Magnetic Field Line Reconnection Experiment

Abstract

A laboratory experiment on the problem of magnetic field line reconnection in plasmas has been performed. Comprehensive measurements of the magnetic field topologies as well as the plasma dynamics have been performed. The formation of neutral magnetic sheets, tearing, island formation and magnetic turbulence will be shown first. Then, the force density and ion acceleration have been measured. An anomalous ion collision frequency ν* has been derived from these quantities and found to be large, <ν*/f_pi> ≲ 0.5, when turbulence is present. Finally, detailed time-dependent measurements of the total electric field and current density vectors have been made in the large (35 × 85 × 200 cm³), weakly collisional (ν_ei/ω_pe ≃ 10^-4) argon plasma (n₀ ≃ 10¹² cm^-3, T_e = 10 T_i = 6 eV, β ≃ 1). The evolution of a broad (ℓ ≃ 35 cm), thin (Δz ≃ 3 C/ω_pe = 1.5 cm) neutral current sheet is seen to coincide with an increase in the calculated resistivity. The resistivity is found to be spatially inhomogeneous with average values exceeding the classical resistivity by one order of magnitude and locally by two orders.