Effects of the non-uniform initial environment and the guide field on the plasmoid instability

Effects of non-uniform initial mass density and temperature on the plasmoid instability are studied via 2.5-dimensional resistive magnetohydrodynamic (MHD) simulations. Our results indicate that the development of the plasmoid instability is apparently prevented when the initial plasma density at the center of the current sheet is higher than that in the upstream region. As a result, the higher the plasma density at the center and the lower the plasma beta in the upstream region, the higher the critical Lundquist number needed for triggering secondary instabilities. When beta = 0.2, the critical Lundquist number is higher than 10(4). For the same Lundquist number, the magnetic reconnection rate is lower for the lower plasma beta case. Oppositely, when the initial mass density is uniform and the Lundquist number is low, the magnetic reconnection rate turns out to be higher for the lower plasma beta case. For the high Lundquist number case (>10(4)) with uniform initial mass density, the magnetic reconnection is not affected by the initial plasma beta and the temperature distribution. Our results indicate that the guide field has a limited impact on the plasmoid instability in resistive MHD. (C) 2013 AIP Publishing LLC.