arXiv subjects

Chris Orban

Publications and source records attributed to Chris Orban.

At least 19 recordsLinked to original sources

arXiv2025

Applying Machine Learning Methods to Laser Acceleration of Protons: Synthetic Data for Exploring the High Repetition Rate Regime

Advances in ultra-intense laser technology have increased repetition rates and average power for chirped-pulse laser systems, which offers a promising solution for many applications including energetic proton sources. An important challenge is the need to optimize and control the proton source by varying some of the many degrees of freedom inherent to the laser-plasma interactions. Machine learning can play an important role in this task, as our work examines. Building on our earlier work in Desai et al. 2024, we generate a large $\sim$1.5 million data point synthetic data set for proton acceleration using a physics-informed analytic model that we improved to include pre-pulse physics. Then, we train different machine learning methods on this data set to determine which methods perform efficiently and accurately. Generally, we find that quasi-real-time training of neural network models using single shot data from a kHz repetition rate ultra-intense laser system should typically be feasible on a single GPU. We also find that a less sophisticated model like a polynomial regression can be trained even faster and that the accuracy of these models is still good enough to be useful. We provide our source code and example synthetic data for others to test new machine learning methods and approaches to automated learning in this regime.

physics.plasm-ph↗

arXiv2025

Towards Intelligent Control of MeV Electrons and Protons from kHz Repetition Rate Ultra-Intense Laser Interactions

Ultra-intense laser-matter interactions are often difficult to predict from first principles because of the complexity of plasma processes and the many degrees of freedom relating to the laser and target parameters. An important approach to controlling and optimizing ultra-intense laser interactions involves gathering large data sets and using this data to train statistical and machine learning models. In this paper we describe experimental efforts to accelerate electrons and protons to $\sim$MeV energies with this goal in mind. These experiments involve a 1 kHz repetition rate ultra-intense laser system with $\sim$10mJ per shot, a peak intensity near $5 \times 10^{18}$ W/cm$^{2}$, and a "liquid leaf" target. Improvements to the data acquisition capabilities of this laser system greatly aided this investigation. Generally, we find that the trained models were very effective for controlling the numbers of MeV electrons ejected. The models were less successful at shifting the energy range of ejected electrons. Simultaneous control of the numbers of $\sim$MeV electrons and the energy range will be the subject of future experimentation using this platform.

physics.plasm-ph↗

arXiv2024

Applying Machine Learning Methods to Laser Acceleration of Protons: Lessons Learned from Synthetic Data

Researchers in the field of ultra-intense laser science are beginning to embrace machine learning methods. In this study we consider three different machine learning methods -- a two-hidden layer neural network, Support Vector Regression and Gaussian Process Regression -- and compare how well they can learn from a synthetic data set for proton acceleration in the Target Normal Sheath Acceleration regime. The synthetic data set was generated from a previously published theoretical model by Fuchs et al. 2005 that we modified. Once trained, these machine learning methods can assist with efforts to maximize the peak proton energy, or with the more general problem of configuring the laser system to produce a proton energy spectrum with desired characteristics. In our study we focus on both the accuracy of the machine learning methods and the performance on one GPU including the memory consumption. Although it is arguably the least sophisticated machine learning model we considered, Support Vector Regression performed very well in our tests.

physics.plasm-ph↗

arXiv2023

Particle-In-Cell Code Comparison for Ion Acceleration: EPOCH and Smilei

Particle-in-Cell (PIC) codes are a popular tool to model laser-plasma interactions. Many different PIC codes already exist, and many new PIC codes are being developed constantly. It is therefore important to compare different PIC codes to ascertain which code is best suited for a particular kind of physical problem. In a paper by Smith et al. (2021) they compared three different codes on a problem relating to proton acceleration in the Target Normal Sheath Acceleration regime from a normal incidence ultra-intense laser pulse. Smith et al. (2021) included in their study the widely used EPOCH code. However, they did not include results from the Smilei code, which is another popular PIC code in the plasma community with a variety of features and physics packages. In the present work, we compare the Smilei code to the EPOCH code for the same test case as Smith et al. (2021). Broadly we find the two codes to be highly consistent with agreement in total ion, electron, and field energy at a percent level or better. The electron and ion energy distribution functions agree well at lower energies and the differences at higher energies (e.g. because of the finite number of macroparticles) are similar to what Smith et al. (2021) saw for other codes. We found that Smilei consumed 25% more RAM than EPOCH did but the execution time was 30% less for Smilei on one processor. We include the input files to encourage future comparisons.

