Effect of neutral and ion temperatures in the 2D fluid model for the RF heated ion source SPIDER

This paper presents the basic physical and numerical principles of a fluid model implemented into numerical code FSFS2D (Fluid solver for source for the production of ions of deuterium extracted from rf plasma (SPIDER) in 2D) used for simulating the SPIDER negative ion source. It gives self-consistent 2D description of the source, including the neutral gas flow, plasma chemistry, radio-frequency (RF) coupling in the source driver and plasma transport through the magnetic filter. This paper focuses on the recent developments of the plasma model and the first simulations showing the role of the neutrals and ions temperature equations on the source performance are presented. The upgraded model is validated against SPIDER Langmuir-probe measurements and shows reasonable agreement for the axial plasma profiles. The new heavy-species temperature equations reveal strong differences between atoms, molecules, and ions, with D (Formula presented) (Formula presented) temperatures increasing in low-density regions near the plasma grid. The simulations provide insight into the energy exchange mechanisms between plasma species and show that only about one third of the RF power transferred to electrons is consumed by plasma-chemical reactions. Atomic deuterium and positive ions are heated mainly through chemical processes, whereas molecules and negative ions are heated predominantly by elastic collisions. Parametric studies demonstrate the sensitivity of heavy-species temperatures to RF power, gas pressure, and magnetic-filter strength.