Magnetic field calculation from the Thomson scattering spectra in Weibel unstable counter-streaming plasmas*

Thomson Scattering (TS) is a powerful diagnostic for evaluating the properties of high-energy-density plasmas. We analyze TS cross-sections and dynamical form factors from electron density fluctuations and from distribution functions in particle-in-cell (PIC) simulations of Weibel unstable counter steaming plasma relevant to astrophysical collionsionless shocks. These form factors are compared with analytical theory results and experimental measurements. 

 

We demonstrate for the first time the capability to calculate local magnetic field gradients from beam modes in TS spectra from quasi stationary plasma corresponding to a saturated state of the Weibel instability.  This method is compared to the magnetic fields present in PIC simulations.  We also show that the temporal evolution of the TS spectra can provide some information about the non-linear stage of the instability.  These techniques are applied to TS Spectra from recent experiments at the Omega facility to estimate the magnetic field strength generated.