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sdk_icc_writeup.pdf2011-08-26 18:08:46Sean Knecht
sdk_icc_2011_presentation.pdf2011-08-26 18:08:21Sean Knecht

Overview of the ZaP Flow Z-pinch Experiment

Author: Sean D Knecht
Requested Type: Consider for Invited
Submitted: 2011-06-10 14:03:19

Co-authors: U. Shumlak, R.P. Golingo, B.A. Nelson, M.P. Ross, M.C. Hughes, R.J. Oberto

Contact Info:
University of Washington
120 AERB
Seattle, WA   98105

Abstract Text:
The ZaP Flow Z-pinch experiment at the University of Washington is a basic plasma physics experiment that uses sheared axial flows to maintain the gross stability of a Z-pinch plasma. Z-pinches generated are approximately 1 cm in radius, greater than 100 cm long and exhibit stability for many Alfven transit times. Measurements of the axial flow velocity profile indicate that low magnetic mode fluctuations are coincident with a sheared profile. The flow profile is uniform near the axis of the pinch with the shear localized near the edges. This type of profile agrees with classical viscosity calculations which suggest that flow velocity near the axis should equilibrate due to collisions. Investigation of pinch stability in the absence of a close-fitting conducting wall suggests that a wall is not necessary when flow shear is present, agreeing with theoretical predictions. Further, multiple diagnostics indicate evidence of a coherent pinch structure with a length greater than 100 cm that persists for many flow-through times: a linear array of magnetic probes along the length of experiment shows an axially uniform magnetic field structure; azimuthal arrays of magnetic probes at multiple axial locations show decreased magnetic fluctuations concurrently throughout a plasma pulse; two-chord interferometry and visible light emissions indicate a highly-pinched plasma located on the axis of the machine; a Rogowski coil measuring end-loss current and a gridded energy analyzer show plasma exhaust through a hole in the outer electrode end-wall correlated with periods of stability.

The effects of adiabatic compression on the pinch are investigated with two electrode configurations: a 10 cm diameter inner electrode and a 16 cm diameter inner electrode. The larger inner electrode is predicted to increase temperature significantly. A two-point Thomson scattering system is used to measure electron temperature and relative electron density at two radial locations in the pinch. These measurements indicate increased temperature for the 16 cm inner electrode. Ion temperature measurements from Doppler broadening and force balance calculations agree with the Thomson scattering measurements.

Characterization: A2


University of Washington

Workshop on Innovation in Fusion Science (ICC2011) and
US-Japan Workshop on Compact Torus Plasma
August 16-19, 2011
Seattle, Washington

ICC 2011