Electron and ion heating, acceleration and energy partition during magnetic reconnection

Magnetic reconnection converts energy into high-speed flows, thermal and energetic particles in a broad range of systems both in the heliosphere and the broader universe. The most detailed measurements are within the heliosphere, which therefore acts as an effective laboratory for many issues related to reconnection. While the mechanisms for fast reconnection are now fairly well understood, the energy conversion mechanisms and the partitioning between species are active topics. In solar flares the energy released is roughly equally partitioned between the thermal particles and the energetic components. In the magnetosphere and the laboratory thermal ions carry the bulk of the released energy and the scaling of the temperature increments of both species with the available free energy per particle $m_ic_{Aup}^2$ has recently been established. Models and simulations are advancing the physics in both relativistic and non-relativistic reconnection. Most of the energy conversion takes place in the exhaust where newly reconnected field lines release their tension and during the merger of magnetic islands. The three basic mechanisms for energy conversions are Fermi reflection, parallel electric fields and betatron acceleration. The former two mechanisms are typically the most important with Fermi reflection dominating the energy gain of the most energetic particles in both electron-ion and pair plasma. The production of particles with energy greatly exceeding $m_ic_{Aup}^2$ requires the interaction with multiple magnetic islands. The dominant energy gain is parallel to the local magnetic field and as a consequence significant anisotropy develops, which is likely to impact synchrotron signatures. Why the powerlaw distributions that are typically seen in nature are produced remains an open question. Basic physics concepts will be emphasized.

Speaker: Jim Drake, Univ. of Maryland