ITER breakdown and plasma initiation revisited

作者：P.C. de Vries, Y. Gribov · 发表于：Nuclear Fusion · 年份：2019 · DOI：10.1088/1741-4326/ab2ef4 · 被引用次数：71 · 研究领域：Magnetic confinement fusion research、Particle accelerators and beam dynamics、Plasma Diagnostics and Applications

This paper revisits a number of key aspects of plasma initiation, aiming to clarify concepts, provide definitions and improve understanding, in view of ITER First Plasma operation. It shows that size matters and that breakdown and plasma initiation differ in larger devices. The large thick and conductive ITER vessel slows down the prefill process, the development of the toroidal electric field and affects the dynamics of the poloidal magnetic field at breakdown. The large vacuum vessel requires more than 1 s for the prefill gas to spread over the vessel. It slows down the development of the toroidal electric field, applied to ionize the prefill gas, by about 1 s and complicates the control of the magnetic configuration required for plasma initiation. It is shown that the avalanche process that provides the initial ionization slows down towards the end, if the cross-section of the toroidal discharge is larger. On the other hand, a larger plasma volume is beneficial for the subsequent burn-through of main-species ionization and impurity line-radiation. ITER First Plasma operation aims to reach a minimum plasma current of 100 kA, which will require a full avalanche and a partial burn-through to reach electron temperatures of at least 10–20 eV. The burn-through limits the ITER prefill pressure upper range of about 1 mPa. These predictions are based on 0D models of plasma initiation that furthermore assume the plasma volume remains constant. As burn-through is a critical process, ...