Characteristics of type I ELM energy and particle losses in existing devices and their extrapolation to ITER

Abstract

Analysis of Type I ELMs from ongoing experiments shows that ELM energy losses are correlated with the density and temperature of the pedestal plasma before the ELM crash. The Type I ELM plasma energy loss normalized to the pedestal energy is found to correlate across experiments with the collisionality of the pedestal plasma (ν * ped ), decreasing with increasing ν * ped . Other parameters affect the ELM size, such as the edge magnetic shear, etc, which influence the plasma volume affected by the ELMs. ELM particle losses are influenced by this ELM affected volume and are weakly dependent on other pedestal plasma parameters. In JET and DIII-D, under some conditions, ELMs can be observed ('minimum' Type I ELMs with energy losses acceptable for ITER), that do not affect the plasma temperature. The duration of the divertor ELM power pulse is correlated with the typical ion transport time from the pedestal to the divertor target (τ Front || = 2πRq 95 /c s,ped ) and not with the duration of the ELMassociated MHD activity. Similarly, the timescale of ELM particle fluxes is also determined by τ Front ||. The extrapolation of the present experimental results to ITER is summarized.

In-vessel saddle coils for MHD control in ASDEX Upgrade

“…The energy loss associated with Edge Localised Modes (ELMs) in ITER might exceed the tolerable limit of ∆W ELM ≈ 10 MJ to avoid evaporation of C or W wall [1]. The scaling of ELM loss energy is not known, but present data suggests an unfavourable dependence on pedestal collisionality ν * [2]. Techniques to avoid large ELMs are therefore being investigated, for example ELM loss reduction by injection of cryogenic pellets [3], small ELM regimes [4][5][6] and stationary ELM-free regimes [7,8].…”

Dynamics of erosion and deposition in tokamaks

“…High quality H-modes are usually associated with type I ELMs, which can release a substantial fraction ΔW ELM of stored energy to the wall (ΔW ELM /W of up to ~10%). Such repetitive events will likely cause unacceptable high erosion of the plasma-facing components (PFCs) [7,8], thus negatively affecting the availability of ITER. Investigations of specific carbon and tungsten materials proposed for ITER PFCs have resulted in ELM loads being further restricted to 0.5 MJ/m 2 [9], corresponding to ΔW ELM ~ 1 MJ in ITER.…”

Particle, heat, and sheath power transmission factor profiles during ELM suppression experiments on DIII-D

“…Edge localized modes (ELMs) are predicted to be a problem for ITER due to resulting high levels of impulse heating and erosion of the target plates [1,2]. Using a resonant magnetic perturbation (RMP), ELMs have been suppressed in DIII-D [3].…”