Escape of O+ Through the Distant Tail Plasma Sheet

During the early orbit phase of the STEREO mission, in February, 2007, the STEREO-B spacecraft went down the deep magnetotail, and encountered the magnetosheath, plasma sheet and plasma sheet boundary layer from about 200 Re to 300 Re downtail, before finally exiting to the solar wind. This time period was during solar minimum, and there was no storm activity during this month. We have used the ion composition data from the PLASTIC instrument to determine how much ionospheric O+ is in the deep tail plasma sheet, and to calculate the loss rate through this path. Surprisingly, we find that during this solar and geomagnetically quiet time, O+ is a constant feature of the deep magnetotail. We find that the O+ density is about 15% of the density in the near-earth plasma sheet for similar conditions. The tailward flux of the O+ is similar to the flux of O+ beams that have been observed in the lobe/mantle region of the deep tail. The observations provide a consistent picture that some O+ is transported into the distant tail in the lobe/mantle region, and then enters the plasma sheet tailward of the distant neutral line. The total outflow of the O+ down the plasma sheet is a rate of 1.1x1024 ions/s, which is 10% of the total outflow rate of 1x 1025 ions/s, and of the same order as the estimated loss from dayside transport.