Electron Weibel instability-generated magnetic fields in laser-produced plasmas*

The Biermann battery is understood to be the mechanism for generating seed magnetic fields in interstellar plasma, however it is hard to explain how these fields could have been amplified to observed levels [RM Kulsrud & EG Zweibel RPP 71 (2008)]. The Weibel instability is another candidate for field generation and amplification. Predicted by PIC simulations to exist in plasmas with sufficiently strong thermal anisotropy, the Weibel instability can generate magnetic fields which exceed the amplitude of the Biermann fields [Schoeffler et al. PRL 112 (2014)]. Relevant plasmas can be produced in the laboratory with inertial confinement fusion lasers: these ~ns-duration, ~kJ-energy pulses set up strong density and temperature gradients which support the Biermann battery (as has been established by prior work) and a thermal anisotropy which supports the electron Weibel instability. This work reports on data from the OMEGA laser spanning a range of densities and temperatures that is used to to explore the dynamics of the observed magnetic field generating filamentary instability, whose properties are consistent with PIC-predicted properties of the electron Weibel instability.