Abstract
The Weibel instability is caused by anisotropy in the velocity distribution. In the collisionless spherical corona of a laser fusion target, anisotropy in electron velocity space is naturally produced by a localized source because angular momentum, l=mvr, is conserved and the perpendicular energy, E=l2/2mr2, decreases at radii large compared to the source radius. This occurs even if the source is locally isotropic (e.g., inverse bremsstrahlung around the critical density). Linear growth rates are computed for the Weibel instability with a model distribution that includes the aforementioned effects as well as diffusion in angular momentum and energy loss by hydrodynamic expansion.