A New Approach to SOL Broadening by Turbulence Spreading.

The need to escape from the pessimistic scalings of the HD SOL width model has

boosted interest in turbulent pedestal states which drive SOL broadening by turbulence

spreading. Here we discuss a spectral intensity theory of SOL broadening by turbulence spreading.

The theory links the SOL scale to dynamics of the pedestal — in particular, to the

turbulence energy influx across the separatrix. The broadening of the layer-specifically the layer

width as a function of turbulence intensity- is calculated,

and the result is non-trivial, with a cross-over between two asymptototic trends. The HD result is recovered

for weak turbulence levels.We show

that modest levels of drift wave turbulence (i.e. Grassy ELMs) can adequately broaden the

SOL. We also present a novel approach to SOL turbulence spreading, based upon

dissipative, stochastic turbulence pulses. In contrast to familiar avalanche models ,a

key feature here is the absence of a conserved parameter, due to finite SOL dwell time.

The theory links SOL broadening to the intensity gradient at the separatrix. Results for the

statistical distribution of pulse penetration depths will be discussed.We derive a criterion for

the formation of SOL structure in turbulence . Implications for experiments will be discussed.