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nelson_epr14.pdf2014-08-14 09:08:28Brian Nelson

Sheared-Flow Stabilized Z-pinch Studies: ZaP and ZaP-High Density Experiments

Author: Brian A Nelson
Requested Type: Consider for Invited
Submitted: 2014-05-29 11:32:41

Co-authors: U.Shumlak, R.P.Golingo, M.C.Hughes, M.P.Ross, J.Chadney, S.D.Knecht, W.Lowrie, C.Bowers, S.A.Doty, E.G.Forbes, S.Funke, D.Goldstone, B.Kim, K.K.Lambert, and J.Weed

Contact Info:
University of Washington
120 AERB, 352250
Seattle, Washington   98195
USA

Abstract Text:
The ZaP project investigates the use of velocity shear to mitigate MHD instabilities. The ZaP experiment produces axially flowing Z-pinch plasmas 100 cm long and 1 cm radius. The plasma is quiescent for many Alfvén times and axial flow times, characterized by low magnetic mode activity measured at several axial locations and by stationary visible plasma emission. A sheared flow profile is coincident with the quiescent period, and is consistent with classical plasma viscosity. Plasma lifetime appears to only be limited by plasma supply and the duration of the current. Equilibrium is determined by the following diagnostic measurements: multi-chord interferometry for density; spectroscopy for Ti, plasma flow, and density; Thomson scattering for Te; Zeeman splitting for internal B fields; and fast-framing photography for global structure. To confirm the importance of shear flow stabilization, the effect of wall stabilization was demonstrated by removing large portions of the surrounding conducting wall. 2D Mach2 simulations agree with experimental results and demonstrate the formation and sustainment of a sheared-flow stabilized Z-pinch. 3D HiFi simulations demonstrate wall effects do not contribute to observed stability of the Z-pinch plasma.
The ZaP-HD experiment is exploring the compression of a shear-stabilized Z-pinch to higher energy densities than were possible on the previous ZaP machine. ZaP-HD has a triaxial-electrode configuration, allowing separation between acceleration and compression power supplies. This innovation allows compression to much higher densities than previously achieved on ZaP (a factor of three to ten times larger, 1-3x10^{18} cm^{-3}) by reducing the linear density and increasing the pinch current. ZaP-HD has several large viewports allowing optical access to the entire assembly for the existing diagnostics, as well as a new digital holography system, presently being implemented.
Work supported by grants from the U.S. DoE & NNSA

Characterization: 1.1

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Workshop on Exploratory Topics in Plasma and Fusion Research (EPR) and US-Japan Compact Torus (CT) Workshop
August 5-8, 2014
Madison, Wisconsin

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