SOLAR-WIND DOUBLE ION-BEAMS AND THE HELIOSPHERIC CURRENT SHEET

Double ion beams are often observed in the solar wind, but little work has been done in relating these beams to structures within the solar wind. Double ion beams are observed as beams of a given ion species an d charge state occurring at two different energies. We use the three-d imensional ion plasma instrument on board the Ulysses spacecraft to lo ok for evidence of such beams associated with the heliospheric current sheet. In a subset chosen independently of plasma parameters consisti ng of 8 of over 47 crossings of the current sheet made during the in-e cliptic phase of the Ulysses mission we find that these double ion bea ms are always present on either side of the current sheet. The double beams are present in both the proton and helium species. The secondary beam typically has a higher helium abundance, which suggests that the se beams are formed in the helium-rich corona rather than in interplan etary space. The double beams are not present in the interior of the c urrent sheet. Neither collisions nor effects of plasma beta can accoun t for the disappearance of the double beams inside the current sheet i ri all eight cases. We postulate that these beams are formed by reconn ection occurring near the Sun in the boundary region between the open field lines of the coronal holes and the closed field line region of t he heliospheric current sheet. Such a scenario would be consistent wit h previous X ray measurements which suggest that reconnection is occur ring in this region.