Center for Magnetic Self Organization
in Laboratory and Astrophysical Plasmas
Energetic ion creation during magnetic reconnection in the RFP
Particle heating is an important process related to magnetic reconnection. A large part of a systemís magnetic energy can be transferred to thermal energy during the reconnection process. In the reversed field pinch, the ions are well established to be heated in this way. Past measurements of the ion temperature have focused on the bulk, thermal portion of the ion distribution. New measurements reported here using a neutral particle diagnostic reveal that there is, in addition, a significant population of ions that form an energetic tail, as shown in the figure below. Ions in the plasma undergo charge-exchange with background neutrals and are allowed to cross the magnetic field confining the plasma. The escaping neutral flux detected by the particle analyzer is energy-resolved and therefore reflects the ion distribution in the plasma. There is an excess of neutrals (i.e., ions) at high energy relative to the thermal Maxwellian bulk. This tail is enhanced during the magnetic reconnection process, and is well fit to a power-law energy dependence. Such power-law particle distributions are commonly observed in astrophysical plasmas, and represent an important clue as to the origin of the ion energization process.
The neutral particle flux escaping the MST plasma, before and after a magnetic reconnection event (of short duration). The blue curves represent the bulk thermal ions with Ti ~ 300 eV, well described as a Maxwellian (straight lines). The red curves characterize the tail ions, well described by a power-law energy dependence.