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

• Published in: Physics of plasmas 2010-10, Vol.17 (10), p.102507-102507-11
• Main Authors: Awe, T. J., Bauer, B. S., Fuelling, S., Lindemuth, I. R., Siemon, R. E.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ALLOYS; ALUMINIUM ALLOYS; ELECTRIC HEATING; HEATING; IONIZATION; JOULE HEATING; MAGNETIC FIELDS; PLASMA HEATING; SURFACES
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.3491335

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 ( R 0 ) 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 ( B s ) rise at 30 − 80   MG / μ s and reach 1.5 and 4 MG, respectively. For this range of parameters, plasma forms at a threshold level of B s = 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 R 0 = 0.50   mm rods reach peak current, B s = 3   MG , the surface temperature is 20 eV, and Al 3 + and Al 4 + spectra and surface instabilities are observed. In contrast, R 0 = 1.00   mm rod surfaces [ B s ( t ) < 2.2   MG ] reach only 0.7 eV and remain extremely smooth, indicating that no plasma forms.