering in smartphone users

Authors: Arko Ghosh, Jean-Pascal Pfister, Matthew Cook

Abstract: Human activities from hunting to emailing are performed in a fractal-like scale invariant pattern. These patterns are considered efficient for hunting or foraging, but are they efficient for gathering information? Here we link the scale invariant pattern of inter-touch intervals on the smartphone to optimal strategies for information gathering. We recorded touchscreen touches in 65 individuals for… ▽ More Human activities from hunting to emailing are performed in a fractal-like scale invariant pattern. These patterns are considered efficient for hunting or foraging, but are they efficient for gathering information? Here we link the scale invariant pattern of inter-touch intervals on the smartphone to optimal strategies for information gathering. We recorded touchscreen touches in 65 individuals for a month and categorized the activity into checking for information vs. sharing content. For both categories, the inter-touch intervals were well described by power-law fits spanning 5 orders of magnitude, from 1 s to several hours. The power-law exponent typically found for checking was 1.5 and for generating it was 1.3. Next, by using computer simulations we addressed whether the checking pattern was efficient - in terms of minimizing futile attempts yielding no new information. We find that the best performing power law exponent depends on the duration of the assessment and the exponent of 1.5 was the most efficient in the short-term i.e. in the few minutes range. Finally, we addressed whether how people generated and shared content was in tune with the checking pattern. We assumed that the unchecked posts must be minimized for maximal efficiency and according to our analysis the most efficient temporal pattern to share content was the exponent of 1.3 - which was also the pattern displayed by the smartphone users. The behavioral organization for content generation is different from content consumption across time scales. We propose that this difference is a signature of optimal behavior and the short-term assessments used in modern human actions. △ Less

Submitted 10 January, 2017; originally announced January 2017.

Comments: 14 pages, 2 figures

Symplectic Modeling of Beam Loading in Electromagnetic Cavities

Authors: Dan T. Abell, Nathan M. Cook, Stephen D. Webb

Abstract: Simulating beam loading in radiofrequency accelerating structures is critical for understanding higher-order mode effects on beam dynamics, such as beam break-up instability in energy recovery linacs. Full wave simulations of beam loading in radiofrequency structures are computationally expensive, while reduced models can ignore essential physics and can be difficult to generalize. We present a se… ▽ More Simulating beam loading in radiofrequency accelerating structures is critical for understanding higher-order mode effects on beam dynamics, such as beam break-up instability in energy recovery linacs. Full wave simulations of beam loading in radiofrequency structures are computationally expensive, while reduced models can ignore essential physics and can be difficult to generalize. We present a self-consistent algorithm derived from the least-action principle which can model an arbitrary number of cavity eigenmodes and with a generic beam distribution. △ Less

Submitted 10 March, 2017; v1 submitted 1 November, 2016; originally announced November 2016.

Comments: 10 pages, 6 figures

Journal ref: Phys. Rev. Accel. Beams 20, 052002 (2017)

A Spectral Symplectic Algorithm for Cylindrical Electromagnetic Plasma Simulations

Authors: Stephen D. Webb, Dan T. Abell, Nathan M. Cook, David L. Bruhwiler

Abstract: Symplectic integrators for Hamiltonian systems have been quite successful for studying few-body dynamical systems. These integrators are frequently derived using a formalism built on symplectic maps. There have been recent efforts to extend the symplectic approach to plasmas, which have focused primarily on discrete Lagrangian mechanics. In this paper, we derive a a symplectic electromagnetic macr… ▽ More Symplectic integrators for Hamiltonian systems have been quite successful for studying few-body dynamical systems. These integrators are frequently derived using a formalism built on symplectic maps. There have been recent efforts to extend the symplectic approach to plasmas, which have focused primarily on discrete Lagrangian mechanics. In this paper, we derive a a symplectic electromagnetic macroparticle algorithm using the map formalism. The resulting algorithm is designed to prevent numerical instabilities such as numerical Čerenkov, which result from incorrect dispersion relations for the fields, as well as the artificial heating of plasmas, which arise from the non-symplectic nature of conventional particle-in-cell algorithms. This is the first self-consistent electromagnetic algorithm derived using a map-based approach. △ Less

Submitted 9 May, 2017; v1 submitted 16 September, 2016; originally announced September 2016.

