content_image/342756.jpg content_image/342757.jpg content_image/342758.jpg
A schematic sketch of the equilibrium pedestal profiles, representing an idealised ASDEX Upgrade H-mode scenario [42], is shown in Fig. 2 together with the final relaxed state after the ELM blowout phase (which is discussed in the next section). 

## VI. COMPUTATION OF THE ELM BLOWOUT 

When this initialised pedestal pressure profile is ideal ballooning unstable, the IBM in- stability in GEMR simulations is observed to be linearly growing in the pedestal region and at the onset of nonlinearity further overshoots and saturates, representing the beginning of the turbulent blowout phase during which a substantial fraction of the pedestal energy is thrown onto the SOL. Subsequent evolution involves turbulence in both the pedestal and SOL regions as the original pedestal energy is dissipated. 

Previous nonlinear approaches on ELM ideal ballooning mode burst computations have treated only the initial growth and nonlinear phases, focused on low-wavelength modes and resolved only the MHD-relevant scales, excluding treatment or discussion of the ion gyro- radius scales. This however precludes the development of fully developed microturbulence which is caused by the onset of nonlinearity (robust transfer of free energy to smaller scales). Ultimately, this microturbulence decides both the transition to nonlinearity and the eventual saturation; that is, most of the post-peak transport curve. This affects the MHD scenario of nonlinear explosive growth which most previous work advances. However, we find that the exclusion of the ion gyroradius scales produces an under-resolved situation. 

We measure the quantitative character of the growth in both linear and nonlinear phases with a growth curve 

<img src='content_image/342756.jpg'>

defined in terms of the heat flux Q$_{i}$ instead of the fluctuation free energy as explained above. The heat flux is computed as a zonal (flux surface) average, 

<img src='content_image/342757.jpg'>

<img src='content_image/342758.jpg'>

and then the time trace Q$_{i}$ ( t ), normalised in terms of p$_{e}$c$_{s}$ at nominal parameters, is com- puted as a volume average over the central half of the radial domain. 

