arXiv subjects

Scott C. Hsu

Publications and source records attributed to Scott C. Hsu.

At least 19 recordsLinked to original sources

arXiv2025

Continuing progress toward fusion energy breakeven and gain as measured against the Lawson criteria

This paper is an update to our earlier paper ''Progress toward fusion energy breakeven and gain as measured against the Lawson criterion'' [Phys. Plasmas 29, 062103 (2022)]. Plots of Lawson parameter and triple product vs. ion temperature and triple product vs. date achieved are updated with recently published experimental results. A new plot of scientific energy gain vs. date achieved is included. Additionally, notes on new experimental results, clarifications, and a correction are included.

physics.plasm-ph↗

arXiv2022

Progress toward fusion energy breakeven and gain as measured against the Lawson criterion

The Lawson criterion is a key concept in the pursuit of fusion energy, relating the fuel density $n$, pulse duration $τ$ or energy confinement time $τ_E$, and fuel temperature $T$ to the energy gain $Q$ of a fusion plasma. The purpose of this paper is to explain and review the Lawson criterion and to provide a compilation of achieved parameters for a broad range of historical and contemporary fusion experiments. Although this paper focuses on the Lawson criterion, it is only one of many equally important factors in assessing the progress and ultimate likelihood of any fusion concept becoming a commercially viable fusion-energy system. Only experimentally measured or inferred values of $n$, $τ$ or $τ_E$, and $T$ that have been published in the peer-reviewed literature are included in this paper, unless noted otherwise. For extracting these parameters, we discuss methodologies that are necessarily specific to different fusion approaches (including magnetic, inertial, and magneto-inertial fusion). This paper is intended to serve as a reference for fusion researchers and a tutorial for all others interested in fusion energy.

physics.plasm-ph↗

arXiv2021

Potential Early Markets for Fusion Energy

We identify potential early markets for fusion energy and their projected cost targets, based on analysis and synthesis of many relevant, recent studies and reports. Because private fusion companies aspire to start commercial deployment before 2040, we examine cost requirements for fusion-generated electricity, process heat, and hydrogen production based on today's market prices but with various adjustments relating to possible scenarios in 2035, such as "business-as-usual," high renewables penetration, and carbon pricing up to 100 \$/tCO$_2$. Key findings are that fusion developers should consider focusing initially on high-priced global electricity markets and including integrated thermal storage in order to maximize revenue and compete in markets with high renewables penetration. Process heat and hydrogen production will be tough early markets for fusion, but may open up to fusion as markets evolve and if fusion's levelized cost of electricity falls below 50 \$/MWh$_\mathrm{e}$. Finally, we discuss potential ways for a fusion plant to increase revenue via cogeneration (e.g., desalination, direct air capture, or district heating) and to lower capital costs (e.g., by minimizing construction times and interest or by retrofitting coal plants).

physics.soc-ph↗

arXiv2020

Observation of Shock-Front Separation in Multi-Ion-Species Collisional Plasma Shocks

We observe shock-front separation and species-dependent shock widths in multi-ion-species collisional plasma shocks, which are produced by obliquely merging plasma jets of a He/Ar mixture (97% He and 3% Ar by initial number density) on the Plasma Liner Experiment [S. C. Hsu et al., IEEE Trans. Plasma Sci. 46, 1951 (2018)]. Visible plasma emission near the He-I 587.6 nm and Ar-II 476.5-514.5 nm lines are simultaneously recorded by splitting a single visible image of the shock into two different fast-framing cameras with different narrow bandpass filters (589 +/- 5 nm for observing the He-I line and 500 +/- 25 nm for the Ar-II lines). For conditions in these experiments (pre-shock ion and electron densities ~5*10^14 cm^-3, ion and electron temperatures of ~2.2 eV, and relative plasma-merging speed of 22 km/s), the observationally inferred magnitude of He/Ar shock-front separation and the shock widths themselves are < 1 cm, which correspond to ~50 post-shock thermal ion-ion mean free paths. These experimental lengths scales are in reasonable qualitative and quantitative agreement with results from 1D multi-fluid simulations using the Chicago code. However, there are differences between the experimentally-inferred and simulation-predicted ionization states and line emission intensities, particularly in the post-shock region. Overall, the experimental and simulation results are consistent with theoretical predictions that the lighter He ions diffuse farther ahead within the overall shock front than the heavier Ar ions.

