We investigate properties of the ion-scale spectral break of solar wind turbulence by means of two-dimensional high-resolution hybrid particle-in-cell simulations .
We impose an initial ambient magnetic field perpendicular to the simulation box and add a spectrum of in-plane , large-scale , magnetic and kinetic fluctuations .
We perform a set of simulations with different values of the plasma \beta , distributed over three orders of magnitude , from 0.01 to 10 .
In all the cases , once turbulence is fully developed , we observe a power-law spectrum of the fluctuating magnetic field on large scales ( in the inertial range ) with a spectral index close to -5 / 3 , while in the sub-ion range we observe another power-law spectrum with a spectral index systematically varying with \beta ( from around -3.6 for small values to around -2.9 for large ones ) .
The two ranges are separated by a spectral break around ion scales .
The length scale at which this transition occurs is found to be proportional to the ion inertial length , d _ { i } , for \beta \ll 1 and to the ion gyroradius , \rho _ { i } = d _ { i } \sqrt { \beta } , for \beta \gg 1 , i.e. , to the larger between the two scales in both the extreme regimes .
For intermediate cases , i.e. , \beta \sim 1 , a combination of the two scales is involved .
We infer an empiric relation for the dependency of the spectral break on \beta that provides a good fit over the whole range of values .
We compare our results with in situ observations in the solar wind and suggest possible explanations for such a behavior .