Abstract
The parallel expansion of a dense, pellet-produced plasmoid is modelled with parameters relevant to pellet fuelling experiments in the Wendelstein7-X stellarator. Good agreement is found between the analytical theory and more detailed modelling. In particular, much of the energy deposited in the pellet by the ambient plasma is transferred to the pellet ions by the ambipolar electric field during the expansion. The validity of the hydrodynamic treatment of the plasmoid and the ambient plasma is discussed.
Highlights
IntroductionPellet injection into fusion devices is useful for particle supply (fuelling) and discharge termination
Pellet injection into fusion devices is useful for particle supply and discharge termination
In this work we focus on the long-term evolution of the plasmoid, so that the long mean free path of the ambient plasma particles in a heated plasmoid prevents us from treating the ambient plasma hydrodynamically
Summary
Pellet injection into fusion devices is useful for particle supply (fuelling) and discharge termination. We use a hybrid (two-component) approach to study the expansion of the pellet-produced plasmoid: we simulate the cold plasmoid with a Lagrangian fluid code and describe the rarefied hot plasma kinetically. This approach was proposed by Rozhansky & Veselova (1994) and adopted by Parks, Sessions & Baylor (2000). The hot plasma acts as a collisional volumetric source of energy for the plasmoid This model extends the work of Aleynikov et al (2019) by including ion heating into the picture. We demonstrate a good agreement between the analytical and the numerical models within the appropriate applicability range
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