[show abstract][hide abstract] ABSTRACT: The ZaP flow Z-pinch experiment at the University of Washington investigates the innovative plasma confinement concept of
using sheared flows to stabilize an otherwise unstable configuration. The ZaP experiment generates an axially flowing Z-pinch
that is 1m long with a 1cm radius with a coaxial accelerator coupled to a pinch assembly chamber. Magnetic probes measure
the fluctuation levels of the azimuthal modes m=1, 2, and 3. After assembly, the plasma is magnetically confined for an extended quiescent period where the mode activity
is significantly reduced. Experimental measurements show a sheared flow profile that is coincident with the low magnetic fluctuations
during the quiescent period. Recent experimental modifications produce more energetic Z-pinch plasmas that exhibit the same
general behavior. The plasma equilibrium is characterized with a suite of diagnostics that measure the plasma density, magnetic
field, ion and electron temperatures, in addition to plasma flow. The equilibrium is shown to satisfy radial force balance.
Journal of Fusion Energy 04/2012; 28(2):208-211. · 1.00 Impact Factor
[show abstract][hide abstract] ABSTRACT: The stabilizing effect of a sheared axial flow is investigated in the ZaP flow Z-pinch experiment at the University of Washington. Long-lived, hydrogen Z-pinch plasmas are generated that are 1 m long with an approximately 10 mm radius and exhibit gross stability for many Alfvén transit times. Large magnetic fluctuations occur during pinch assembly, after which the amplitude and frequency of the fluctuations diminish. This stable behaviour continues for an extended quiescent period. At the end of the quiescent period, fluctuation levels increase in magnitude and frequency. Axial flow profiles are determined by measuring the Doppler shift of plasma impurity lines using a 20-chord spectrometer. Experimental measurements show a sheared flow that is coincident with low magnetic fluctuations during the quiescent period. The experimental flow shear exceeds the theoretical threshold during the quiescent period, and the flow shear is lower than the theoretical threshold at other times. The observed plasma behaviour and correlation between the sheared flow and stability persists as the amount of injected neutral gas and experimental geometry are varied. Computer simulations using experimentally observed plasma profiles show a consistent sheared flow stabilization effect. Plasma pinch parameters are measured independently to demonstrate an equilibrium consistent with radial force balance.