About

Professor Uri Shumlak completed his undergraduate work at Texas A&M University and obtained his PhD in Nuclear Engineering from the University of California at Berkeley. Following his graduate studies, he was a National Research Council postdoctoral fellow at the Air Force Phillips Laboratory in Albuquerque, New Mexico, where he developed MACH3, a 3-D, time-dependent magnetofluid code for non-ideal plasmas in complex geometries. He joined the University of Washington after leaving the Phillips Lab and maintains close ties to the Air Force Research Lab, often supporting their research efforts. His research areas include plasma physics, theoretical and computational plasma modeling, innovative magnetic plasma confinement for fusion energy, and electric propulsion. His work involves both theoretical and experimental investigations, such as the stabilizing effects of sheared flows in magnetically confined plasmas, with applications in space exploration and fusion energy sources. He has developed advanced plasma modeling algorithms and novel electric propulsion devices, including a high current ion source using ultrasonic actuators. Professor Shumlak is a Fellow of the American Physical Society, an Associate Fellow of the American Institute of Aeronautics and Astronautics, and a Senior Member of the IEEE. He is also a co-founder of Zap Energy, a spin-out company from the University of Washington focused on developing commercial fusion applications.

Research topics

• Physics
• Nuclear physics
• Atomic physics
• Mechanics
• Chemistry
• Optics
• Nuclear engineering
• Materials science
• Engineering
• Quantum mechanics
• Electrical engineering

Selected publications

• Experimental investigation of plasma–electrode interactions on the ZaP-HD sheared-flow-stabilized Z-pinch device

  Physics of Plasmas · 2026-03-01

  articleOpen accessSenior author

  The ZaP-HD sheared-flow-stabilized Z-pinch device is a testbed for experimental investigation of plasma–electrode interactions. The graphite electrode is exposed to a high-temperature, high-density Z-pinch plasma while supplying large pinch currents. In situ measurements of the gross carbon erosion flux obtained with S/XB spectroscopy exceed the expected flux from physical sputtering but have reasonable agreement with the expected sublimation flux. Comparison of the ionization mean free paths of neutrals produced through both erosion processes shows that sublimated carbon is ionized within the sheath, while sputtered carbon is ionized beyond the sheath. This suggests a process of electrode recycling and self-healing through redeposition. The sputtered carbon is primarily responsible for net erosion. Ex situ analysis of electrode material is enabled by designing a removable coupon. Three different experimental campaigns varied the pinch current and number of pulses for each coupon. Net mass loss measurements support the physical picture of electrode recycling. Erosion rates range from 0.01 to 0.1 mg/C, which are comparable to existing arc discharge devices. Measurements of the microscopic surface morphology and roughness reveal irregular consolidated structures and general smoothing, except at high particle fluence. Crack formation suggests the importance of repetitive thermal cycles. Definitive features of sputtering such as pitting and cratering are absent, although further study is needed to attribute the observed changes to other processes. These results indicate some alignment with erosion processes in high-powered arc discharges, which successfully operate solid electrodes in extreme environments. This provides confidence in managing electrode erosion for fusion Z-pinch devices.

  PublisherDOI

• Diagnostic Overview of the FuZE-Q Sheared-Flow-Stabilized Z-Pinch Experiment

  2025-06-15

  articleSenior author

  FuZE-Q, a platform for scaling the sheared-flow-stabilized (SFS) Z-pinch to higher fusion output at Zap Energy, employs a suite of advanced diagnostics to characterize plasma performance, including fusion gain and triple product [Shumlak, Meier, Levitt, Fusion Sci. Technol. (2024)]. Arrays of magnetic probes, scintillating PMT and activation neutron detectors, x-ray detectors, high-speed cameras, and a multi-point Thomson scattering system are all regularly fielded on the FuZE-Q device. This presentation highlights results from interferometric and spectroscopic systems including ion Doppler spectroscopy (IDS), extreme ultraviolet (EUV) and visible spectrometers, narrowband, filtered photodiodes, line-integrated heterodyne interferometry, and digital holographic interferometry (DHI). Arrays of interferometry chords are used to estimate mass flux from the accelerator region into the pinch. Abel-inverted, 2D interferograms yield high resolution density profiles which suggest central pinch densities of up to 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">24</sup> m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup>. Local, sheared flow profiles are measured using the ion feature in Thomson scattering spectra. Additionally, tracking the temporal evolution of multiple impurity emission lines informs the evolution of plasma temperature in the compression region.

