Sheared flow stabilization experiments in the ZaP flow Z pinch

Shumlak, U.; Nelson, B. A.; Golingo, R.P.; Jackson, S. L.; Crawford, E. A.; Hartog, D. J. Den

doi:10.1063/1.1558294

Cited by 66 publications

(33 citation statements)

References 14 publications

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“…1,2 Static Z pinches are unstable to the m =0 ͑sausage͒ and m =1 ͑kink͒ modes. 8,9 Z pinches with an embedded flow are generated by coupling a coaxial acceleration region with a pinch assembly region. [3][4][5][6][7] The ZaP Flow Z-Pinch experiment at the University of Washington is presently studying the effect of sheared flow on the stability of the Z pinch.…”

Section: Introductionmentioning

confidence: 99%

Formation of a sheared flow Z pinch

2005

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The ZaP Flow Z-Pinch project is experimentally studying the effect of sheared flows on Z-pinch stability. It has been shown theoretically that when dV z / dr exceeds 0.1kV A the kink ͑m =1͒ mode is stabilized. ͓U. Shumlak and C. W. Hartman, Phys. Rev. Lett. 75, 3285 ͑1995͒.͔ Z pinches with an embedded axial flow are formed in ZaP with a coaxial accelerator coupled with a 1 m assembly region. Long-lived, quiescent Z pinches are generated throughout the first half cycle of the current. During the initial plasma acceleration phase, the axial motion of the current sheet is consistent with snowplow models. Magnetic probes in the assembly region measure the azimuthal modes of the magnetic field. The amplitude of the m = 1 mode is proportional to the radial displacement of the Z-pinch plasma current. The magnetic mode levels show a quiescent period which is over 2000 times the growth time of a static Z pinch. The axial velocity is measured along 20 chords through the plasma and deconvolved to provide a radial profile. Using data from multiple pulses, the time evolution of the velocity profile is measured during formation, throughout the quiescent period, and into the transition to instability. The evolution shows that a sheared plasma flow develops as the Z pinch forms. Throughout the quiescent period, the flow shear is greater than the theoretically required threshold for stability. As the flow shear decreases, the magnetic mode fluctuations increase. The coaxial accelerator provides plasma throughout the quiescent period and may explain the evolution of the velocity profile and the sustainment of the flow Z pinch.

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Section: Introductionmentioning

confidence: 99%

Formation of a sheared flow Z pinch

2005

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“…The ZaP experiment (Shumlak et al, 2001(Shumlak et al, , 2003, shown in Fig. 1, produces a hydrogen Z-pinch column (100 cm long and approximately 1 cm radius) with flow velocities on the order of 100-200 km/s (see Table 1 for more information).…”

Section: The Zap Flow Z-pinch Experimentsmentioning

confidence: 99%

Plasma Jet Studies via the Flow Z-Pinch

Shumlak

Nelson

Balick

2006

Astrophys Space Sci

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The ZaP sheared-flow Z-pinch produces high density Z-pinch plasmas that are stable for up to 2000 times the classical instability times. The presence of an embedded radial shear in the axial flow is correlated with the observed stability, and is in agreement with numerical predictions of the stability threshold. The case is made that using a higher-Z working gas will produce supersonic plasma jets, consistent with dimensionless similarity constraints of astrophysical jets. This would allow laboratory testing of some regimes of astrophysical jet theory, computations, and observations.

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“…Measurements and analysis have indicated that ZaP flow Z -pinch plasmas remain stable as a result of sheared axial flows that are generated during the pinch formation process [11], [12], [17], [18]. Instability growth times for static plasmas with similar plasma and magnetic field parameters are on the order of 10 ns.…”

Section: Zap Flow Z -Pinch Experimental Configurationmentioning

confidence: 99%

Calculation of the Equilibrium Evolution of the ZaP Flow $Z$ -Pinch Using a Four-Chord Interferometer

Knecht

Golingo

Nelson

et al. 2015

IEEE Trans. Plasma Sci.

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A four-chord interferometer and measurements from an array of surface-mounted magnetic probes were used in conjunction with equations of radial heat conduction and radial force balance to calculate the equilibrium evolution of a pinch plasma in the ZaP flow Z-pinch. A multiple shooting method was used to solve the nonlinear coupled differential equation system, with ohmic heating and bremsstrahlung radiation as sources and sinks, respectively. Data from a single ZaP pulse are reported including profiles of magnetic field and temperature and their evolution. Profiles are dominated by high thermal conductivity near the axis which quickly decreases with radius. This is due to the plasma being weakly magnetized near the axis which increases thermal conductivity and flattens the temperature profile, but strongly magnetized near the characteristic radius, significantly reducing thermal conductivity and resulting in a large temperature gradient. The equilibrium evolution indicates that plasmas in ZaP heat and compress with increasing current as a result of magnetic compression during the quiescent period.

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Sheared flow stabilization experiments in the ZaP flow Z pinch

Cited by 66 publications

References 14 publications

Formation of a sheared flow Z pinch

Formation of a sheared flow Z pinch

Plasma Jet Studies via the Flow Z-Pinch

Calculation of the Equilibrium Evolution of the ZaP Flow $Z$ -Pinch Using a Four-Chord Interferometer

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