Formation of a sheared flow Z pinch

Abstract

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.

Hypersonic Buckshot: Astrophysical Jets as Heterogeneous Collimated Plasmoids

“…The saturation of the instability rapidly transforms the jet into a sequence of collimated chains of knots which propagate with a range of velocities. Similar fragmented chains have been seen in other pulsed power experiments (Golingo et al 2005). In the last section of the paper, we discuss some possible mechanisms by which subradial knots are created in jets.…”

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“…The details of the formation process and experimental measurements are provided in Refs. [1] and [11], and references therein.…”

Heights integrated model as instrument for simulation of hydrodynamic, radiation transport, and heat conduction phenomena of laser-produced plasma in EUV applications.

“…The ideal MHD equation set (1.20) can be used to solve a limited physical problem such as a dense space plasma [10,14,15], to conduct theoretical investigations of instabilities [16][17][18] or to simplify real devices [19,20]. Key in modeling DPP or LPP devices, however, is representing the correct energy exchange and taking into account the main dissipative processes.…”