The heating of tungsten monoblocks at the ITER divertor vertical targets is calculated using the heat flux predicted by three-dimensional ion orbit modelling. The monoblocks are beveled to a depth of 0.5 mm in the toroidal direction to provide magnetic shadowing of the poloidal leading edges within the range of specified assembly tolerances, but this increases the magnetic field incidence angle resulting in a reduction of toroidal wetted fraction and concentration of the local heat flux to the unshadowed surfaces. This shaping solution successfully protects the leading edges from inter-ELM heat loads, but at the expense of (1) temperatures on the main loaded surface that could exceed the tungsten recrystallization temperature in the nominal partially detached regime, and (2) melting and loss of margin against critical heat flux during transient loss of detachment control. During ELMs, the risk of monoblock edge melting is found to be greater than the risk of full surface melting on the plasma-wetted zone. Full surface and edge melting will be triggered by uncontrolled ELMs in the burning plasma phase of ITER operation if current models of the likely ELM ion impact energies at the divertor targets are correct. During uncontrolled ELMs in pre-nuclear deuterium or helium plasmas at half the nominal plasma current and magnetic field, full surface melting should be avoided, but edge melting is predicted.

No abstract

Measurements of ion energies in the boundary of tokamak plasmas in L-mode discharges and during ELMs are reviewed. A profile of the ion-to-electron temperature ratio e i T / T from the edge of the confined plasma into the scrape-off layer (SOL) is produced by compiling the available i T measurements. The picture that emerges is that in the SOL, as well as in the edge, i T is systematically higher than e T (ratios up to 10 just outside the last closed flux surface) for most plasma parameter regimes. Far SOL ELM ion energies measured in JET, and more recently in MAST and AUG, agree with the models of the ELM transients, providing strong evidence that ELM ions can reach the first wall with significant fraction of the pedestal energies.3

No abstract

No abstract

No abstract

No abstract

Abstract. Using the Retarding Field Analyser (RFA) technique, ion energies carried by ELM filaments have been measured for the first time in the far scrape-off layer (SOL) of the ASDEX Upgrade tokamak. Energies, ELM i E, exceeding 160 eV have been found, 5 -6 cm outside the separatrix, with a decay length of about 2 cm. The measured ELM particle ion temperature in the far SOL is in the range 80 50 − ≈ IntroductionThermal heat loads to the first wall during edge localized modes (ELMs) have been identified as one of the important issues for ITER burning plasma operation and determine the design of the ITER blanket module shaping and power handling capacity [1]. These heat loads scale with the energies carried by ELM ions to the first wall, which, in turn, depend on dissipation by parallel losses of the ELM energy to the divertor targets as the ELM particles travel across the SOL. Direct measurements of the ELM ion energies in the far SOL are, therefore, important in order to constrain the models of the ELM parallel transport in the SOL [2,3], which, in turn, increases the confidence in the model predictions towards ITER.Earlier measurements of the heat loads to the first wall in ASDEX Upgrade (AUG) revealed that up to~25% of the energy lost per ELM can be deposited on non-divertor components, indicating that ELM ions can carry relatively large fractions of the energy with which they are released into the SOL to the first wall [4,5,6]. These observations (also seen later on JET [7,8]), were consistent with increase by an order of magnitude of the tungsten influx from the outboard limiters in AUG during ELMs compared to inter-ELM periods [9]. Energetic ELM ions (impact energies exceeding 400 eV) in the far SOL (typically 2-3 characteristic SOL power widths outside the separatrix) were measured directly for the first time in JET [10] (and more recently in MAST [11]) using a Retarding Field