Physics
Scientific paper
Apr 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aps..apr.d1038p&link_type=abstract
American Physical Society, APS April Meeting, April 22-26, 2006, abstract #D1.038
Physics
Scientific paper
Experimental observation of magnetorotational instability (MRI) in high temperature lab plasmas is difficult because the strong magnetic field suppresses the MRI. However, in the vicinity of rational surfaces with k= 0 magnetic perturbations are small, allowing for excitation of the modes similar to MRI. They are driven by the flow shear and stabilized by the magnetic shear that determines strong radial localization of perturbations. We consider a plasma cylinder with helical magnetic field and two different flows: pure axial flow uz(r) and pure poloidal (rotational) flow uθ(r)= rφ(r). We reduce marginal stability criteria [1] for the case of the large flow gradient and find that uθ(r) can drive both a resonant compressible mode, if r^2 |dφ/dr| ˜cs, and an MRI-like mode, if r^2 |dφ/dr| ˜vA, while axial flow can generate only compressible instability, when r |duz/dr| ˜cs (the unstable band is very narrow). These results suggest that the instability from axial flow can possibly be observed in the Madison Symmetric Torus (MST) experiment if flow is driven (for example by biased electrodes). We also report results on resistive analog of this instability that becomes important if the flow is ideally stable. [1] A. Bondeson, R. Iacono, and A. Bhattacharjee, Phys. Fluids, 30 (7), 2167 (1987).
Mirnov Vladimir V.
Pariev Vladimir I.
Prager Stewart C.
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