Spatiotemporal analysis of detached plasma response to electron beam injection using laser Thomson scattering

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Abstract
Transient heat loads like Edge Localized Modes (ELMs) can degrade detached plasmas that are essential for reducing divertor heat fluxes in future fusion reactors. To investigate the response of detached plasmas to transient electron energy deposition, a pulsed electron beam was injected into a detached helium plasma in the linear plasma device NAGDIS-II. Spatiotemporal evolutions of electron temperature and density were measured using laser Thomson scattering synchronized with the beam injection with high-temporal resolution. Despite the small beam source diameter (2 mm), significant changes in plasma parameters extended over a wide radial range (> 15 mm). The electron beam rapidly increased the electron temperature near the plasma center, resulting in a local transition from a recombining plasma to an ionizing plasma. In contrast, the electron density exhibited a slower temporal evolution, suggesting different underlying mechanisms governing temperature and density responses. The measured spatiotemporal plasma parameters were further analyzed using a collisional-radiative model and reproduced previously observed line-integrated emission dynamics. These results demonstrate that localized electron energy deposition can induce a global response in detached plasmas and provide new insight into the stability and dynamic behavior of detached plasmas subjected to transient energy loads.
Funding Information
  • Japan Society for the Promotion of Science (21KK0048)
  • Japan Society for the Promotion of Science (22K18701)
  • Japan Society for the Promotion of Science (23K22474)
  • Japan Society for the Promotion of Science (24H00201)
  • National Institute for Fusion Science (NIFS25KIPI010)
  • National Institute for Fusion Science (NIFS25KRCT002)
  • The Public Foundation of Chubu Science and Technology Center