Publication Date:
2016-12-07
Description:
Discrete helical modes have been experimentally observed from implosion to explosion in cylindrical, axially magnetized ultrathin foils ( B z = 0.2 – 2.0 T) using visible self-emission and laser shadowgraphy. The striation angle of the helices, ϕ , was found to increase during the implosion and decrease during the explosion, despite the large azimuthal magnetic field (〉40 T). These helical striations are interpreted as discrete, non-axisymmetric eigenmodes that persist from implosion to explosion, obeying the simple relation ϕ = m/kR , where m , k , and R are the azimuthal mode number, axial wavenumber, and radius, respectively. Experimentally, we found that (a) there is only one, or at the most two, dominant unstable eigenmode, (b) there does not appear to be a sharp threshold on the axial magnetic field for the emergence of the non-axisymmetric helical modes, and (c) higher axial magnetic fields yield higher azimuthal modes.
Print ISSN:
1070-664X
Electronic ISSN:
1089-7674
Topics:
Physics
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