Diagnosing coronal magnetic fields with MUSER observations

Understanding how the magnetic field is structured in the solar corona is a major task to solar physics as the magnetic field plays a major role in controlling all physical processes and observed phenomena in the solar corona. Several ways are normally employed to investigate coronal fields. For example, the EUV/UV and/or SXR images are used to diagnose coronal magnetic structures. The EUV/UV and/or SXR loop or thread-like structures are believed to resemble the coronal magnetic field. At present reliable magnetic field measurements are mainly confined to the photosphere and extrapolation from observed boundary data upwards is still a challenging problem. Direct measurement of the coronal magnetic field is possible in IR but difficult to make and to interpret. With assumptions on radiation mechanisms and propagations, radio techniques can be applied to diagnose coronal fields but with uncertainties due to free parameters involved without sufficient observational constraints previously. So wideband radio image-spectroscopic observations will provide new opportunities to improve the coronal magnetic field diagnoses. Mingantu Spectral Radioheliograph (MUSER) is a radio synthesis imaging telescope, dedicated to observe the Sun, operating on multiple frequencies in dm to cm range, which corresponds to the regime where primary energy release processes, particle accelerations, as well as their propagation can be addressed. The ability of MUSER to get images and measure Stokes I and V parameters simultaneously at many frequencies in a wide band is of fundamental importance. It allows us to approach/solve measuring the strength, geometry and dynamics of the magnetic field at coronal heights. Here we consider some of the recently developed radio physics methods to be used for solving the problems.