Experimental investigation of thermal plasma formation from thick aluminum surfaces by pulsed multimegagauss magnetic field

Awe, T. J.; Bauer, B. S.; Fuelling, S.; Lindemuth, I. R.; Siemon, R. E.
October 2010
Physics of Plasmas;Oct2010, Vol. 17 Issue 10, p102507
Academic Journal
The thermal ionization of a thick metal surface by pulsed multimegagauss magnetic field has been examined experimentally. Thick 6061-alloy Al rods with initial radii (R0) from 1.00 to 0.25 mm, larger than the magnetic field skin depth, are pulsed to 1.0 MA peak current in 100 ns. Surface fields (Bs) rise at 30-80 MG/μs and reach 1.5 and 4 MG, respectively. For this range of parameters, plasma forms at a threshold level of Bs=2.2 MG. Novel load hardware ensures that plasma formation is thermal, by Ohmic or compression heating. Surface-plasma formation is conclusively indicated through radiometry, extreme ultraviolet spectroscopy, and gated imaging. When R0=0.50 mm rods reach peak current, Bs=3 MG, the surface temperature is 20 eV, and Al3+ and Al4+ spectra and surface instabilities are observed. In contrast, R0=1.00 mm rod surfaces [Bs(t)<2.2 MG] reach only 0.7 eV and remain extremely smooth, indicating that no plasma forms.


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