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Title: Increasing plasma parameters using sheared flow stabilization of a Z-pinch

ORCiD logo [1];  [1];  [1];  [1];  [1];  [1];  [1]; ORCiD logo [1];  [1]
  1. Aerospace and Energetics Research Program, University of Washington, Seattle, Washington 98195-2400, USA
Publication Date:
Sponsoring Org.:
USDOE Advanced Research Projects Agency - Energy (ARPA-E); USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
Grant/Contract Number:
NA0001860; AR-0000571; FG02-04ER54756
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 5; Related Information: CHORUS Timestamp: 2018-02-14 23:54:24; Journal ID: ISSN 1070-664X
American Institute of Physics
Country of Publication:
United States

Citation Formats

Shumlak, U., Nelson, B. A., Claveau, E. L., Forbes, E. G., Golingo, R. P., Hughes, M. C., Oberto, R. J., Ross, M. P., and Weber, T. R. Increasing plasma parameters using sheared flow stabilization of a Z-pinch. United States: N. p., 2017. Web. doi:10.1063/1.4977468.
Shumlak, U., Nelson, B. A., Claveau, E. L., Forbes, E. G., Golingo, R. P., Hughes, M. C., Oberto, R. J., Ross, M. P., & Weber, T. R. Increasing plasma parameters using sheared flow stabilization of a Z-pinch. United States. doi:10.1063/1.4977468.
Shumlak, U., Nelson, B. A., Claveau, E. L., Forbes, E. G., Golingo, R. P., Hughes, M. C., Oberto, R. J., Ross, M. P., and Weber, T. R. Mon . "Increasing plasma parameters using sheared flow stabilization of a Z-pinch". United States. doi:10.1063/1.4977468.
title = {Increasing plasma parameters using sheared flow stabilization of a Z-pinch},
author = {Shumlak, U. and Nelson, B. A. and Claveau, E. L. and Forbes, E. G. and Golingo, R. P. and Hughes, M. C. and Oberto, R. J. and Ross, M. P. and Weber, T. R.},
abstractNote = {},
doi = {10.1063/1.4977468},
journal = {Physics of Plasmas},
number = 5,
volume = 24,
place = {United States},
year = {Mon May 01 00:00:00 EDT 2017},
month = {Mon May 01 00:00:00 EDT 2017}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1063/1.4977468

