Speaker
Description
Robust operation of the ITER Electron Cyclotron (EC) system, including avoidance of damage to launcher and in-vessel components, is essential to achieve ITER’s mission goals. The main purpose of the system is to provide EC heating (ECH) and current drive (ECCD) to heat and control the plasma in order to enhance its performance and ensure its stability. ECH/ECCD is essential during ITER pre-fusion power operation phases to provide power for H-mode access, central heating to prevent W accumulation, for the stabilisation of Neoclassical Tearing Modes (NTMs) and, during DT operation, to achieve a high fusion gain and to shape the current profile for hybrid and steady-state scenarios. In all operation phases of the ITER Research Plan (IRP), it is essential to minimise the heat loads on in-vessel components due to EC power losses, to maximise plasma performance and to prevent damage to the machine. For this purpose, a consolidated strategy is being established [1]. EC stray losses impact the launchers themselves, motivating dedicated studies for the optimisation of their optical design [2], but they also impact plasma performance. In the plasma, EC stray radiation is due to reduced optical thickness – e.g. when EC is applied during the current ramp-up phase – and to cross-polarization, leading to incomplete single pass absorption, or to reflections at the density cut-off layer.
The IRP is currently being revised as part of a re-baselining proposal [3] which consists of beginning operation with an Augmented First Plasma (AFP) phase, during which the blanket first wall will be inertially cooled only, the beryllium first wall material will be replaced by tungsten (W) and the available EC power to the plasma will be doubled to 40 MW, injected through a single Equatorial Launcher (EL) and three Upper Launchers (UL). For the Fusion Power Operation (FPO) phases (also called DT phases), for which the four ULs will be available, a further increase of the available EC power to 67 MW is proposed as risk mitigation to counter potential issues arising from enhanced core tungsten W impurity concentrations. To accommodate this power increase, a second EL is also planned. In FPO the wall will be actively cooled. Excessive EC power losses would be problematic in both AFP and FPO phases, since an inertially cooled wall can sustain only comparatively low heat loads for any reasonable duration and a water-cooled wall is prone to water leaks. For this reason EC heat loads are one of the design drivers for the temporary panels, and it is thus essential to quantify them. This is performed here using the TORBEAM beam-tracing code [5] within the ITER Integrated Modelling and Analysis Suite IMAS [6], to simulate ECH, ECCD and stray losses, for various IRP scenarios. An earlier, similar study was performed based on the existing ITER baseline [7]. The present analysis includes additional parametric scans to quantify the ECH/ECCD efficiency for various BT/Ip operational points, and various poloidal and toroidal launch angles in view of optimising the design for the second EL in FPO phases. This new study is also key to the optimisation of the path towards nominal Ip and BT operation in the revised IRP.
