Quantitative reconstruction of magnetic fields from proton radiography for colliding magnetized plasmas*

We present techniques for quantitative reconstruction of magnetic fields for magnetic reconnection experiments in laser-produced plasmas, including uncertainty analysis.   Proton radiography uses a source of high-energy protons, which is sent through a plasma experiment, where the protons undergo deflections from the plasma electromagnetic fields, before being imaged on a detector.   Recently, algorithms have been developed which allow inversion of the proton fluence images to obtain the plasma magnetic fields.  We describe application of these techniques using data from the NIF Magnetic Reconnection experiments to obtain magnetic fields with quantitative error bars.  We develop strategies for two key sources of uncertainty: the "zero" proton level or noise floor, which is especially important in the current sheet region; and, long-wavelength non-uniformities in the initial (undeflected) protons which manifest as spurious long-wavelength components of the magnetic fields.