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Formation and Stabilization in the ZaP Flow Z-Pinch

Author: Uri Shumlak
Requested Type: Consider for Invited
Submitted: 2009-12-04 18:22:14

Co-authors: R.P. Golingo, M. Hughes, S.D. Knecht, B.A. Nelson, R.J. Oberto, J.L. Rohrbach, G. Shah, G.V. Vogman

Contact Info:
University of Washington
120 AERB, Box 352250
Seattle, WA   98195-2
USA

Abstract Text:
The ZaP Flow Z-pinch experiment at the University of Washington investigates the effect of sheared flows on MHD stability. An axially flowing Z-pinch plasma is produced by coupling a coaxial accelerator with a pinch assembly region. The resulting Z-pinch plasma is 100 cm long with a 1 cm radius. After assembly, the plasma is magnetically confined for an extended quiescent period during which the magnetic mode activity is significantly reduced. Optical images of the plasma also indicate a stationary, confined plasma structure during this period. The plasma structure is highly dynamic at other times with fluctuation times less than a microsecond. The plasma flow profiles show a shear in the axial flow (dv_z/dr) that is large during the quiescent period. The shear is small before and after the quiescent period, even though the axial flow speed may be large. The coincidence between stability and flow shear appears consistent for a variety of experimental operating conditions. Determining causality is a current focus of investigations. Temperatures in the stationary, confined plasma have been measured at 150 - 250 eV during the quiescent period. Recent experimental modifications have increased the size of the inner electrode to study the heating mechanisms in the Z-pinch plasma. Theoretical analysis and computational simulations indicate that adiabatic compression during the formation and sustainment is the primary mechanism. The plasma temperature should theoretically increase by 70% in a two-dimensional radial compression when the inner electrode radius is increased by 50%. Comparisons with experimental results will be presented. Experimental equilibrium properties are measured using interferometry for density, Doppler line broadening for ion temperature, Thomson scattering for electron temperature, Zeeman splitting of impurity radiation lines for internal magnetic field measurements, and probes for external magnetic field measurements. Varying the Z-pinch equilibrium properties over a wide range allows a more thorough investigation of shear flow stabilization and fundamental heating mechanisms in the plasma. An overview of the experimental program, results, and future work will be presented.

Characterization: A2,E3

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