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The possibility of driving a large fraction of the plasma current in a tokamak reactor employing electron cyclotron waves is investigated for scenarios as envisaged in the European DEMO through beam tracing calculations performed with the TORBEAM code, which assumes a linear regime for power absorption and employs an adjoint method for the determination of the driven current. Comparatively high ECCD efficiency in the inner half of the plasma column can be achieved by injecting the wave from an elevated position. On the other hand, the efficiency deteriorates in the colder, outer part of the plasma, so that a prohibitive amount of power would be needed to sustain the plasma current non-inductively by ECCD only in the considered scenarios. As an alternative scheme, the injection of slow extraordinary wave below the fundamental resonance is considered. The basic physics features of this scenario are discussed.

The flight simulator predicts the dynamic behavior of a full plasma discharge (described in terms of one-dimensional profiles) by employing multiple control loops based on synthetic diagnostics, which could also emulate realistic sensor and actuator models. It serves as a valuable tool for designing and optimizing plasma scenarios, as well as for assessing the feasibility of controlling discharges. The Fenix flight simulator, originally developed for the ASDEX Upgrade, has been ported to EU-DEMO and is capable of modeling any tokamak. One of the essential elements in a flight simulator is the link between the co-simulated plasma physics and the control loops. This element is tightly coupled to the specifications of both the plasma model and the control algorithms to be implemented; but on the other hand, to ensure the portability and applicability of the flight simulator to different scenarios or devices, the coupling between plasma and control algorithms should be neutral to any concrete device and configuration. In addition, as a serial component of the control loop, data exchange takes place at every single step of the control simulation, therefore an efficient implementation is critical for the overall simulation performance. This paper summarizes the universal approach recently implemented in Fenix, which satisfies all the above requirements while remaining lightweight. [ABSTRACT FROM AUTHOR]

Internal kink (IK) instability is investigated for European demonstration fusion reactor (EU DEMO) plasmas in both negative triangularity (NT) and positive triangularity (PT) configurations. For NT plasmas, the IK becomes more unstable as an ideal conformal wall moves away from the plasma boundary, with the mode growth rate saturating at the wall radial location of about , where a is the plasma minor radius and b the wall radial location. The plasma resistivity destabilizes the IK mode. The effect of sub-sonic toroidal plasma flow is sufficiently weak and can thus be ignored for these EU DEMO equilibria. These results are consistent with those for PT plasmas, albeit with larger mode growth rate in the NT configuration. Both perturbative and self-consistent magneto-hydrodynamic (MHD)-kinetic hybrid calculations predict (partial) stabilization of the IK modes in both NT and PT configurations, with inclusion of various kinetic contributions. Precessional drift motion of trapped fusion-born alphas in EU DEMO produces weak stabilization to the IK mode. Stronger stabilization occurs with the toroidal precession of trapped thermal particles (ions and electrons) and the bounce-transit motion of thermal ions. The stabilization is similar between the NT and PT configurations, due to the similarity of the mode eigenfunction (occupying a nearly circular region in the plasma core) despite the sign difference in the triangularity. The non-perturbative MHD-kinetic hybrid model predicts much less stabilization of the mode than the perturbative model, primarily due to the self-consistent determination of the mode eigenvalue in the former. Generally, no significant difference in the IK mode stability is found between the NT and PT plasmas in EU DEMO. [ABSTRACT FROM AUTHOR]

The sawtooth activity is investigated for an EU DEMO reference plasma, including kinetic effects from both thermal particles and fusion-born alphas. Kinetic effects are studied in conjunction with modification of the magnetic shear near the q= 1 surface (q is the safety factor) due to local current drive. Kinetic stabilization on the internal kink mode is found by both the non-perturbative MHD-kinetic hybrid code MARS-K (Liu et al 2008 Phys. Plasmas 15 112503) and the perturbative semi-analytic Porcelli model. The latter predicts full stabilization of the mode, when the local magnetic shear s1 at the q= 1 surface is less than 1 (e.g. s1 ∼ 0.6 as is the case for the target EU DEMO plasma without local current drive). By increasing the local magnetic shear with local current drive up to s1 ∼ 2.8, one of the Porcelli sawtooth crash criteria can be satisfied, by accessing the ion-kinetic regime. Direct MARS-K non-perturbative eigenvalue computations, on the other hand, predict less kinetic stabilization of the internal kink and more robust triggering of the sawtooth crash in EU DEMO. The general trend of the predicted results remains similar though, between the MARS-K model and the Porcelli model. [ABSTRACT FROM AUTHOR]