Experimental Observation of a Field-Aligned Ion Beam Produced by Magnetic Reconnection of Two Flux Ropes on the LArge Plasma Device

Magnetic reconnection is the process in which magnetic energy is converted into heat or electric fields that can energize the plasma and/or accelerate particles. This is typically observed in space such as in the solar corona, as well as in various laboratory experiments and plasma simulations. In a study of two flux ropes (L=11 m, d=7.6 cm) on the LArge Plasma Device (LAPD), the energization of ions due to magnetic reconnection that is triggered by the collision of the two flux ropes is explored. A retarding field energy analyzer was constructed to measure the local ion energy distribution function of the plasma and a 9 to 15 eV sub-Alfvénic ion beam moving in the direction of the background magnetic field was observed. To the authors' knowledge, this is the first known observation of an ion beam that is field-aligned to the guide field. The beam ions do not appear to be heated and are accelerated in the direction of the induced electric fields (-dA_z/dt). In addition, the energy released from magnetic field annihilation appears to be sufficient to account for the increase in the energy of the ions. Evidence suggests that the presence of the beam is correlated with the oscillation of the ropes and could cause ion acoustic waves that propagate along the magnetic field.