Scientific rationale and main objectives of the task. The objectives of the Task Agreement are reported in the following. WP09-MHD-01-01 (WP III-1-a): Improve confidence in predictions of fast particle stability boundaries in ITER and model confined/escaping fast ions seen in present experiments. Fast particles interact with MHD waves for on one hand they may drive or stabilize MHD instabilities (destabilization of Toroidal Alfvén Eigenmodes or Energetic Particles Modes and stabilization of sawtooth are just two examples), and on the other hand MHD instabilities affect confinement of fast particles. In ITER, for instance, the alpha-particle partial pressure may be significant enough to induce collective instabilities leading to energy confinement degradation and first wall damage due high alpha particle fluxes. Therefore, understanding the physics of these fast particles (in particular in presence of a significant population of them) and in general of fast ions is one of the key issues for controlling burning plasmas. On present-day machines there is an urgent need to understand the mechanisms of fast ion transport (this has clear consequences for example on NBI heating and current drive efficiency) and the nonlinear behaviour of multiple Alfvén modes since they may be also destabilised in ITER.
Scientific rationale and main objectives of the task. The objectives of the Task Agreement are reported in the following. Unmitigated disruptions represent an intolerable risk for ITER and should be avoided by a reliable control of the plasma discharge. However the understanding of how to predict and avoid such events is at a rudimentary level since extensive development of avoidance and control techniques has not been envisaged on existing devices. In addition, an extrapolation of the effects of a disruption from existing devices to ITER is affected by uncertainties which must be reduced to guarantee the integrity of the machine. The joint exercise carried out by JET and AUG for developing a technique capable of predicting each other disruptions was encouraging but not accurate enough to be promising for ITER despite the fact that their present disruption recognition system, based on a locked mode detector which does not need any training, is rather reliable. WP09-MHD-02-01 (WP III-2-a): Prediction of disruptions based on a physical model and development of diagnostics for disruption studies Develop a disruption prediction model based on simple and robust real-time measurements of physical quantities and on recognition algorithms related to physics laws and to well- established empirical behaviour. Compare the effectiveness of the model with the neutral network approach. WP09-MHD-02-02 (WP III-2-a) Phase I: Fast measurements of impurity radiation during disruptions - Includes a Call for Interest. Develop diagnostics techniques aiming at quantifying the influx of impurities from the plasma facing components during the disruption and understand the penetration of injected impurities in mitigated events. WP09-MHD-02-03 (WP III-2-a-2): Simulation of VDEs using XXXX to validate the halo current models. Validate the halo current models using simulations of VDEs with the XXXX code. Benchmark the XXXX code using data from an ITER relevant device. Validate or refute the assumptions presently made when XXXX is applied to ITER by means of the widest possible use of XXXX on existing devices, where experimental measurements are available.
Scientific rationale and main objectives of the task. The objectives of the Task Agreement are reported in the following. WP09-MHD-03-01 (WP III-2-b):
Scientific rationale and main objectives of the task. The objectives of the Task Agreement are reported in the following. WP09-MHD-04-01 (WP III-3-a-1, a-5, a-4, a-3): ELMs: Physics Understanding, Non_linear MHD and Pellet induced ELMs, Resonant magnetic field perturbation (RMP) stabilisation of ELMs. The onset of large ELMs is broadly accepted to be usually associated with the triggering of peeling-ballooning modes, and codes can predict the threshold and the structure of these instabilities, including many of the key parameter dependencies, with considerable precision. However, there are important physics aspects that need further investigation, including the effect of toroidal rotation and details physics of ELMs in the different regimes. Crucial questions surrounding ELM mitigation using the pellet technique is the ability to achieve the ELM frequency increase required on ITER: of the order of 10 times when compared to unmitigated ELM frequencies Remaining key questions to be addressed include the understanding of the action of edge resonant magnetic field perturbation on ELMs, as a function of general parameter variations such as plasma shape and density. These studies could require some further code developments, and improved measurements such as edge currents and plasma rotation. This task would benefit from co-ordination of joint projects to make the comparisons between model and experiments.
Scientific rationale and main objectives of the task. The objectives of the Task Agreement are reported in the following.