  PublisherDOI

• Experimental investigation of plasma-electrode interactions on the ZaP-HD sheared-flow-stabilized Z-pinch device

  ArXiv.org · 2025-11-01

  preprintOpen accessSenior author

  The ZaP-HD sheared-flow-stabilized (SFS) Z-pinch device is a testbed for experimental investigation of plasma-electrode interactions. The graphite electrode is exposed to a high temperature, high density Z-pinch plasma while supplying large pinch currents. In-situ measurements of the gross carbon erosion flux obtained with S/XB spectroscopy exceed the expected flux from physical sputtering, but have reasonable agreement with the expected sublimation flux. Comparison of the ionization mean free paths of neutrals produced through both erosion processes shows that sublimated carbon is ionized within the sheath while sputtered carbon is ionized beyond the sheath. This suggests a process of electrode recycling and self-healing through redeposition. The sputtered carbon is primarily responsible for net erosion. Ex-situ analysis of electrode material is enabled by the design of a removable coupon. Three different plasma exposure conditions varied the pinch current and number of pulses. Net mass loss measurements support the physical picture of electrode recycling. Erosion rates range from 0.01 to 0.1 mg/C, which are comparable to existing arc discharge devices. Measurements of the microscopic surface morphology and roughness reveal irregular consolidated structures and general smoothing except at high particle fluence. Crack formation suggests the importance of repetitive thermal cycles. Definitive features of sputtering such as pitting and cratering are absent, although further study is needed to attribute the observed changes to other processes. These results indicate some alignment with erosion processes in high-powered arc discharges, which successfully operate solid electrodes in extreme environments. This provides confidence in managing electrode erosion in the SFS Z-pinch configuration.

  PublisherOA PDFDOI

• Overview of Flow Z-Pinch Theory and Modeling at Zap Energy

  2025-06-15

  article

  Zap Energy is developing the sheared-flow-stabilized (SFS) Z pinch for commercial fusion energy purposes [Shumlak J. Appl. Phys. 2020]. Our research and development strategy involves building predictive understanding of SFS Z-pinch physics through coupled experimental and modeling efforts. Modeling has been focused on 2D MHD whole-device simulations [Datta et al. Nucl. Fusion 2024], including full circuit-coupled models, providing an excellent match with experimental results. Parallel efforts are under way to develop high-fidelity physics models including: MHD, two-fluid, and kinetic modeling of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{m}=1$</tex> kink stabilization; plasma-neutral modeling of accelerator behavior, including snowplow and deflagration phases of operation; and pure theory development related to betatron particle physics in the Z-pinch core. As high-fidelity modeling capabilities mature, they will be incorporated in whole-device simulations and validated against experimental data.

  PublisherDOI

• Spectroscopic measurements of graphite electrode erosion on the ZaP-HD sheared-flow-stabilized Z-pinch device

  ArXiv.org · 2025-10-03

  preprintOpen accessSenior author

  The ionizations per photon, or S/XB, method uses spectroscopic measurements of radiating impurity ions to determine the influx from a solid surface. It is highly useful as a non-perturbing, in-situ measure of the gross erosion flux of plasma-facing components (PFCs). In sheared-flow-stabilized (SFS) Z-pinch devices, the electrode supplies the plasma current and directly contacts the core Z-pinch plasma. Electrode erosion due to the large particle and heat fluxes affects electrode durability, which is an important factor in existing and future devices. An improved understanding of these plasma-electrode interactions is required, in particular as energy density increases. Experiments on the ZaP-HD device investigate erosion of the graphite electrode by applying the S/XB method for C-III emission at 229.7 nm. The S/XB coefficients are determined from electron density and temperature profiles obtained from Digital Holographic Interferometry (DHI) measurements. An approach for expanding these profiles to represent plasma contacting the electrode is described. In both cases, the measured erosion fluxes are on the order of 10$^{30}$-10$^{31}$ atoms m$^{-2}$s$^{-1}$. These values are significantly larger than the expected erosion flux due to physical sputtering of H$^+$ ions on carbon, but are comparable to theoretical sublimation fluxes. This suggests that the source of carbon erosion flux is primarily from sublimation as opposed to sputtering. The dominance of sublimation over sputtering processes implies a difference in energy of the eroded neutrals which may provide insight on redeposition and net erosion behavior.