physics.plasm-ph↗

arXiv2022

Methods to Simplify Object Tracking in Video Data

Recent years have seen an explosion of interest in analyzing the motion of objects in video data as a way for students to connect the concepts of physics to something tangible like a video recording of an experiment. A variety of software exists for students to look at individual frames and click on the object to infer the x,y position. Some of these tools include a capability to automatically identify the position of the object in the frame. But it is not unusual, especially when inexperienced users are recording the video and configuring the program, for these algorithms to struggle to "lock on" to the moving object. In this paper, we both include some general advice to help object tracking algorithms locate an object and we provide our own algorithms that are simpler and potentially more effective than the sophisticated image processing algorithms that are currently being used. These algorithms focus not on a "template image" of the moving object but instead distinguish between the object and the background by analyzing only the colors of individual pixels. These algorithms are built into a free and open source program called the STEMcoding Object Tracker (http://go.osu.edu/objecttracker) which works in the browser (without any downloads) and is compatible with a variety of operating systems including chromebooks.

physics.ed-ph↗

arXiv2022

Code-to-Code Comparison and Validation of the Radiation-Hydrodynamics Capabilities of the FLASH Code Using a Laboratory Astrophysical Jet

The potential for laser-produced plasmas to yield fundamental insights into high energy density physics (HEDP) and deliver other useful applications can sometimes be frustrated by uncertainties in modeling the properties and behavior of these plasmas using radiation-hydrodynamics codes. In an effort to overcome this and to corroborate the accuracy of the HEDP capabilities in the publicly available FLASH radiation-hydrodynamics code, we present detailed code-to-code comparisons between FLASH and the HYDRA code developed at Lawrence Livermore National Laboratory using previously published HYDRA simulations from Grava et al. (2008). That study describes a laser experiment that produced a jet-like feature that the authors compare to astrophysical jets. Importantly, the Grava et al. (2008) experiment included detailed x-ray interferometric measurements of electron number densities and a time-integrated measurement of the soft x-ray spectrum. Despite markedly different methods for treating the computational mesh, and different equation of state and opacity models, the FLASH results resemble the results from HYDRA and, most importantly, the experimental measurements of electron density. Having validated the FLASH code in this way, we use the code to further investigate and understand the formation of the jet seen in the Grava et al. (2008) experiment and discuss its relation to the Wan et al. (1997) experiment at the NOVA laser.

physics.plasm-ph↗

arXiv2021

Particle-in-Cell modeling of a potential demonstration experiment for double pulse enhanced target normal sheath acceleration

Ultra intense lasers are a promising source of energetic ions for various applications. An interesting approach described in Ferri et al. 2019 argues from Particle-in-Cell simulations that using two laser pulses of half energy (half intensity) arriving with close to 45 degrees angle of incidence is significantly more effective at accelerating ions than one pulse at full energy (full intensity). For a variety of reasons, at the time of this writing there has not yet been a true experimental confirmation of this enhancement. In this paper we perform 2D Particle-in-Cell simulations to examine if a milliJoule class, 5x10^18 W cm^-2 peak intensity laser system could be used for such a demonstration experiment. Laser systems in this class can operate at a kHz rate which should be helpful for addressing some of the challenges of performing this experiment. Despite investigating a 3.5 times lower intensity than Ferri et al. 2019 did, we find that the double pulse approach enhances the peak proton energy and the energy conversion to protons by a factor of about three compared to a single laser pulse with the same total laser energy. We also comment on the nature of the enhancement and describe simulations that examine how the enhancement may depend on the spatial or temporal alignment of the two pulses.

