Description
The velocity distribution functions (VDFs) of space plasmas typically exhibit non-Maxwellian features owing to the extremely low level of collisionality. Fine velocity-space gradients in the VDFs may play a crucial role in plasma heating and dissipation, as they can inhibit the reversibility of energy exchange between fields and particles once a sufficient degree of phase-space complexity is reached.
A powerful way to quantify this complexity is through the Hermite spectrum of the VDFs. In velocity space, a Hermite cascade—analogous to the turbulent cascade in real space—has been identified in both numerical simulations and observations in the terrestrial magnetosheath.
Here, we present new results on this phenomenon using measurements from Parker Solar Probe and Solar Orbiter, together with gyrokinetic Vlasov simulations of fusion plasmas. These findings advance our understanding of the development of phase-space turbulence in both space and laboratory (fusion) plasma environments.