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The successful operation of ITER advanced scenarios is likely to be a major step forward in the development of controlled fusion as a power production source. ITER advanced scenarios raise specific challenges that are not encountered in presently-operated tokamaks. In this thesis, it is argued that ITER advanced operation may benefit from optimal control techniques. Optimal control ensures high performance operation while guaranteeing tokamak integrity. The application of optimal control techniques for ITER operation is assessed and it is concluded that robust optimisation is appropriate for ITER operation of advanced sce- narios. Real-time optimisation schemes are discussed and it is concluded that the necessary conditions of optimality tracking approach may potentially be appropriate for ITER operation, thus offering a viable closed-loop optimal control approach. Simulations of ITER advanced operation are necessary in order to assess the present ITER design and uncover the main difficulties that may be encountered during advanced operation. The DINA-CH&CRONOS full tokamak simulator is used to simulate the operation of the ITER hybrid and steady-state scenarios. It is concluded that the present ITER design is appropriate for performing a hybrid scenario pulse lasting more than 1000s, with a flat-top plasma current of 12MA, and a fusion gain of Q ∼= 8. Similarly, a steady-state scenario without internal transport barrier, with a flat-top plasma current of 10MA, and with a fusion gain of Q ∼= 5 can be realised using the present ITER design. The sensitivity of the advanced scenarios with respect to transport models and physical assumption is assessed using CRONOS. It is concluded that the hybrid scenario and the steady- state scenario are highly sensitive to the L-H transition timing, to the value of the confinement enhancement factor, to the heating and current drive scenario during ramp-up, and, to a lesser extent, to the density peaking and pedestal pressure.
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limited'' configuration, where the main plasma touches the reactor wall, and the contact point defines the Last Closed Flux Surface (LCFS). In this thesis, we advance the understanding of SOL physics in limited plasmas, combining experiments and numerical simulations. In particular, two topics are addressed. First, the separation between the near'' and ``far'' SOL is investigated. The near SOL extends typically a few mm from the LCFS, features steep radial profiles of parallel heat flux and is responsible for the peak of heat deposition on the tokamak first wall. The far SOL, typically a few cm wide, features flatter heat flux profiles, and accounts for the majority of the heat deposited on the first wall. Secondly, blob dynamics is investigated. Blobs are high density plasma filaments generated by turbulence, and are an ubiquitous feature of plasmas in open magnetic field lines. The blobs travel outwards to the reactor walls, increasing the cross field transport. Dedicated experiments have been performed on the TCV tokamak. Inboard-limited Deuterium (D) and Helium (He) plasma discharges are performed, varying the main plasma parameters (current, density and shaping). The parallel heat flux radial profiles are determined with infrared thermography. For the first time, the presence of a near SOL in TCV limited plasmas is reported, both for D and He discharges. The near SOL is found to disappear for high plasma resistivity. Non-ambipolar currents are measured to flow to the wall in the near SOL using Langmuir probes, and their presence is found to correlate with the strength of the near SOL heat fluxes. A simple interpretation is given. The heat fluxes and electric potentials are also measured on the low field side using a reciprocating Langmuir probe, and compared with the ones measured on the tokamak wall. A method for the mitigation and suppression of the near SOL heat fluxes through impurity seeding is proposed, and first experimental evidences are presented. The experiments are compared with numerical simulations of the TCV SOL, performed with the GBS code. The simulated parallel heat flux profiles qualitatively agree with the experimental ones, showing the presence of a near and far SOL. Also, non-ambipolar currents are observed to flow to the wall. The effect of resistivity is investigated through a second simulation with a 40 times higher resistivity. The blob dynamics in TCV is investigated using a conditional average sampling technique on the reciprocating Langmuir probe data. The results for two discharges, for low and high resistivity respectively, are discussed. A blob detection and tracking algorithm is applied to the numerical simulation outputs, and the results are discussed.