physics.plasm-ph↗

arXiv2019

First experiments on Revolver shell collisions at the OMEGA Laser

Results of recent experiments on the OMEGA Laser are presented, demonstrating the ablator-driver shell collision relevant to the outer two shells of the Revolver triple-shell inertial-confinement-fusion concept [K. Molvig et al., PRL~{\bf 116}, 255003 (2016)]. These nested two-shell experiments measured the pre- and post-collision outer-surface trajectory of the 7.19 g/cc chromium inner shell. Measurements of the shell trajectory are in excellent agreement with simulations; the measured outer-surface velocity was $7.52\pm0.59$ cm/$μ$s compared to the simulated value of 7.27 cm/$μ$s. Agreement between the measurements and simulations provides confidence in our ability to model collisions with features which have not been validated previously. Notable features include the absence of $\sim$40 mg/cc foam between shells commonly used in double shell experiments, a dense (7.19 g/cc) inner shell representative of the densities to be used at full scale, approximately mass matched ablator payload and inner shells, and the inclusion of a tamping-layer-like cushion layer for the express purpose of reducing the transfer of high mode growth to the driver shell and mediation of the shell collision. Agreement of experimental measurements with models improves our confidence in the models used to design the Revolver ignition target.

physics.plasm-ph↗

arXiv2018

Simulation Study of the Influence of Experimental Variations on the Structure and Quality of Plasma Liners

Simulation studies of a section of a spherically imploding plasma liner, formed by the merger of six hypersonic plasma jets, have been performed at conditions relevant to the Plasma Liner Experiment (PLX) [S. C. Hsu et al., IEEE Trans. Plasma Sci.~{\bf 46}, 1951 (2018)]. The main aim of simulations was the sensitivity study of the detailed structure of plasma liners and their global properties to experimental mass variations and timing jitter across the six plasma jets. Experimentally observable synthetic quantities have been computed using simulation data and compared with the available experimental data. Simulations predicted that the primary oblique shock wave structure is preserved at small experimental variations. At later phases of the liner implosion, primary shocks and, especially, secondary shocks are more sensitive to experimental variations. These conclusions follow from the simulation data as well as comparisons between synthetic and experimental interferometry and visible images. Small displacements of the shock wave structures may cause significant changes in the synthetic interferometer data at early time. Our studies also showed that the global properties of the plasma liners (averaged Mach number and averaged ram pressure along leading edges of plasma liners) are not very sensitive to experimental variations. Simulation data of the liner structure were largely confirmed by the PLX experimental data.

physics.plasm-ph↗

arXiv2018

Experimental Measurements of Ion Heating in Collisional Plasma Shocks and Interpenetrating Supersonic Plasma Flows

We present time-resolved measurements of ion heating due to collisional plasma shocks and interpenetrating supersonic plasma flows, which are formed by the oblique merging of two coaxial-gun-formed plasma jets. Our study was repeated using four jet species: N, Ar, Kr, and Xe. In conditions with small interpenetration between jets, the observed peak ion temperature Ti is consistent with the predictions of collisional plasma-shock theory, showing a substantial elevation of Ti above the electron temperature Te and also the subsequent decrease of Ti on the classical ion-electron temperature-equilibration time scale. In conditions of significant interpenetration between jets, such that shocks do not apparently form, the observed peak Ti is still appreciable and greater than Te, but much lower than that predicted by collisional plasma-shock theory. Experimental results are compared with multi-fluid plasma simulations.

physics.plasm-ph↗

arXiv2018

Magnetized Plasma Target for Plasma-Jet-Driven Magneto-Inertial Fusion

We identify the desired characteristics and parameters of a beta>1 magnetized plasma, possibly with highly tangled, open field lines, that could be a suitable target to be compressed to fusion conditions by a spherically imploding plasma liner [S. C. Hsu et al., IEEE Trans. Plasma Sci. 40, 1287 (2012)] formed by merging hypersonic plasma jets. This concept is known as plasma-jet-driven magneto-inertial fusion (PJMIF). We set requirements on the target and liner such that (a) compressional heating dominates over thermal transport in the target, and (b) magnetic amplification due to compression dominates over dissipation over the entire implosion. We also evaluate the requirements to avoid drift-instability-induced anomalous transport and current-driven anomalous resistivity in the target. Next, we describe possible approaches to create such a magnetized, beta>1 plasma target. Finally, assuming such a target can be created, we evaluate the feasibility of a proof-of-concept experiment using presently achievable plasma jets to demonstrate target compressional heating at a plasma-liner kinetic energy of <~ 100 kJ (a few hundred times below that needed in a PJMIF reactor).

