STM-D-1077Paper2003On the bench now

Sheared flow stabilization experiments in the ZaP flow Z pinch

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

Abstract and summary · read the original at the source · none found

In one page

Run a large current down a thin column of plasma and the column squeezes itself: that is a Z pinch, and it has been the most tempting and most disappointing route to fusion since the 1950s, because the column kinks sideways and destroys itself in nanoseconds. Uri Shumlak’s team at the University of Washington report an answer that adds no magnets at all. Theory in a linearised ideal magnetohydrodynamic model says that if the plasma flows along its own axis, fast in the middle and slower at the rim, the kink is held still once that shear passes a threshold. Their ZaP machine tests it: a metre-long coaxial accelerator throws plasma into a pinch about 50 centimetres long and a centimetre across, magnetic probes ringed around the midplane watch for the kink, and cameras, an interferometer and Doppler measurements watch the column itself. A quiet period appears, and the flow shear is large exactly when the column is quiet.

Why it matters hereChapter 12 wants fusion conditions from the smallest and simplest possible machine, and a Z pinch is the simplest there is — the trouble has always been holding it still. Chapter 9 is about plasma that organises and keeps its own shape, and this is a column held straight for hundreds of times its own instability growth time by nothing but the velocity profile it carries.

What it claims

01A linearised ideal magnetohydrodynamic model, solved numerically, shows that a sheared axial flow stabilises the m equals 1 kink instability in a Z pinch once the shear exceeds a threshold.Abstract, first sentence
Published and peer-reviewed
02The effect is tested on real hardware: the ZaP Flow Z-pinch experiment at the University of Washington generates an axially flowing Z pinch with a one-metre coaxial accelerator coupled to a pinch assembly chamber, and the plasma assembles into a pinch 50 centimetres long with a radius of approximately 1 centimetre.Abstract, third and fourth sentences
On the bench now
03An azimuthal array of surface-mounted magnetic probes at the midplane of the pinch measures the fluctuation levels of the azimuthal modes m equals 1, 2 and 3, and after the pinch assembles a quiescent period is found in which the mode activity is significantly reduced.Abstract, fifth and sixth sentences
Published and peer-reviewed
04Two independent optical diagnostics agree with the magnetic probes: images from a fast framing camera and from a ruby holographic interferometer show a stable, discrete pinch plasma during the quiescent period.Abstract, seventh sentence
Published and peer-reviewed
05Multichord Doppler shift measurements of impurity lines show a large, sheared flow during the quiescent period and low, uniform flow profiles during periods of high mode activity, so the stability of the column tracks the flow profile rather than any applied field.Abstract, eighth sentence
Published and peer-reviewed
06Z-pinch plasmas have been produced that are globally stable for over 700 times the growth time theory predicts for the kink mode of a static Z pinch, and the measured sheared axial flow exceeds the theoretical threshold for stability during the quiescent period while falling below it during periods of high mode activity.Abstract, ninth and tenth sentences
Published and peer-reviewed

Read it · abstract

Abstract

The stabilizing effect of a sheared axial flow on the m=1 kink instability in Z pinches has been studied numerically with a linearized ideal magnetohydrodynamic model to reveal that a sheared axial flow stabilizes the kink mode when the shear exceeds a threshold. The sheared flow stabilizing effect is investigated with the ZaP (Z-Pinch) Flow Z-pinch experiment at the University of Washington. An axially flowing Z pinch is generated with a 1 m coaxial accelerator coupled to a pinch assembly chamber. The plasma assembles into a pinch 50 cm long with a radius of approximately 1 cm. An azimuthal array of surface mounted magnetic probes located at the midplane of the pinch measures the fluctuation levels of the azimuthal modes m=1, 2, and 3. After the pinch assembles a quiescent period is found where the mode activity is significantly reduced. Optical images from a fast framing camera and a ruby holographic interferometer indicate a stable, discrete pinch plasma during this time. Multichord Doppler shift measurements of impurity lines show a large, sheared flow during the quiescent period and low, uniform flow profiles during periods of high mode activity. Z-pinch plasmas have been produced that are globally stable for over 700 times the theoretically predicted growth time for the kink mode of a static Z pinch. The plasma has a sheared axial flow that exceeds the theoretical threshold for stability during the quiescent period and is lower than the threshold during periods of high mode activity.

The way in

https://doi.org/10.1063/1.1558294SOURCE NOT REACHED IN FULL. Published as Physics of Plasmas volume 10, issue 5, pages 1683 to 1690, May 2003, copyright AIP Publishing, with no Creative Commons statement on the record. The article is closed at the publisher; on 2026-09-08 Unpaywall and OpenAlex reported no open copy, the Office of Scientific and Technical Information holds no record of it, and the University of Washington ZaP group’s own publication archive, as preserved in the Internet Archive, does not carry a manuscript of it. The abstract below is therefore the publisher’s deposited abstract, verbatim, with the mode numbers set as they are printed. Every claim locator below points to a sentence of that abstract and never into the body of the paper. BACKGROUND READ, NOT CITED AS CLAIMS. The plain-language summary draws on the same team’s companion conference manuscript, EX/P1-19, Flow Shear Stabilization Experiments in the ZaP Flow Z-Pinch, presented at the 2002 International Atomic Energy Agency fusion energy conference and retrieved from the group’s archived publications page; it describes the same machine in the same period, and it is named here as background only — none of its findings are stated as claims of this paper. The work was done in the Aerospace and Energetics Research Program at the University of Washington in Seattle, with D. J. Den Hartog at the University of Wisconsin in Madison. Author initials are left as the published record gives them. Companion sheets: the programme’s 2017 results at /library/stm-610b650dfb, its later statement of the approach at /library/stm-d90424cb8a, and prepulse effects in a fibre Z pinch at /library/stm-06c1a40035.

How to cite it

U. Shumlak, B. A. Nelson, R. P. Golingo, S. L. Jackson, E. A. Crawford, D. J. Den Hartog (2003) Sheared flow stabilization experiments in the ZaP flow Z pinch. doi:10.1063/1.1558294

Where it sits in the curriculum

Lattice confinement fusion Plasmoids, charge clusters and the orbs