Citation Metrics:
Cited by: 1work
Citation information provided by
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  • The ZaP Flow Z-Pinch research project[1] at the University of Washington investigates the effect of sheared flows on MHD instabilities. Axially flowing Z-pinch plasmas are produced that are 100 cm long with a 1 cm radius. The plasma remains quiescent for many radial Alfvén times and axial flow times. The quiescent periods are characterized by low magnetic mode activity measured at several locations along the plasma column and by stationary visible plasma emission. Plasma evolution is modeled with high-resolution simulation codes – Mach2, WARPX, NIMROD, and HiFi. Plasma flow profiles are experimentally measured with a multi-chord ion Doppler spectrometer. Amore » sheared flow profile is observed to be coincident with the quiescent period, and is consistent with classical plasma viscosity. Equilibrium is determined by diagnostic measurements: interferometry for density; spectroscopy for ion temperature, plasma flow, and density[2]; Thomson scattering for electron temperature; Zeeman splitting for internal magnetic field measurements[3]; and fast framing photography for global structure. Wall stabilization has been investigated computationally and experimentally by removing 70% of the surrounding conducting wall to demonstrate no change in stability behavior.[4] Experimental evidence suggests that the plasma lifetime is only limited by plasma supply and current waveform. The flow Z-pinch concept provides an approach to achieve high energy density plasmas,[5] which are large, easy to diagnose, and persist for extended durations. A new experiment, ZaP-HD, has been built to investigate this approach by separating the flow Z-pinch formation from the radial compression using a triaxial-electrode configuration. This innovation allows more detailed investigations of the sheared flow stabilizing effect, and it allows compression to much higher densities than previously achieved on ZaP by reducing the linear density and increasing the pinch current. Experimental results and scaling analyses will be presented. In addition to studying fundamental plasma science and high energy density physics, the ZaP and ZaP-HD experiments can be applied to laboratory astrophysics.« less
  • A linear analysis of the ideal magnetohydrodynamic (MHD) stability of the Z-pinch is presented in which plasma flows are included in the equilibrium. With sheared axial flows it is found that substantial stabilization of internal modes is possible for some equilibrium profiles. For this to occur equilibria with a change in fluid velocity across the pinch radius of about Mach 2 are required. However, this ignores the surrounding vacuum and for the more realistic free boundary modes flows of about Mach 4 are required to stabilize all global MHD modes. This stabilization of MHD modes is not observed for allmore » equilibria however. This fact, combined with the supersonic flow speeds required for stability, make it unlikely that a Z-pinch could in practice be stabilized by the introduction of sheared flow. {copyright} {ital 1996 American Institute of Physics.}« less
  • The ZaP Flow Z-Pinch project is experimentally studying the effect of sheared flows on Z-pinch stability. It has been shown theoretically that when dV{sub z}/dr exceeds 0.1kV{sub A} the kink (m=1) mode is stabilized. [U. Shumlak and C. W. Hartman, Phys. Rev. Lett. 75, 3285 (1995).] Z pinches with an embedded axial flow are formed in ZaP with a coaxial accelerator coupled with a 1 m assembly region. Long-lived, quiescent Z pinches are generated throughout the first half cycle of the current. During the initial plasma acceleration phase, the axial motion of the current sheet is consistent with snowplow models.more » Magnetic probes in the assembly region measure the azimuthal modes of the magnetic field. The amplitude of the m=1 mode is proportional to the radial displacement of the Z-pinch plasma current. The magnetic mode levels show a quiescent period which is over 2000 times the growth time of a static Z pinch. The axial velocity is measured along 20 chords through the plasma and deconvolved to provide a radial profile. Using data from multiple pulses, the time evolution of the velocity profile is measured during formation, throughout the quiescent period, and into the transition to instability. The evolution shows that a sheared plasma flow develops as the Z pinch forms. Throughout the quiescent period, the flow shear is greater than the theoretically required threshold for stability. As the flow shear decreases, the magnetic mode fluctuations increase. The coaxial accelerator provides plasma throughout the quiescent period and may explain the evolution of the velocity profile and the sustainment of the flow Z pinch.« less
  • A holographic interferometer is used to determine the radial electron number density profile of a sheared-flow Z pinch. Chord-integrated density information is recorded during a plasma pulse using the expanded beam of a pulsed ruby laser and holographic techniques. An Interactive Data Language (IDL) computer routine that requires only minimal user interaction is used to measure the resulting fringe shift in the reconstructed interferogram. This chord-integrated density information is inverted using an Abel inversion to determine the radial electron density profile. The density profiles obtained show a radially symmetric plasma column with an electron density of 10{sup 16}-10{sup 17} cm{supmore » -3} above the background plasma density. Holographic measurements are made at different times on separate plasma pulses to track the evolution of the density profile over time. These measurements are corroborated by time-dependent measurements made using a He-Ne interferometer.« less
  • It is well known that a static (i.e., v=0) closed field line configuration, such as a levitated dipole, or a hard-core Z pinch, can be stabilized against ideal magnetohydrodynamic (MHD) interchange modes when the edge pressure gradient is sufficiently weak. The stabilizing effect is provided by plasma compressibility. However, many laboratory plasmas exhibit a sheared velocity flow (i.e., n{center_dot}{nabla}v{ne}0), and this flow may affect the marginal stability boundary. The present work addresses this issue by an analysis of the effect of axially sheared flow on interchange stability in a hard-core Z pinch, a cylindrical model for the levitated dipole configuration.more » Specifically, the goal is to learn whether sheared flow is favorable, unfavorable, or neutral with respect to MHD stability. Analytic calculations of marginal stability for several idealistic velocity profiles show that all three options are possible depending on the shape of the shear profile. This variability reflects the competition between the destabilizing Kelvin-Helmholtz effect and the fact that shear makes it more difficult for interchange perturbations to form. Numerical calculation are also presented for more realistic experimental profiles and compared with the results for the idealized analytic profiles.« less