physics.plasm-ph↗

arXiv2018

Experimental investigation of coaxial-gun-formed plasmas injected into a background transverse magnetic field or plasma

Injection of coaxial-gun-formed magnetized plasmas into a background transverse vacuum magnetic field or into a background magnetized plasma has been studied in the helicon-cathode (HelCat) linear plasma device at the University of New Mexico [M. Gilmore et al., J. Plasma Phys.81, 345810104 (2015)]. Magnetized plasma jet launched into a background transverse magnetic field shows emergent kink stabilization of the jet due to the formation of a sheared flow in the jet above the kink-stabilization threshold $0.1kV_A$ [Y. Zhang et al., Phys. Plasmas 24, 110702 (2017)]. Injection of a spheromak-like plasma into a transverse background magnetic field led to the observation of finger-like structures on the side with a stronger magnetic field null between the spheromak and background field. The finger-like structures are consistent with magneto-Rayleigh-Taylor instability. Jets or spheromaks launched into a background, low-$β$ magnetized plasma show similar behavior as above, respectively, in both cases.

physics.plasm-ph↗

arXiv2018

Physics Criteria for a Subscale Plasma Liner Experiment

Spherically imploding plasma liners, formed by merging hypersonic plasma jets, are a proposed standoff driver to compress magnetized target plasmas to fusion conditions [S. C. Hsu et al., IEEE Trans. Plasma Sci. 40, 1287 (2012)]. In this paper, the parameter space and physics criteria are identified for a subscale, plasma-liner-formation experiment to provide data, e.g., on liner ram-pressure scaling and uniformity, that are relevant for addressing scientific issues of full-scale plasma liners required to achieve fusion conditions. Based on these criteria, we quantitatively estimate the minimum liner kinetic energy and mass needed, which informed the design of a subscale plasma liner experiment now under development.

physics.plasm-ph↗

arXiv2017

Emergent kink stability of a magnetized plasma jet injected into a transverse background magnetic field

We report experimental results on the injection of a magnetized plasma jet into a transverse background magnetic field in the HelCat linear plasma device at the University of New Mexico [M. Gilmore et al., J. Plasma Phys. 81, 345810104 (2015)]. After the plasma jet leaves the plasma-gun muzzle, a tension force arising from an increasing curvature of the background magnetic field induces in the jet a sheared axial-flow gradient above the theoretical kink-stabilization threshold. We observe that this emergent sheared axial flow stabilizes the n=1 kink mode in the jet, whereas a kink instability is observed in the jet when there is no background magnetic field presented.

physics.plasm-ph↗

arXiv2017

Semi-analytic model of plasma-jet-driven magneto-inertial fusion

A semi-analytic model for plasma-jet-driven magneto-inertial fusion is presented. Compressions of a magnetized plasma target by a spherically imploding plasma liner are calculated in one dimension (1D), accounting for compressible hydrodynamics and ionization of the liner material, energy losses due to conduction and radiation, fusion burn and alpha deposition, separate ion and electron temperatures in the target, magnetic pressure, and fuel burn-up. Results show 1D gains of 3-30 at spherical convergence ratio < 15 and 20-40 MJ of liner energy, for cases in which the liner thickness is 1 cm and the initial radius of a preheated magnetized target is 4 cm. Some exploration of parameter space and physics settings is presented. The yields observed suggest that there is a possibility of igniting additional dense fuel layers to reach high gain.

physics.plasm-ph↗

arXiv2015

Observation of Rayleigh-Taylor-Instability Evolution in a Plasma with Magnetic and Viscous Effects

We present time-resolved observations of Rayleigh--Taylor-instability (RTI) evolution at the interface between an unmagnetized plasma jet colliding with a stagnated, magnetized plasma. The observed instability growth time ($\sim 10$~$μ$s) is consistent with the estimated linear RTI growth rate calculated using experimentally inferred values of density ($\sim 10^{14}$~cm$^{-3}$) and deceleration ($\sim 10^9$~m/s$^2$). The observed mode wavelength ($\gtrsim 1$~cm) nearly doubles within a linear growth time. Theoretical estimates of magnetic and viscous stabilization and idealized magnetohydrodynamic simulations including a physical viscosity model both suggest that the observed instability evolution is subject to magnetic and/or viscous effects.

