old, still allowing the ITG instability because the adiabatic response does not involve the ions. The ITG instability exists at all α$_{M}$ values, and furthermore for the edge situation the ITG instability and mode structure transitions smoothly to a drift wave one in a nonlinear setting for η$_{i}$ ∼ 1. Hence there is actually no finite threshold in values of η$_{i}$ or α$_{M}$ for the nonlinear edge situation. Therefore, the existence of a threshold in the experiment is the same as the mechanism which maintains the H-mode, which is not yet well understood. It follows that a gyrofluid model computation of an ELM scenario with enough resolution to allow for ion-gyroradius based dynamics has to face the lack of a simple linear threshold in the parameter space. 

The transition from initial (micro-)instabilities to generic edge turbulence was studied in detail in Ref. [41]. As the most unstable linear modes crystallise out of an initial random bath of small-amplitude perturbations, the linear growth rate rises and becomes steady. The maximum value of the instantaneous growth rate of total fluctuation free energy E given by Γ( t ) = (1 / 2 E )( ∂E/∂t ) may be taken as the maximal linear growth rate. The curve of Γ( t ) then falls very sharply to zero (over about 10 L$_{⊥}$/c$_{s}$ ) as saturation occurs. There is some structural adjustment over the next few 100 L$_{⊥}$/c$_{s}$ as the spectrum fills out, and then the turbulence is fully developed. But over the adjustment phase the value of Γ is well below its previous maximum. We will use the same diagnostic herein, except that the total ion ExB heat flux Q$_{i}$ averaged over the computational domain is used instead of E because most of E is represented by the self consistent profiles while Q$_{i}$ is entirely due to fluctuations. 

The IBM ELM blowout scenario is similar to this, initially, except that the instability is not a microinstability. Nevertheless, the scale differs by less than an order of magnitude: the toroidal mode numbers for linear ITG instabilities are in the range of n = 30 − 100 while the main ideal ballooning mode is near mode number n = 10, on the entire flux surface, for these typical ρ$_{s}$/L$_{⊥}$ values (recall ρ$_{s}$ = ρ$_{i}$ for T$_{e}$ = T$_{i}$ , and the ratio T$_{i}$/T$_{e}$ is not far from unity in experimental cases). The ITG mode numbers are determined by the ion gyroradius and the dimensionless scale ratio L$_{T}$ /qR , while the MHD values are determined by the width of the pedestal. Since L$_{T}$ is not larger than about 30 ρ$_{i}$ in an H-mode pedestal, these scales are not disparate. 

Due to the closeness of the native scales, the IBM instability very quickly transfers energy to the ion gyroradius scale, which is only about two or three steps away in a turbulence cas- cade which acts at a factor of two at each step. This brings the ITG and drift Alfv´ en physics 