Comments: 22 pages -- Text contains an error in the basis functions, and requires some work to fix. An updated version will be posted when this is done

A homotopic mapping between current-based and conductance-based synapses in a mesoscopic neural model of epilepsy

Authors: Andre D. H. Peterson, Hamish Meffin, Mark J. Cook, David B. Grayden, Iven M. Y Mareels, Anthony N. Burkitt

Abstract: Changes in brain states, as found in many neurological diseases such as epilepsy, are often described as bifurcations in mesoscopic neural models. Nearly all of these models rely on a mathematically convenient, but biophysically inaccurate, description of the synaptic input to neurons called current-based synapses. We develop a novel analytical framework to analyze the effects of a more biophysica… ▽ More Changes in brain states, as found in many neurological diseases such as epilepsy, are often described as bifurcations in mesoscopic neural models. Nearly all of these models rely on a mathematically convenient, but biophysically inaccurate, description of the synaptic input to neurons called current-based synapses. We develop a novel analytical framework to analyze the effects of a more biophysically realistic description, known as conductance-based synapses. These are implemented in a mesoscopic neural model and compared to the standard approximation via a single parameter homotopic mapping. A bifurcation analysis using the homotopy parameter demonstrates that if a more realistic synaptic coupling mechanism is used in this class of models, then a bifurcation or transition to an abnormal brain state does not occur in the same parameter space. We show that the more realistic coupling has additional mathematical parameters that require a fundamentally different biophysical mechanism to undergo a state transition. These results demonstrate the importance of incorporating more realistic synapses in mesoscopic neural models and challenge the accuracy of previous models, especially those describing brain state transitions such as epilepsy. △ Less

Submitted 15 December, 2018; v1 submitted 1 October, 2015; originally announced October 2015.

Comments: This is the submitted version

Design principles for shift current photovoltaics

Authors: Ashley M. Cook, Benjamin M. Fregoso, Fernando de Juan, Sinisa Coh, Joel E. Moore

Abstract: While the basic principles and limitations of conventional solar cells are well understood, relatively little attention has gone toward maximizing the potential efficiency of photovoltaic devices based on shift currents. In this work, we outline simple design principles for the optimization of shift currents for frequencies near the band gap, derived from the analysis of a general effective model.… ▽ More While the basic principles and limitations of conventional solar cells are well understood, relatively little attention has gone toward maximizing the potential efficiency of photovoltaic devices based on shift currents. In this work, we outline simple design principles for the optimization of shift currents for frequencies near the band gap, derived from the analysis of a general effective model. The use of a novel sum rule allows us to express the band edge shift current in terms of a few model parameters and to show it depends explicitly on wavefunctions via Berry connections in addition to standard band structure. We use our approach to identify two new classes of shift current photovoltaics, ferroelectric polymer films and single-layer orthorhombic monochalcogenides such as GeS. We introduce tight-binding models for these systems, and show that they exhibit the largest shift current responsivities at the band edge reported so far. Moreover, exploring the parameter space of these models we find photoresponsivities that can exceed $100$ mA/W. Our results show how the study of the shift current via effective models allows one to improve the possible efficiency of devices based on this mechanism and better grasp their potential to compete with conventional solar cells. △ Less

Submitted 20 January, 2017; v1 submitted 30 July, 2015; originally announced July 2015.

Comments: 10 pages, 4 figures, AC and BMF share equal contributions. Published in Nature Communications

The effect of thermophoresis on the discharge parameters in complex plasma experiments

Authors: Victor Land, Jorge Carmona-Reyes, James Creel, Jimmy Schmoke, Mike Cook, Lorin Matthews, Truell Hyde

Abstract: Thermophoresis is a tool often applied in complex plasma experiments. One of the usual stated benefits over other experimental tools is that changes induced by thermophoresis neither directly depend on, nor directly influence, the plasma parameters. From electronic data, plasma emission profiles in the sheath, and Langmuir probe data in the plasma bulk, we conclude that this assumption does not ho… ▽ More Thermophoresis is a tool often applied in complex plasma experiments. One of the usual stated benefits over other experimental tools is that changes induced by thermophoresis neither directly depend on, nor directly influence, the plasma parameters. From electronic data, plasma emission profiles in the sheath, and Langmuir probe data in the plasma bulk, we conclude that this assumption does not hold. An important effect on the levitation of dust particles in argon plasma is observed as well. The reason behind the changes in plasma parameters seems to be the change in neutral atom density accompanying the increased gas temperature while running at constant pressure. △ Less

Submitted 20 October, 2010; originally announced October 2010.

