On 2017 September 10, a major eruption on the west solar limb produced a class X-8.2 flare and a superfast coronal mass ejection (CME). During the eruptive process, the geometric topology of the erupting magnetic configuration presented a clear flare-current sheet (CS)-CME structure. Analysing the images and spectral data from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), the Interface Region Imaging Spectrograph (IRIS) and Hinode/EUV Imaging Spectrometer (EIS), we studied the supra-arcade fan (SAF) region between the bottom of the CS and the top of the flare loops in the south part of the erupting configuration. Our results indicated that the SAF contained hot plasma of temperature up to 107 K and mean electron density 3.5 × 10^9 {cm^{-3}} and the fast variation component (FVC) of the SAF light curve shown by the IRIS slit-jaw images (SJI) displayed a quasi-periodic oscillating feature with a period of 76.8 s. We utilized the ATHENA code to simulate the detailed evolutionary features of the magnetic structure of a typical two-ribbon flare. The numerical experiments duplicate the observational features in many respects, including the spatial distribution and evolution in the structure of the plasma and magnetic field, the turbulence and the termination shock (TS) in the SAF. Our results suggest that the SAF is a high-temperature structure that possibly contains the TS.
