Integrated Scenario with Type-III ELMy H-mode Edge: Extrapolation to ITER

One of the most severe problems for fusion reactors is the power load on the plasma facing components. The challenge is to develop operation scenarios, which combine sufficient energy confinement with benign heat loads to the plasma facing components. The radiative type-III ELMy H-mode seems a possible solution for such an integrated ITER scenario. Most notably the transient heat loads due to type-III ELMs are acceptable with even the most stringent boundary conditions. For instance, on JET the transient heat loads due to type-III ELMs onto the outer divertor target were reduced to 2kJ per square meter. Scaled to ITER, type-III ELMy H-modes are expected to have a power load of approximately 0.3MJ per square meter transiently. This was achieved in experiments carried out with nitrogen seeding to mitigate the transient and steady state heat flux to the divertor. Typically the confinement is reduced by ~ 8-20% compared to the type-I ELMy H-mode base scenario. However, increasing the plasma current to 17MA on ITER and hence reducing the edge safety factor to 2.6, would allow Q = 10 operation at a reduced confinement enhancement factor. This operation scenario was demonstrated at JET up to plasma currents of 3.25MA. At the highest plasma current the effective charge Zeff can be as low as 1.4, mainly due to the increased absolute density and reduced carbon erosion. A large database of highly radiative type-III ELMy H-modes on JET is used for extrapolations to ITER. The data set shows no apparent dependence of the confinement enhancement factor on collisionality. The scaling of the confinement time with respect to the ion gyro radius is close to gyro-Bohm scaling. The 'hybrid' regime, designed for high beta stationary scenarios, has been extended recently at JET to the type III-ELMy H-mode operation by nitrogen seeding (at a plasma current of 1.7MA) up to a normalized pressure (beta) of 2.6. Similar to the standard ELMy H-mode the confinement enhancement factor is reduced by about 20%. The''hybrid' type III-ELMy H-mode scenario shows improved edge plasma condition without significant modification of the q-profile (stabilized near unity in the plasma core in order to reduce the sawteeth activity), indicating it is compatible with high beta operation (optimized for current drive sources). Extrapolations to ITER are done with an integrated core/edge model.
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