Comments: 14 pages, 12 figures

Report number: CASPER-10-06

Low-Velocity Impacts on PVDF Targets Using a Light Gas Gun

Authors: J. A. Carmona, M. Cook, J. Schmoke, R. Laufer, L. S. Matthews, T. Hyde

Abstract: Orbital debris is a constraint on the long-term health of any spacecraft and must be consi-dered during mission planning. Varying mechanisms have been proposed to quantify the problem. Accurate in-situ data is essential with various types of sensors designed to detect orbital debris impacts employed on space missions since the 1950's [1]. The earliest of these was the PZT (piezoelectric lead zirco… ▽ More Orbital debris is a constraint on the long-term health of any spacecraft and must be consi-dered during mission planning. Varying mechanisms have been proposed to quantify the problem. Accurate in-situ data is essential with various types of sensors designed to detect orbital debris impacts employed on space missions since the 1950's [1]. The earliest of these was the PZT (piezoelectric lead zirconate tita-nate) sensor which was often used in-situ to measure the momentum of a particle at the time of impact. More recently, PVDF (Polyvinylidene fluoride) [2] has been employed as it exhibits piezoelectric capabilities along with the advantages of ruggedness, no bias re-quirement, ease of large area sensor construction, high counting rate capability, and space reliability, making it an ideal space debris sensor. Its large sensing sur-face area and ease of integration into a PZT sensor system makes it a desirable element in any in-situ space debris sensor. △ Less

Submitted 19 October, 2010; originally announced October 2010.

Report number: CASPER-10-09

A low-voltage retarding-field Mott polarimeter for photocathode characterization

Authors: James L. McCarter, Marcy L. Stutzman, Kenneth W. Trantham, Tyler G. Anderson, April M. Cook, Timothy J. Gay

Abstract: Nuclear physics experiments at Thomas Jefferson National Accelerator Facility's CEBAF rely on high polarization electron beams. We describe a recently commissioned system for prequalifying and studying photocathodes for CEBAF with a load-locked, low-voltage polarized electron source coupled to a compact retarding-field Mott polarimeter. The polarimeter uses simplified electrode structures and o… ▽ More Nuclear physics experiments at Thomas Jefferson National Accelerator Facility's CEBAF rely on high polarization electron beams. We describe a recently commissioned system for prequalifying and studying photocathodes for CEBAF with a load-locked, low-voltage polarized electron source coupled to a compact retarding-field Mott polarimeter. The polarimeter uses simplified electrode structures and operates from 5 to 30 kV. The effective Sherman function for this device has been calibrated by comparison with the CEBAF 5 MeV Mott polarimeter. For elastic scattering from a thick gold target at 20 keV, the effective Sherman function is 0.201(5). Its maximum efficiency at 20 keV, defined as the detected count rate divided by the incident particle current, is 5.4(2) x 10-4, yielding a figure-of-merit, or analyzing power squared times efficiency, of 1.0(1) x 10-5. The operating parameters of this new polarimeter design are compared to previously published data for other compact Mott polarimeters of the retarding-field type. △ Less

Submitted 29 March, 2010; originally announced March 2010.

Comments: 9 figures

Journal ref: Nucl.Instrum.Meth.A618:30-36,2010

Investigation of Dust Wake Field Oscillations

Authors: J. Kong, T. Hyde, L. Matthews, M. Cook, J. Schmoke, J. Carmona-Reyes

Abstract: Wakefield oscillations created by the ion wakefield existing below a dust particle within the plasma sheath generated above a powered lower electrode in a GEC rf reference cell carry information about the plasma sheath, the dust particle charge and the speed of the streaming ions. An experimental method to investigate such wakefield oscillations is discussed. Wakefield oscillations created by the ion wakefield existing below a dust particle within the plasma sheath generated above a powered lower electrode in a GEC rf reference cell carry information about the plasma sheath, the dust particle charge and the speed of the streaming ions. An experimental method to investigate such wakefield oscillations is discussed. △ Less

Submitted 24 July, 2007; originally announced July 2007.

Report number: CASPER-07-06

Low-Velocity Impacts on Targets Containing Embedded Carbon Nanotubes

Authors: J. A. Carmona, M. Cook, J. Schmoke, J. Reay, T. W. Hyde

Abstract: A one stage Light Gas Gun (LGG) at CASPER [1] was employed to test the shielding capabilities of tiles composed of four different laminated nanotube combinations. These target tiles were named CSNEAT1, CSCNT1, HYCNTUT1 and HYCNTT1. For calibration purposes, a 3003- aluminum plate was also impacted and the craters formed on the various composition tiles compared. A one stage Light Gas Gun (LGG) at CASPER [1] was employed to test the shielding capabilities of tiles composed of four different laminated nanotube combinations. These target tiles were named CSNEAT1, CSCNT1, HYCNTUT1 and HYCNTT1. For calibration purposes, a 3003- aluminum plate was also impacted and the craters formed on the various composition tiles compared. △ Less

Submitted 29 March, 2006; originally announced March 2006.

