Optimal geometry for neutral‐beam‐based optical diagnostics in tokamaks

Spatial resolution is an important issue for neutral-beam-based optical diagnostics in tokamak plasmas, such as charge-exchange recombination spectroscopy (measuring T{sub i} and v{sub {phi}}) and motional Stark effect (measuring B{sub p}). The key geometrical constraint is that the optical sightlines of these diagnostics must be as nearly tangent as possible to magnetic surfaces at the point where they cross the path of the neutral beam. This minimizes the effect of the width of the neutral beam on the spatial resolution of the diagnostic in the direction perpendicular to the flux surfaces

Synchrotron Radiation From Radiatively Inefficient Accretion Flow Simulations: Applications to Sgr A*

We calculate synchrotron radiation in three-dimensional pseudo-Newtonian magnetohydrodynamic simulations of radiatively inefficient accretion flows. We show that the emission is highly variable at optically thin frequencies, with order of magnitude variability on time-scales as short as the orbital period near the last stable orbit; this emission is linearly polarized at the 20-50 % level due to the coherent toroidal magnetic field in the flow. At optically thick frequencies, both the variability amplitude and polarization fraction decrease significantly with decreasing photon frequency. We argue that these results are broadly consistent with the observed properties of Sgr A* at the Galactic Center, including the rapid infrared flaring.Comment: Accepted for publication in Ap