Release of helium from closed-field regions of the sun

Using a numerical model that extends from the chromosphere into the supersonic solar wind, we study the dynamics of previously closed coronal flux tubes that open, allowing plasma to be expelled from the corona. In particular, we study whether the opening of flux tubes may provide a source of helium-rich material for the solar wind. We use higher order moment fluid equations to describe the plasma, which consists of hydrogen (neutral and protons), helium (neutral, singly ionized, and α -particles), and electrons. The helium abundance decreases rapidly with altitude in a closed flux tube, caused by the collisional coupling between α-particles and protons leading to a small α-particle scale height. When the flux tube is rapidly opened, protons escape from the Sun immediately. The coronal α-particles leave the corona only much later, 10-20 hr after the protons, when the collisional coupling to protons has eased, allowing their temperature to become sufficiently high for them to escape.