physics.plasm-ph↗

arXiv2021

A Particle-In-Cell Code Comparison for Ion Acceleration: EPOCH, LSP, and WarpX

There are now more Particle-in-Cell (PIC) codes than ever before that researchers use to simulate intense laser-plasma interactions. To date, there have been relatively few direct comparisons of these codes in the literature, especially for relativistic intensity lasers interacting with thin overdense targets. To address this we perform a code comparison of three PIC codes: EPOCH, LSP, and WarpX for the problem of laser-driven ion acceleration in a 2D(3v) geometry for a $10^{20}$ W cm$^{-2}$ intensity laser. We examine the plasma density, ion energy spectra, and laser-plasma coupling of the three codes and find strong agreement. We also run the same simulation 20 times with different random seeds to explore statistical fluctuations of the outputs. We then compare the execution times and memory usage of the codes (without "tuning" to improve performance) using between 1 and 48 processors on one node. We provide input files to encourage larger and more frequent code comparisons in this field.

physics.plasm-ph↗

arXiv2020

Optimizing Laser-Plasma Interactions for Ion Acceleration using Particle-in-Cell Simulations and Evolutionary Algorithms

The development of ultra-intense laser-based sources of high energy ions is an important goal, with a variety of potential applications. One of the barriers to achieving this goal is the need to maximize the conversion efficiency from laser energy to ion energy. We apply a new approach to this problem, in which we use an evolutionary algorithm to optimize conversion efficiency by exploring variations of the target density profile with thousands of one-dimensional particle-in-cell (PIC) simulations. We then compare this "optimal" target identified by the one-dimensional PIC simulations to more conventional choices, such as with an exponential scale length pre-plasma, with fully three-dimensional PIC simulations. The optimal target outperforms the conventional targets in terms of maximum ion energy by 20% and show a significant enhancement of conversion efficiency to high energy ions. This target geometry enhances laser coupling to the electrons, while still allowing the laser to strongly reflect from an effectively thin target. These results underscore the potential for this statistics-driven approach to guide research into optimizing laser-plasma simulations and experiments.

physics.plasm-ph↗

arXiv2019

Computational Thinking in Introductory Physics

Computational Thinking (CT) is still a relatively new term in the lexicon of learning objectives and science standards. There is not yet widespread agreement on the precise definition or implementation of CT, and efforts to assess CT are still maturing, even as more states adopt K-12 computer science standards. In this article we will try to summarize what CT means for a typical introductory (i.e. high school or early college) physics class. This will include a discussion of the ways that instructors may already be incorporating elements of CT in their classes without knowing it. Our intention in writing this article is to provide a helpful, concise and readable introduction to this topic for physics instructors. We also put forward some ideas for what the future of CT in introductory physics may look like.

physics.ed-ph↗

arXiv2019

Experimental observation and computational modeling of radial Weibel instability in high intensity laser-plasma interactions

When a relativistic intensity laser interacts with the surface of a solid density target, suprathermal electron currents are subject to Weibel instability filamentation when propagating through the thermal population of the bulk target. We present time resolved shadowgraphy of radial ionization front expansion and Weibel instability filamentation within a thin, sub-micron, sheet initiated by irradiation with a short pulse, high intensity laser. High temporal (100 fs) and spatial (1 $μ$m) resolution shadowgraphy of the interaction reveals a relativistic expansion of the ionization front within a 120 $μ$m diameter region surrounding the laser-target interaction, corroborated by simulations to expand at $0.77c$, where $c$ is the speed of light. Filamentation within the patch persists for several picoseconds and seeds the eventual recombination and heating dynamics on the nanosecond timescale. Particle-in-cell simulations were conducted to elucidate the electron dynamics leading to the radial expansion of the critical surface. Computational results report the ionization expansion is due to field ionization of the expanding hot electron population. Filamentation within the expansion is due to the Weibel instability which is supported by the magnetic fields present.