Report number: CASPER-06-01

Construction of a PZT Sensor Network for Low and Hypervelocity Impact Detection

Authors: J. A. Carmona, M. Cook, M. Cooper, J. Schmoke, J. Reay, L. Matthews, T. Hyde

Abstract: Orbital debris is a constraint on the long-term health of any spacecraft and must be considered during mission planning. Varying mechanisms have been proposed to quantify the problem. Assessment of orbital debris employing ground-based methods such as radar can help determine where debris clouds are located as well as their density or orbital trajectory. Such data is invaluable to computer simul… ▽ More Orbital debris is a constraint on the long-term health of any spacecraft and must be considered during mission planning. Varying mechanisms have been proposed to quantify the problem. Assessment of orbital debris employing ground-based methods such as radar can help determine where debris clouds are located as well as their density or orbital trajectory. Such data is invaluable to computer simulations and can allow predictions of the debris environment over specific time periods [1]. Accurate in-situ data is essential as well with various types of sensors designed to detect orbital debris impacts employed on space missions since the 1950's [2]. One of the most common of these is the PZT (piezoelectric lead zirconate titanate) which is often used in-situ to measure the momentum of a particle at the time of impact. This paper will discuss a multiple PZT sensor system capable of determining both impactor momentum and location currently in development within CASPER. △ Less

Submitted 10 January, 2005; originally announced January 2005.

Comments: 2 pages

Report number: CASPER-05-01

Impact Studies Using a One Stage Light Gas Gun

Authors: Jorge Carmona, Mike Cook, Jimmy Schmoke, Katie Harper, Jerry Reay, Lorin Matthews, Truell Hyde

Abstract: The Center for Astrophysics,Space Physics, and Engineering Research (CASPER) has completed construction and calibration of a Light Gas Gun (LGG), which is used for low velocity impact studies. At geosynchronous orbit, space debris can impact commercial satellites at velocities of 500 m/s [1] reducing their useful lifetime. Additionally, there is an ever-increasing population of abandoned nonoper… ▽ More The Center for Astrophysics,Space Physics, and Engineering Research (CASPER) has completed construction and calibration of a Light Gas Gun (LGG), which is used for low velocity impact studies. At geosynchronous orbit, space debris can impact commercial satellites at velocities of 500 m/s [1] reducing their useful lifetime. Additionally, there is an ever-increasing population of abandoned nonoperational satellites and related debris in these orbits [2]. Therefore, it is important to clearly understand the physics behind how such collisions can cause structural damage. This is most easily determined by measuring the damage incurred on representative material exposed to test collisions in the laboratory. Data collected in this manner will not only help illuminate the shock physics involved but can also aid in providing methods for designing advanced shielding for satellites. △ Less

Submitted 29 January, 2004; originally announced January 2004.

Comments: 2 pages, Lunar and Planetary Science XXXV

Report number: CASPER-04-02

Dusty Plasma Correlation Function Experiment

Authors: B. Smith, J. Vasut, T. Hyde, L. Matthews, J. Reay, M. Cook, J. Schmoke

Abstract: Dust particles immersed within a plasma environment, such as those in protostellar clouds, planetary rings or cometary environments, will acquire an electric charge. If the ratio of the inter-particle potential energy to the average kinetic energy is high enough the particles will form either a "liquid" structure with short-range ordering or a crystalline structure with long range ordering. Many… ▽ More Dust particles immersed within a plasma environment, such as those in protostellar clouds, planetary rings or cometary environments, will acquire an electric charge. If the ratio of the inter-particle potential energy to the average kinetic energy is high enough the particles will form either a "liquid" structure with short-range ordering or a crystalline structure with long range ordering. Many experiments have been conducted over the past several years on such colloidal plasmas to discover the nature of the crystals formed, but more work is needed to fully understand these complex colloidal systems. Most previous experiments have employed monodisperse spheres to form Coulomb crystals. However, in nature (as well as in most plasma processing environments) the distribution of particle sizes is more randomized and disperse. This paper reports experiments which were carried out in a GEC rf reference cell modified for use as a dusty plasma system, using varying sizes of particles to determine the manner in which the correlation function depends upon the overall dust grain size distribution. (The correlation function determines the overall crystalline structure of the lattice.) Two dimensional plasma crystals were formed of assorted glass spheres with specific size distributions in an argon plasma. Using various optical techniques, the pair correlation function was determined and compared to those calculated numerically. △ Less

Submitted 18 August, 2003; originally announced August 2003.

Comments: 6 pages, Presented at COSPAR '03

Report number: CASPER-03-07