Turbulence in magnetized plasmas is supposed to cascade. Energy injected at large scales transfers through an inertial range — a power-law scaling region — before dissipating at small scales. The inertial range is the signature of developed turbulence, the evidence that nonlinear interactions are redistributing energy across wavenumbers in a self-similar way. Kolmogorov's picture, adapted to magnetohydrodynamics.

In broadband kinetic Alfvén wave turbulence under plasma sheet boundary layer conditions, the inertial range is absent. Energy transitions directly from injection to dissipation without the intermediate scaling region.

The mechanism is ponderomotive coupling. The kinetic Alfvén waves create radiation pressure gradients that expel plasma from regions of intense wave activity, forming density cavitations — holes in the plasma density. These cavitations develop within the first few wave periods and organize into spatially intermittent, filamentary structures. The filaments concentrate the energy dissipation into localized channels rather than distributing it across a spectrum of interacting modes.

The result is that the spectral character of the turbulence is governed by moderate-Reynolds-number constraints rather than by the wave physics alone. The cascade doesn't fail because the waves are unusual. It fails because the ponderomotive feedback reorganizes the spatial structure before the cascade has time to develop. The turbulence self-organizes into coherent structures that short-circuit the energy transfer pathway.

This matters for interpreting spacecraft observations of plasma turbulence. Power-law spectra in magnetosheath and magnetotail data are routinely interpreted as evidence of developed turbulence. But if ponderomotive effects suppress the inertial range, the observed spectra may reflect the dissipation structure rather than the cascade dynamics. The measurement sees the endpoint, not the process.