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LONG, STABLE PLASMA GENERATION IN THE ZAP FLOW Z-PINCH*

Author: Brian A. Nelson
Requested Type: Poster Only
Submitted: 2013-01-18 15:45:44

Co-authors: U. Shumlak, R.P. Golingo, M.C. Hughes, S.D. Knecht, W. Lowrie, N. Murakami, H. Stankey, M.C. Paliwoda, E. Ransom, T. Robinson, M.P. Ross, and J. Thiele

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

Abstract Text:
The ZaP Flow Z-pinch^1 at the University of Washington investigates the effect of sheared flows on MHD stability. Axially flowing Z-pinch plasmas are produced that are 100 cm long with a 1 cm radius. The plasma is 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. Profiles of the plasma’s axial flow are measured with a multi-chord ion Doppler spectrometer. A sheared flow profile is observed to be coincident with the quiescent period. The flow profile is well understood and consistent with classical plasma viscosity. Plasma lifetime appears to only be limited by plasma supply and current waveform. Equilibrium is determined by the following 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. A radial heat conduction analysis is performed to calculate equilibrium profiles from the experimental data by assuming Braginskii thermal conductivities and radial force balance. The profiles are corroborated by additional experimental measurements. To confirm the importance of shear flow stabilization, the effect of wall stabilization is investigated by removing large portions of the surrounding conducting wall. The configuration is also computationally modeled to demonstrate no wall effects contributing to observed stability of the Z-pinch plasma.

These studies have led to the design of the newly-funded "ZaP-HD" project, which investigates high energy density plasmas generated using the flow Z-pinch concept. ZaP-HD uses three electrodes to provide individual control of the acceleration and compression of the plasma. 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 under development.

1. U. Shumlak, C.S. Adams, J.M. Blakely, B.-J. Chan, R.P. Golingo, S.D. Knecht, B.A. Nelson, R.J. Oberto, M.R. Sybouts, and G.V. Vogman. Equilibrium, flow shear and stability measurements in the Z-pinch. Nuclear Fusion 49 (7), 075039 (2009).

2. G.V. Vogman and U. Shumlak. Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch. Review of Scientific Instruments 82 (10), 103504 (2011).

3. R.P. Golingo, U. Shumlak, and D.J. Den Hartog. Zeeman splitting measurements in a high-temperature plasma. Review of Scientific Instruments 81 (12), 126104 (2010).

Work supported by a grant from the U.S. DoE

Characterization: 1.1

Comments:
Please place in a different poster session from Nelson et al., "Status of Validation Platform Experiment Simulations by the PSI-Center"