  Current sheet is believed to be the region of energy dissipation via magnetic
reconnection in solar flares. However, its properties, for example, the dynamic
process, have not been fully understood. Here we report a current sheet in a
solar flare (SOL2017-09-10T16:06) that was clearly observed by the Atmospheric
Imaging Assembly on board the Solar Dynamics Observatory as well as the EUV
Imaging Spectrometer on Hinode. The high-resolution imaging and spectroscopic
observations show that the current sheet is mainly visible in high temperature
(>10 MK) passbands, particularly in the Fe XXIV 192.03 line with a formation
temperature of ~18 MK. The hot Fe XXIV 192.03 line exhibits very large
nonthermal velocities up to 200 km/s in the current sheet, suggesting that
turbulent motions exist there. The largest turbulent velocity occurs at the
edge of the current sheet, with some offset with the strongest line intensity.
At the central part of the current sheet, the turbulent velocity is negatively
correlated with the line intensity. From the line emission and turbulent
features we obtain a thickness in the range of 7--11 Mm for the current sheet.
These results suggest that the current sheet has internal fine and dynamic
structures that may help the magnetic reconnection within it proceeds
efficiently.
