Evolution of alpha particle content at flux rope boundaries as seen by Solar Orbiter

<p>The solar wind is highly structured and consists of bundles of flux ropes. Their boundaries can be identified as sharp changes of the magnetic field magnitude and/or direction that are frequently accompanied with changes of plasma parameters like velocity, density and ion composition. An analysis of observations showed that flux rope diameters can range from thousands of kilometers to tenth of AU. Whereas the small ropes can be hardly distinguished from structures produced by nonlinear interaction of plasma waves, large ropes like ICMEs or MCs attract attention of scientific community for years. The velocity within these structures can significantly differ from that in the ambient wind and thus they can drive interplanetary shocks followed by highly fluctuating sheaths. The contribution is based on Solar Orbiter PAS ion spectrometer observations of one MC like structure. The good radial alignment with other spacecraft operating in the interplanetary space allows us comparison of their observations. The alpha abundance variations are usually attributed to crossings of the flux rope boundaries but we argue that the processes like the mirroring at temporary created magnetic field enhancements can lead to changes of the alpha particle relative content within a single flux rope. We show that the sheath fluctuations are complex but a careful analysis of relative alpha particle abundance can help to resolve the original flux rope structure that is masked by intrinsic sheath fluctuations.</p>