physics.plasm-ph↗

arXiv2019

A controlled study of virtual reality in first-year magnetostatics

Stereoscopic virtual reality (VR) has experienced a resurgence due to flagship products such as the Oculus Rift, HTC Vive and smartphone-based VR solutions like Google Cardboard. This is causing the question to resurface: how can stereoscopic VR be useful in instruction, if at all, and what are the pedagogical best practices for its use? To address this, and to continue our work in this sphere, we performed a study of 289 introductory physics students who were sorted into three different treatment types: stereoscopic virtual reality, WebGL simulation, and static 2D images, each designed to provide information about magnetic fields and forces. Students were assessed using preliminary items designed to focus on heavily-3D systems. We report on assessment reliability, and on student performance. Overall, we find that students who used VR did not significantly outperform students using other treatment types. There were significant differences between sexes, as other studies have noted. Dependence on students' self-reported 3D videogame play was observed, in keeping with previous studies, but this dependence was not restricted to the VR treatment.

physics.ed-ph↗

arXiv2019

Particle-in-Cell Simulations of Density Peak Formation and Ion Acceleration from Short Pulse Laser-Driven Ponderomotive Steepening

We use particle-in-cell (PIC) simulations and simple analytic models to investigate the laser-plasma interaction known as ponderomotive steepening. When normally incident laser light reflects at the critical surface of a plasma, the resulting standing electromagnetic wave modifies the electron density profile via the ponderomotive force, which creates peaks in the electron density separated by approximately half of the laser wavelength. What is less well studied is how this charge imbalance accelerates ions towards the electron density peaks, modifying the ion density profile of the plasma. Idealized PIC simulations with an extended underdense plasma shelf are used to isolate the dynamics of ion density peak growth for a 42 fs pulse from an 800 nm laser with an intensity of 10$^{18}$ W cm$^{-2}$. These simulations exhibit sustained longitudinal electric fields of 200 GV m$^{-1}$, which produce counter-steaming populations of ions reaching a few keV in energy. We compare these simulations to theoretical models, and we explore how ion energy depends on factors such as the plasma density and the laser wavelength, pulse duration, and intensity. We also provide relations for the strength of longitudinal electric fields and an approximate timescale for the density peaks to develop. These conclusions may be useful investigating the phenomenon of ponderomotive steepening as advances in laser technology allow shorter and more intense pulses to be produced at various wavelengths. We also discuss the parallels with other work studying the interference from two counter-propagating laser pulses.

physics.plasm-ph↗

arXiv2018

A Hybrid Approach for Using Programming Exercises in Introductory Physics

Incorporating computer programming exercises into introductory physics is a delicate task that involves a number of choices that may have an effect on student learning. We present a "hybrid" approach that speaks to a number of common concerns regarding cognitive load which arise when using programming exercises in introductory physics classes where many students are absolute beginner programmers. This "hybrid" approach provides the student with a highly interactive web-based visualization, not unlike a PhET or Physlet interactive, but importantly the student is shown only the subset of the code where the initial conditions are set and the system variables are evolved. We highlight results from a coding activity that resembles the classic game Asteroids. The goals of this activity are to show how a simple 1D code can be modified into a 2D code, and to reinforce ideas about the relationship between force, velocity, and acceleration vectors. Survey results from four semesters of introductory physics classes at the Ohio State University's Marion campus, in which a high percentage of the students are weak or absolute beginner programmers, provide evidence that most students can complete coding tasks without severe difficulty. Other survey results are promising for future work where conceptual learning will be assessed in a direct way using metrics like the Animated Force Concept Inventory (Dancy & Beichner 2006). The exercise highlighted here and others from our group are available for general use at http://compadre.org/PICUP

physics.ed-ph↗

arXiv2017

Relativistic electron acceleration by mJ-class kHz lasers normally incident on liquid targets

