In the paper, titled “Inferring morphology and strength of magnetic fields from proton radiographs,” Graziani and his colleagues propose a new theory for analyzing the radiographs of magnetized plasmas. Specifically, they show that in the linear régime, proton radiographic images of magnetized plasmas are projective images of magnetohydrodynamics (MHD) current.
“This fact, which was not previously recognized, lends considerably more diagnostic power to the analysis of such radiographs,” said Graziani. “We are now able to interpret radiographic images not as entangled products of the plasma structure but rather as the direct result of the plasma structure alone.”
In the standard view, structures on radiographs are explained by the formation of caustics, or curved regions of bright light (e.g., the rainbow is a well-known caustic). But the researchers demonstrated that the sharp features in a proton radiograph can be produced by the MHD current in regimes where magnetic field gradients are too weak to produce caustics.
Misidentifying these features can lead to overestimation of magnetic field strengths. The new theory enables scientists to gain new insight into the morphology and the strength of magnetic fields in high energy density laboratory experiments.
For the full paper, see C. Graziani, P. Tzeferacos, D. Q. Lamb, and C. Li, “Inferring morphology and strength of magnetic fields from proton radiographs,” Review of Scientific Instruments, 88, 123507 (2017); https://doi.org/10.1063/1.5013029