Structure of Cusp Diamagnetic Cavities

While in the cusp region, POLAR regularly observes large (up to 6 RE) cavities characterized by depressed magnetic field and increased plasma pressure. The frequent occurance and apparent stability of these structures implies a pressure balance between the plasma inside and the field outside. We investigate this balance, using pressures derived from the HYDRA and MFE instruments and composition information from CAMMICE MICS, for multiple crossings of the cusp. Our results suggest that small-scale physics drives the structure of these regions.