Separating the contributions of electric and magnetic fields in deflecting the probes in proton radiography with multiple proton energies

In proton radiography,degeneracy of electric and magnetic fields in deflecting the probe protons can prevent full interpretation of proton flux perturbations in the detection plane.In this paper,theoretical analyses and numerical simulations suggest that the contributions of the electric and magnetic fields can be separately obtained by analyzing the difference between the flux distributions of two discriminated proton energies in a single shot of proton radiography.To eliminate the influence of field evolution on the separation,a strategy is proposed in which slow field evolution is assumed or an approximate estimate of field growth is made.This could help achieve a clearer understanding of the radiographic process and allow further quantitative analysis.

Kinetic study of transverse electron-scale interface instability in relativistic shear flows

Interfacial magnetic field structures induced by transverse electron-scale shear instability(mushroom instability)are found to be strongly associated with electron and ion dynamics,which in turn will influence the development of the instability itself.We find that high-frequency electron oscillations are excited normal to the shear interface.Also,on a larger time scale,the bulk of the ions are gradually separated under the influence of local magnetic fields,eventually reaching an equilibrium related to the initial shear conditions.Wepresent a theoretical model of this behavior.Such separation on the scale of the electron skin depth will prevent different ions from mixing and will thereafter restrain the growth of higher-order instabilities.We also analyze the role of electron thermal motion in the generation of the magnetic field,and we find an increase in the instability growth rate with increasing plasma temperature.These results have potential for providing a more realistic description of relativistic plasma flows.

A demonstration of extracting the strength and wavelength of the magnetic field generated by the Weibel instability from proton radiography

The Weibel instability and the induced magnetic field are of great importance for both astrophysics and inertial confinement fusion.Because of the stochasticity of this magnetic field,its main wavelength and mean strength,which are key characteristics of the Weibel instability,are still unobtainable experimentally.In this paper,a theoretical model based on the autocorrelation tensor shows that in proton radiography of the Weibel-instability-induced magnetic field,the proton flux density on the detection plane can be related to the energy spectrum of the magnetic field.It allows us to extract the main wavelength and mean strength of the two-dimensionally isotropic and stochastic magnetic field directly from proton radiography for the first time.Numerical calculations are conducted to verify our theory and show good consistency between pre-set values and the results extracted from proton radiography.