We report observation of kHz-pulsed-laser-accelerated electron energies up to 3 MeV in the -$k_\text{laser}$ (backward) direction from a 3 mJ laser interacting at normal incidence with a solid density, flowing-liquid target. The electrons/MeV/s.r. >1 MeV recorded here using a mJ-class laser exceeds or equals that of prior super-ponderomotive electron studies employing lasers at lower repetition-rates and oblique incidence. Focal intensity of the 40-fs-duration laser is 1.5 $\cdot$ 10$^{18}$ W cm$^{-2}$, corresponding to only ~80 keV electron ponderomotive energy. Varying laser intensity confirms electron energies in the laser-reflection direction well above what might be expected from ponderomotive scaling in normal-incidence laser-target geometry. This direct, normal-incidence energy spectrum measurement is made possible by modifying the final focusing off-axis-paraboloid (OAP) mirror with a central hole that allows electrons to pass, and restoring laser intensity through adaptive optics. A Lanex-based, optics-free high-acquisition rate (>100 Hz) magnetic electron-spectrometer was developed for this study to enable shot-to-shot statistical analysis and real-time feedback, which was leveraged in finding optimal pre-plasma conditions. 3D Particle-in-cell simulations of the interaction show qualitative super-ponderomotive spectral agreement with experiment. The demonstration of a high-repetition-rate, high-flux source containing >MeV electrons from a few-mJ, 40 fs laser and a simple liquid target encourages development of future $\geq$kHz-repetition, fs-duration electron-beam applications.

physics.plasm-ph↗

arXiv2017

A controlled study of stereoscopic virtual reality in freshman electrostatics

Virtual reality (VR) has long promised to revolutionize education, but with little follow-through. Part of the reason for this is the prohibitive cost of immersive VR headsets or caves. This has changed with the advent of smartphone-based VR (along the lines of Google cardboard) which allows students to use smartphones and inexpensive plastic or cardboard viewers to enjoy stereoscopic VR simulations. We have completed the largest-ever such study on 627 students enrolled in calculus-based freshman physics at The Ohio State University. This initial study focused on student understanding of electric fields. Students were split into three treatments groups: VR, video, and static 2D images. Students were asked questions before, during, and after treatment. Here we present a preliminary analysis including overall post-pre improvement among the treatment groups, dependence of improvement on gender, and previous video game experience. Results on select questions are discussed. Several electric field visualizations similar to those used in this study are freely available on Google Play http://go.osu.edu/BuckeyeVR

physics.ed-ph↗

arXiv2017

A novel approach for using programming exercises in electromagnetism coursework

While there exists a significant number of web interactives for introductory physics, students are almost never shown the computer code that generates these interactives even when the physics parts of these programs are relatively simple. Building off of a set of carefully-designed classical mechanics programming exercises that were constructed with this goal in mind, we present a series of electromagnetism programming exercises in a browser-based framework called p5.js. Importantly, this framework can be used to highlight the physics aspects of an interactive simulation code while obscuring other details. This approach allows absolute beginner programmers to gain experience in modifying and running the program without becoming overwhelmed. We plan to probe the impact on student conceptual learning using the Brief Electricity and Magnetism Assessment and other questions. We invite collaborators and teachers to adopt this framework in their high school or early undergraduate classes. All exercises are available at http://compadre.org/PICUP

physics.ed-ph↗

arXiv2017

A Game-Centered, Interactive Approach for Using Programming Exercises in Introductory Physics

Incorporating computer programming exercises in introductory physics is a delicate task that involves a number of choices that may have a strong affect on student learning. We present an approach that speaks to a number of common concerns that arise when using programming exercises in introductory physics classes where most students are absolute beginner programmers. These students need an approach that is (1) simple, involving 75 or fewer lines of well-commented code, (2) easy to use, with browser-based coding tools, (3) interactive, with a high frame rate to give a video-game like feel, (4) step-by-step with the ability to interact with intermediate stages of the "correct" program and (5) thoughtfully integrated into the physics curriculum, for example, by illustrating velocity and acceleration vectors throughout. We present a set of hour-long activities for classical mechanics that resemble well-known games such as "asteroids", "lunar lander" and "angry birds". Survey results from the first activity from four semesters of introductory physics classes at OSU in which a high percentage of the students are weak or absolute beginner programmers seems to confirm that the level of difficulty is appropriate for this level and that the students enjoy the activity. These exercises are available for general use at http://compadre.org/PICUP In the future we plan to assess conceptual knowledge using an animated version of the Force Concept Inventory originally developed by M. Dancy.

physics.ed-ph↗