physics.plasm-ph↗

arXiv2015

Experimental characterization of a transition from collisionless to collisional interaction between head-on-merging supersonic plasma jets

We present results from experiments on the head-on merging of two supersonic plasma jets in an initially collisionless regime for the counter-streaming ions. The plasma jets are of either an argon/impurity or hydrogen/impurity mixture and are produced by pulsed-power-driven railguns. Based on time- and space-resolved fast-imaging, multi-chord interferometry, and survey-spectroscopy measurements of the overlapping region between the merging jets, we observe that the jets initially interpenetrate, consistent with calculated inter-jet ion collision lengths, which are long. As the jets interpenetrate, a rising mean-charge state causes a rapid decrease in the inter-jet ion collision length. Finally, the interaction becomes collisional and the jets stagnate, eventually producing structures consistent with collisional shocks. These experimental observations can aid in the validation of plasma collisionality and ionization models for plasmas with complex equations of state.

physics.plasm-ph↗

arXiv2015

Observation of ionization-mediated transition from collisionless interpenetration to collisional stagnation during merging of two supersonic plasmas

We present space- and time-resolved experimental data of head-on-merging, supersonic plasma jets (of an argon/impurity mixture) in an initially collisionless regime for counter-streaming ions. The merging begins with collisionless interpenetration followed by a transition to collisional stagnation. The transition occurs due to an experimentally inferred rising mean-ionization level, which rapidly reduces the counter-streaming ion-ion mean free path. The measurements demonstrate a specific mechanism by which a collisionless interaction transitions to a collisional one and constrain collisionality and ionization models for plasmas with complex equation of state.

physics.plasm-ph↗

arXiv2014

Experimental evidence for collisional shock formation via two obliquely merging supersonic plasma jets

We report spatially resolved measurements of the oblique merging of two supersonic laboratory plasma jets. The jets are formed and launched by pulsed-power-driven railguns using injected argon, and have electron density $\sim 10^{14}$ cm$^{-3}$, electron temperature $\approx 1.4$ eV, ionization fraction near unity, and velocity $\approx 40$ km/s just prior to merging. The jet merging produces a few-cm-thick stagnation layer, as observed in both fast-framing camera images and multi-chord interferometer data, consistent with collisional shock formation [E. C. Merritt et al., Phys. Rev. Lett. {\bf 111}, 085003 (2013)].

physics.plasm-ph↗

arXiv2013

Experimental characterization of the stagnation layer between two obliquely merging supersonic plasma jets

We present spatially resolved measurements characterizing the stagnation layer between two obliquely merging supersonic plasma jets. Intra-jet collisionality is very high ($λ_{ii} \ll 1$mm), but the inter-jet ion-ion mean free paths are on the same order as the stagnation layer thickness (a few cm). Fast-framing camera images show a double-peaked emission profile transverse to the stagnation layer, with the central emission dip consistent with a density dip observed in the interferometer data. We demonstrate that our observations are consistent with collisional oblique shocks.

physics.plasm-ph↗

arXiv2012

Multi-chord fiber-coupled interferometry of supersonic plasma jets and comparisons with synthetic data

A multi-chord fiber-coupled interferometer [Merritt et al., Rev. Sci. Instrum. 83, 033506 (2012)] is being used to make time-resolved density measurements of supersonic argon plasma jets on the Plasma Liner Experiment [Hsu et al., Bull. Amer. Phys. Soc. 56, 307 (2011)]. The long coherence length of the laser (>10 m) allows signal and reference path lengths to be mismatched by many meters without signal degradation, making for a greatly simplified optical layout. Measured interferometry phase shifts are consistent with a partially ionized plasma in which an initially positive phase shift becomes negative when the ionization fraction drops below a certain threshold. In this case, both free electrons and bound electrons in ions and neutral atoms contribute to the index of refraction. This paper illustrates how the interferometry data, aided by numerical modeling, are used to derive total jet density, jet propagation velocity (~15-50 km/s), jet length (~20-100 cm), and 3D expansion.

physics.plasm-ph↗