Unfortunately , velocity - space cascades have traditionally been difficult to diagnose , both in satellite data and in numerical simulations . Although several 3D simulations of kinetic / gyrokinetic turbulence exist ( e.g. , Howes et al . 2008Howes et al . , 2011Servidio et al . 2015;Told et al . 2015;Wan et al . 2016;Groselj et al . 2017;Franci et al . 2018;Arzamasskiy et al . 2018 ) , thus far the velocity - space cascade produced by nonlinear phase mixing has been directly diagnosed only in 2D simulations of gyrokinetic electrostatic turbulence ( Tatsuno et al . 2009(Tatsuno et al . , 2012 , with little other indirect evidence ( Bañón Navarro et al . 2011;Cerri et al . 2014 ) .