Historical research guide · 1077 · 2003
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
In one minute
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.
Connection
Chapter 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.
From the source
A 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
The 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
An 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
Two 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
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, so the stability of the column tracks the flow profile rather than any applied field.Abstract, eighth sentence
Z-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
The way in
https://doi.org/10.1063/1.1558294How 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