Ion temperature anisotropy measurements using the Solar Probe Cup on Parker Solar Probe

Ion temperature anisotropies are fundamental properties of plasma velocity distribution functions indicative of various unstable modes which often lead to energy dissipation through wave generation. Typically this quantity is directly measured using particle detectors spanning multiple look directions relative to the magnetic field. Using the Solar Probe Cup (SPC) on board Parker Solar Probe, we are able to infer the temperature anisotropy of the bulk solar wind plasma by examining the change in plasma flow angle across each scan through particle energy/charge. This gives us the possibility of measuring ion temperature anisotropy on the order of the instrument operation cadence, which is typically greater than 1 sample per second during each Solar encounter. Additionally, as the SPC looks directly at the Sun, we are able to measure the anisotropy at times when other instruments are unable to sample the full particle distribution due to limitations from look directions and shielding. We examine the behavior of this temperature anisotropy measurement relative to observed wave phenomena and other plasma parameters. To our knowledge, this use of SPC data is the first derivation of temperature anisotropy measurements using this method from a Faraday Cup instrument.