Title: Inferring morphology and strength of magnetic fields from proton radiographs

Abstract

Proton radiography is an important diagnostic method for laser plasma experiments and is particularly important in the analysis of magnetized plasmas. The theory of radiographic image analysis has heretofore only permitted somewhat limited analysis of the radiographs of such plasmas. We furnish here a theory that remedies this deficiency. We show that to linear order in magnetic field gradients, proton radiographs are projection images of the MHD current along the proton trajectories. We demonstrate that in the linear regime (i.e., the small image contrast regime), the full structure of the projected perpendicular magnetic field can be reconstructed by solving a steady-state inhomogeneous 2-dimensional diffusion equation sourced by the radiograph fluence contrast data. Here, we explore the validity of the scheme with increasing image contrast, as well as limitations of the inversion method due to the Poisson noise, discretization errors, radiograph edge effects, and obstruction by laser target structures. We also provide a separate analysis that is suited to the inference of isotropic-homogeneous magnetic turbulence spectra. Finally, we discuss extension of these results to the nonlinear regime (i.e., the order unity image contrast regime).

Authors:

Graziani, Carlo  ^[1];

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Tzeferacos, Petros ^[1]; Lamb, Donald Q. ^[1]; Li, Chikang ^[2]

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+ Show Author Affiliations

1. Univ. of Chicago, IL (United States). Flash Center for Computational Science, Dept. of Astronomy and Astrophysics
2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center

Publication Date:

2017-12-20

Research Org.:

Univ. of Chicago, IL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Fusion Energy Sciences (FES)

OSTI Identifier:

1524603

Alternate Identifier(s):

OSTI ID: 1414330

Grant/Contract Number:  

SC0016566; AC02-06CH11357; B523820; PHY-0903997; PHY-1619573

Resource Type:

Accepted Manuscript

Journal Name:

Review of Scientific Instruments

Additional Journal Information:

Journal Volume: 88; Journal Issue: 12; Journal ID: ISSN 0034-6748

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY