R. Lionello et al., CURRENT SHEET FORMATION DUE TO NONLINEAR KINK MODES IN PERIODIC AND LINE-TIED CONFIGURATIONS, Physics of plasmas, 5(10), 1998, pp. 3722-3731
The full magnetohydrodynamic evolution of kink instabilities in cylind
rical geometry is computed. The equilibria investigated serve as gener
ic models of coronal loops. The effects of both periodic and line-tyin
g boundary conditions at the axial ends of the cylinder are compared a
nd contrasted. The net axial current, which is distributed internally
to the loop, can be varied from case to case. It is found that one eff
ect of the line-tying boundary condition is that the minimum length fo
r the onset of a kink instability is increased. For line-tied loops, r
esonant surfaces do not exist, though linear analysis shows that there
may or may not occur quasi-resonant regions, i.e., regions of strong
gradients, which, however, are confined to the loop apex, far from the
line-tied boundaries. When such a region is present for the linear mo
de, the formation and nonlinear development of current layers is confi
ned to the central region of the loop. In a case where no such regions
exist for the linear mode (corresponding to k . B not equal 0 in the
periodic cylinder!, current concentrations appear two thirds of the wa
y from the center of the loop. This effect disappears in the axially p
eriodic case. The consequences of these results for solar physics are
discussed. (C) 1998 American Institute of Physics. [S1070-664X(98)0101
0-6].