2025 – Exploration of EDA H-mode Operational Space Towards ITER Relevant Conditions

Exploration of EDA H-mode Operational Space Towards ITER Relevant Conditions

2025 Research Campaign, Transient Control

Purpose of Experiment

In this experiment a H-mode scenario free of Edge-Localized Modes (ELMs), the so-called Enhanced-D-alpha (EDA) regime will be explored. The main limitation of the EDA H-mode is it’s narrow power window, which can be widened by strong shaping. At higher separatrix collisionality and shaping close to a double null plasma, the EDA H-mode is thought to transition into the Quasi-Continuous Exhaust (QCE) regime. A scenario with small high frequent pedestal relaxation events. The goal of this experiment is to investigate the effect of shaping on the EDA H-mode power window in order to enable low collisionality operation. Furthermore, the transition and access to QCE H-mode will be studied.

Experimental Approach

Starting from a target discharge that achieved a stationary EDA H-mode, every single discharge will have power steps between 1-6MW. First, we investigate to effect of different heating systems: on-axis Electron Cyclotron Heating (ECH), off-axis ECH, co-Ip Neutral Beam Injection (NBI) and balanced NBI. Then the flattop density will be increased to find access to the QCE regime at the high power steps. Then a wide scan of plasma shaping parameters will be covered. That includes changing the bias from lower single null closer to double null, varying the elongation and also scanning the upper and lower triangularity. With this approach not only the effect on the power window of the EDA H-mode can be studied, but simultaneously data on the transition to QCE H-mode as well as the effect of shaping on the access to QCE H-mode can be investigated.

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