Energy‐dispersed H+ structures observed by Equator‐S in the sub‐keV range in the dawn sector of the ring current region were used to perform the remote sensing of cold ions in the near‐earth plasma sheet. A time history of the source distribution function in the nightside plasma sheet was reconstructed by using the phase space mapping method under a time‐dependent convection electric field model. We obtained the following major conclusions: (1) A cold H+ component (∼10 eV) exists in the near‐earth plasma sheet. (2) The cold component is readily distinguished from the main component of the plasma sheet (>∼a few keV). (3) The cold component is distributed over a relatively wide area in MLT. (4) Energy‐dispersed H+ structures in the inner magnetosphere results from temporal variation of the cold component. Our scheme will be applicable for investigating long‐term plasma processes acting on the cold component whose behavior is largely unknown.
