Field-aligned electric field caused by the decay of force-free magnetic field and particle acceleration

Numerical simulation for the dynamics of a coronal filamentary magnetic loop has been made under the assumption that the field is initially force-free and an electric resistivity suddenly increases at a given moment due to an appearance of ion sound waves, which can be excited due to a high current density if a characteristic radius r ₀ of the magnetic loop is about 3 km or less in a magnetic field B ₀ of 1000 G. During the resistive decay of the magnetic field a strong field-aligned electric field is created and maintained for a sufficient time to acceleratie both electrons and protons to a high energy, which is proportional to B ₀/r ₀ and can be 100 MeV if r ₀ = 10 km and B ₀ = 1000 G. If the coronal magnetic tube is composed of many such filamentary loops, the total number of accelerated electrons is consistent with the observations.