Speaker
Description
Detached plasmas are essential for controlling heat and particle fluxes to the plasma-facing components of magnetic fusion devices. We have studied the fundamental processes during detached plasma operations in the divertor simulation experimental module (D-module), using a variable-angle V-shaped target plate at the end-loss region of the tandem mirror plasma device GAMMA 10/PDX [1,2]. Recently, different configurations of diverter shapes have been examined, including compact diverter structures to maintain core plasma volume [3] and methods to spread heat loads using a long-leg diverter [4]. In both cases, the ratio of the target plate area in contact with the plasma and/or the surrounding wall area to the plasma volume is high. Molecular Dynamics simulations have indicated that hydrogen atoms and molecules produced from the diverter plate are excited [5], and, because they are highly reactive, their atomic and molecular reactions near the surface increasingly influence the formation of detached plasma.
So far, we have observed that increasing H₂ pressure expands the hydrogen molecular activated recombination (MAR) area near the target plate. Recently, further increases in gas pressure have led to strong emissions from highly excited states [2]. These findings emphasize the importance of surface reactions, including the mutual neutralization of H₂+ and H, and the formation of vibrationally excited H₂. Therefore, atomic and molecular processes are considered to involve reactions on the target and wall surfaces that generate excited molecules. Plasma-gas-surface interactions are also crucial to the formation of detached plasma. To accurately understand the reaction process, further issues include the need for detailed measurements of the energy states of hydrogen atoms and molecules, especially near the target plate.
In this study, we adjusted the small angle (~15 deg) of the V-shaped target plate to enhance the influence of the surface. We investigated spectroscopic measurements near the V-shaped target, with particular focus on hydrogen molecular emission. The dependence on the distance from the target plate was also examined. These experiments involved heating the V-shaped target plate from room temperature up to 573 K to observe changes in the surface reaction. In this presentation, we will discuss these results and show the impact of different strike point positions.
This work was partly supported by JSPS KAKENHI Grant Numbers 22H01198 and 23K22469 and the NIFS Collaboration Research program (NIFS23KUGM174, NIFS23KUGM186, NIFS25KFFT001).