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We investigate the nature of magnetic turbulent fluctuations, around ioncharacteristic scales, in a fast solar wind stream, by using {\it Cluster}data. Contrarily to slow solar wind, where both Alfv\'enic ($\delta b_{\perp}\gg \delta b_{\parallel}$) and compressive ($\delta b_{\parallel} \gg \deltab_{\perp}$) coherent structures are observed \cite[]{per16}, the turbulentcascade of fast solar wind is dominated by Alfv\'enic structures, namelyAlfv\'en vortices, with small and/or finite compressive part, with the presencealso of several current sheets aligned with the local magnetic field. Severalexamples of vortex chains are also recognized. Although an increase of magneticcompressibility around ion scales is observed also for fast solar wind, nostrongly compressive structures are found, meaning that the nature of the slowand fast winds is intrinsically different. Multi-spacecraft analysis applied tothis interval of fast wind indicate that the coherent structures are almostconvected by the flow and aligned with the local magnetic field, i.e. theirnormal is perpendicular to {\bf B}, that is consistent with a two dimensionalturbulence picture. Understanding intermittency and the related generation ofcoherent structures could provide a key insight into the nonlinear energytransfer and dissipation processes in magnetized and collisionless plasmas.

Coherent structures at ion scales in fast solar wind: {\it Cluster} observations