Magnetic field generation in shock waves

Abstract

Laser produced plasma jets interacting with a background plasma have been used to study magnetic field generation in shock waves. The equation which governs the changes in the magnetic field as a function of time is, ∂B↘/∂t = ∇×(V↘e×B↘)+1/μ0σ ∇2B↘ +k/ene ∇Te×∇ne The first two terms on the right hand side are the convection and diffusion terms. The third term represents the source term for magnetic field generation due to non‐parallel temperature and density gradients. Shock heating provides axial electron temperature and density gradients. For large Mach numbers the axial shock compression ratio of the density approaches a limiting value of 4 while the temperature ratio can increase far above 4. This combination of non‐parallel axial temperature and radial density gradients generates a magnetic field in the azimuthal direction. Simulations confirm the experimental observation that magnetic fields are generated when a supersonic plasma jet interacts with a background plasma. This mechanism for magnetic field generation can occur in a field free region where B↘=0, in contrast to the dynamo mechanism which requires an initial seed magnetic field. It may be assumed that this mechanism of magnetic field generation is also of importance under astrophysical conditions.