  PublisherOA PDFDOI

• Control of kinetic plasma instabilities by laser fields

  ArXiv.org · 2025-09-27

  preprintOpen access

  We study the possibility of controlling kinetic plasma instabilities by using lasers to apply external electromagnetic fields. We derive the dispersion relation for the corresponding mathematical description, a reduced Vlasov--Maxwell system, by extending the well-known Penrose condition. It is observed that, under very mild assumptions, the dispersion relation decouples into two parts. The first part is identical to the classic Penrose condition for the Vlasov--Poisson system, while the second part describes the influence of the laser on the transverse dynamics (e.g. a Weibel instability). In particular, this means that the longitudinal dynamics (e.g. a two-stream instability) can not be stabilized in this manner as far as linear theory is concerned. We show, however, that nonlinear effects can be used to couple the two parts and achieve effective control. This is done by determining the control parameters (i.e. the form of the external electric and magnetic fields) by solving a PDE-constrained optimization problem.

  PublisherOA PDFDOI

• Spectroscopic Analysis of Erosion Rate from Electrode Surfaces on the ZaP-HD Device

  2025-01-01

  articleSenior author

  Plasma interactions with material surfaces introduce impurities into plasma devices that contribute to radiative losses and limit operational lifetimes. The development of a diagnostic for monitoring erosion yields is crucial for understanding impurity dynamics in plasmas and for the evaluation of mitigation methods to minimize electrode erosion. Spectroscopy provides a non-perturbative tool to quantify impurity production rates and transport. The ionization per photon (S/XB) method in spectroscopy correlates line emission intensity to particle flux using empirical coefficients based on temperature and density. On the ZaP-HD Device, the graphite cathode that interacts with high-temperature, high-density plasmas is prone to physical erosion. Initial efforts in implementing an SXB calibration to an existing spectrometer and photomultiplier tube (PMT) setup are presented. Preliminary data analysis of carbon erosion rate using calibrated data and S/XB coefficients is discussed, with future work extending the diagnostic system to monitor additional carbon charge states and emissions at varying axial locations.

  PublisherDOI

• Time-resolved measurement of neutron energy isotropy in a sheared-flow-stabilized Z pinch

  Nuclear Fusion · 2025-01-31 · 3 citations

  articleOpen accessSenior author

  Abstract Previous measurements of neutron energy using fast plastic scintillators while operating the Fusion Z Pinch Experiment (FuZE) constrained the energy of any yield-producing deuteron beams to less than 4.65 keV. FuZE has since been operated at increasingly higher input power, resulting in increased plasma current and larger fusion neutron yields. A detailed experimental study of the neutron energy isotropy in these regimes applies more stringent limits to possible contributions from beam-target fusion. The FuZE device operated at −25 kV charge voltage has resulted in average plasma currents of 370 kA and D–D fusion neutron yields of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>4</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>7</mml:mn> </mml:msup> <mml:mo>±</mml:mo> <mml:mn>4</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>6</mml:mn> </mml:msup> </mml:mrow> </mml:math> neutrons per discharge. Measurements of the neutron energy isotropy under these operating conditions demonstrates the energy of deuteron beams is less than <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>7.4</mml:mn> <mml:mo>±</mml:mo> <mml:msup> <mml:mn>5.6</mml:mn> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mi>stat</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:msup> <mml:mo>±</mml:mo> <mml:msup> <mml:mn>3.7</mml:mn> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mi>syst</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> keV. Characterization of the detector response has reduced the number of free parameters in the fit of the neutron energy distribution, improving the confidence in the forward-fit method. Gamma backgrounds have been measured and the impact of these contributions on the isotropy results have been studied. Additionally, a time dependent measurement of the isotropy has been resolved for the first time, indicating increases to possible deuteron beam energies at late times. This suggests the possible growth of m = 0 instabilities at the end of the main radiation event but confirms that the majority of the neutron production exhibits isotropy consistent with thermonuclear origin.

