Princeton Plasma Physics Laboratory (PPPL) Colloquium

The NASA Parker Solar Probe (PSP) mission was launched in 2018 and has made 20 orbits of the Sun with perihelion altitudes down to 10.3 solar radii. After a Venus Gravity Assist in November of this year, perihelion will reach 8.8 solar radii above the photosphere. An increasingly plausible picture is emerging of where the solar wind originates, how it is initially energized, and the plasma physics of the extended wind heating process. In this scenario, the wind originates by magnetic reconnection at intense bundles of field energy associated with the supergranulation convection cells. The emerging wind generates Alfven waves, by the reconnection process, shearing instabilities, or phase speed gradients. These Alfven waves grow to large amplitude dB/B~1 by a combination of plasma expansion and conservation of wave action. The large nonlinear Alfven waves generate small scale turbulence that results in plasma (ion cyclotron) heating, which provides the thermal energy to counteract the cooling of expansion. I will review some of the key PSP results that underpin this scenario and I will show a surprising result suggesting that the radial evolution of these nonlinear Alfven waves generates significant magnetic field in a dynamo-like process.