Development of a Plasma Scenario for the EU-DEMO: Current Activities and Perspectives

In order for the first fusion reactor DEMO to accomplish its mission [1], it is necessary to identify plasma scenarios which both perform in terms of fusion power generation and are sufficiently stable to ensure the integrity and availability of the machine components for a long time.The activities undertaken for this purpose by EUROfusion Power Plant Physics & Technology (PPP&T) are summarized in this paper.Throughout the course of the current pre-conceptual design analysis phase for the European DEMO, it is necessary to define scenarios by considering from the early phases their compatibility with the available diagnostics, of the actuators for plasma control and with the response of the heating and current drive systems.A coupling between the 1D transport code ASTRA [2,3,4] and the control software Simulink has been performed, providing a tool able of simulating plasma behaviour while accounting for the constraints linked to the detectability of the signals and the delay and power limitations of the actuators responses [5].In parallel, the numerous ongoing activities concerning the open issues which require addressing are reviewed.The reference scenario which is considered for the EU-DEMO is the so called "DEMO 1" [6], i.e. a pulsed configuration based on conservative physics assumptions and analogous, at least from a macroscopic level, to the ITER 15 MA ELMy-H mode.The main alternative concept developed is the so called Flexi-DEMO [7], which relies on a more advanced scenario compared to DEMO 1, with a large fraction of auxiliary current drive and a tailoring of the safety factor profile, in order to maximize the bootstrap current fraction and thus to achieve a long, or even steady-state discharge.However, the significant difficulties linked to an active ELM control suggest that other, more speculative ELM-free scenarios [8,9,10,11] might be more suitable for a reactor operationin spite of their reduced fusion performance.1.