  PublisherDOI

• Effects of transitional orbit magnetization on transport and current in Z pinches

  Physics of Plasmas · 2025-10-01

  articleOpen accessSenior author

  The azimuthal self-magnetic field of the ideal Z pinch contains a central magnetic null. Trajectories around this null govern transport in the core. Particles follow cyclotron orbits when the guiding-center approximation holds. Approaching the field null, where the ordinary guiding-center regime breaks down, particles exhibit trajectories called, in some historical contexts, betatron orbits. We quantify transitional magnetization between cyclotron and betatron orbits by a magnetization parameter that decomposes phase space into these orbit regimes. Considering the distribution of all orbits, this phase-space decomposition reveals a transitional magnetization region wherein both populations coexist. Classical magnetized transport theory fails within this region, where the diamagnetic drift reverses. The drift flux is instead supported by the flux of betatron orbits. Magnetic field dependent quantities which appear to diverge at the field null, such as cross field drift due to resistive electric fields, are physically resolved by the transitional magnetization of orbits. These transport modifications are governed solely by the number density per unit length in the ideal pinch.

  PublisherDOI

• Three-Dimensional Hybrid Kinetic Simulations of Flow Z-Pinch Plasma Stability

  2025-06-15

  articleSenior author

  Understanding Z-pinch stability, particularly of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{m}=0$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{m}=1$</tex> modes, is crucial for the success of sheared-flow-stabilized Z-pinch fusion approach being pursued for commercial energy generation by Zap Energy. While <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{m}=0$</tex> stabilization has been studied with PIC [Tummel et al. PoP 2019], research on <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$m=1$</tex> has been more limited. Hybrid kinetic modeling has been applied to study <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{m}=1$</tex>, including works with sheared flow [Sotnikov et al. PoP 2004] and without [Arber et al. PRL 1995]. To supplement two-fluid modeling of sheared-flow stabilization [Meier & Shumlak PoP 2021], Zap Energy researchers are performing high-fidelity, three-dimensional simulations of sheared-flow Z pinch stability with a hybrid kinetic algorithm in the WarpX PIC code [Fedeli et al. IEEE 2022], including ion kinetic behavior, but using an Ohm's law representation in place of electron kinetics. We aim to quantify the level sheared flow required to provide linear stability across the wavelength spectrum and for many values of the ratio of pinch size to Larmor radius and for many values of resistivity. We first show benchmark results comparing results from the WarpX code with the results of Sotnikov. Next we compare these results with two-fluid results and with six-dimensional continuum kinetic results. We also report on the nonlinear evolution and whether the nonlinear state is quasi-stable.

  PublisherDOI

Recent grants

• Multiscale Phenomena in Plasmas from Collisional to Collisionless Regimes

  NSF · $360k · 2021–2025

Frequent coauthors

• B. A. Nelson

  NOAA National Centers for Environmental Information

  160 shared

• R.P. Golingo

  University of Washington

  134 shared

• H. S. McLean

  Lawrence Livermore National Laboratory

  69 shared

• Eleanor Forbes

  60 shared

• B.A. Nelson

  58 shared

• E.L. Claveau

  Plasma Technology (United States)

  55 shared

• A.D. Stepanov

  51 shared

• D. P. Higginson

  Lawrence Livermore National Laboratory

  49 shared

Education

• B.S.

  Texas A & M University

• Ph.D., Nuclear Engineering

  University of California at Berkeley

Awards & honors

• Fellow of the American Physical Society
• Associate Fellow of the American Institute of Aeronautics an…
• Senior Member of the Institute of Electrical and Electronics…