Experimental investigation of the neutral sheet profile during magnetic reconnection

During magnetic reconnection, a \neutral sheet" current is induced, heat- ing the plasma. The resultant plasma thermal pressure forms a stationary equilibrium with the opposing magnetic elds. The reconnection layer prole holds signicant clues about the physical mechanisms which control reconnec- tion. On the Magnetic Reconnection Experiment (M. Yamada et al. ,P hys. Plasmas 4, 1936 (1997)), a quasi steady-state and axisymmetric neutral sheet prole 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 the reconnecting eld prole ts well with a Harris-type prole (E. G. Harris, Il Nuovo Cimento 23, 115 (1962)), B(x) tanh(x=). This agreement is re- markable since the Harris theory does not take into account reconnection and associated electric elds and dissipation. An explanation for this agreement is presented. The sheet thickness is found to be approximately 0.4 times the ion skin depth, which agrees with a generalized Harris theory incorporating non-isothermal electron and ion temperatures and nite electric eld. The detailed study of additional local features of the reconnection region is also presented.