PARTICLE ACCELERATION IN RECONNECTING CURRENT SHEETS WITH A NONZERO MAGNETIC-FIELD

Motion of charged particles in a reconnecting current sheet (RCS) is c onsidered, taking into account not only the electric field inside it b ut also all three components of the magnetic held. A new solution for the particle trajectory is found for the case of a large longitudinal magnetic field. It allows one to find the ''critical'' value of the he ld, beyond which the particle motion in the sheet becomes adiabatic. T he longitudinal component in RCSs in the solar atmosphere is likely to exceed this value (typically 0.1 of the main reconnecting field for e lectrons). The longitudinal field tends to counteract the effect of th e transverse magnetic field that serves to rapidly eject the particles out of the sheet. Hence, a longitudinal component on the order of the reconnecting component is necessary to explain the electron accelerat ion in RCSs up to 10-100 keV during the impulsive phase of solar flare s. The electron acceleration length turns out to be 5 orders of magnit ude smaller than the RCS length, placing strong requirements on the el ectric field necessary to accelerate the particles. This indicates tha t it is necessary to modify the simplistic runaway acceleration models , which ignore the magnetic field altogether. Depending upon the magne tic field structure in the RCS, the energy can reside mainly in electr ons or protons. Thus, the model gives a unified description for differ ent regimes of particle acceleration in flares.