Available Energy of Trapped Electrons and Its Relation to Turbulent Transport

Any collisionless plasma possesses some “available energy” (AE), defined as that part of the thermal energy that can be converted into instabilities and turbulence. Here, we present a calculation of the AE carried by magnetically trapped electrons in a flux tube of collisionless plasma. The AE is compared with nonlinear simulations of the energy flux resulting from collisionless turbulence driven by trapped-electron modes in various magnetic geometries. The numerical calculation of AE is rapid and shows a strong correlation with the simulated energy fluxes, which can be expressed as a power law and understood in terms of a simple model.