During magnetic reconnection, a "neutral sheet" current is induced, heating
the plasma. The resultant plasma thermal pressure forms a stationary equil
ibrium with the opposing magnetic fields. The reconnection layer profile ho
lds significant clues about the physical mechanisms which control reconnect
ion. In the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasm
as 4, 1936 (1997)], a quasi steady-state and axisymmetric neutral sheet pro
file has been measured precisely using a magnetic probe array with spatial
resolution equal to one quarter of the ion gyro-radius. It was found that t
he reconnecting field profile fits well with a Harris-type profile [E. G. H
arris, Il Nuovo Cimento 23, 115 (1962)], B(x) similar to tanh(x/delta). Thi
s agreement is remarkable since the Harris theory does not take into accoun
t reconnection and associated electric fields and dissipation. An explanati
on for this agreement is presented. The sheet thickness delta is found to b
e similar to 0.4 times the ion skin depth, which agrees with a generalized
Harris theory incorporating nonisothermal electron and ion temperatures and
finite electric field. The detailed study of additional local features of
the reconnection region is also presented. (C) 2000 American Institute of P
hysics. [S1070-664X(00)95505-8].