Ohshima S, Suzuki T, Matoike R, Motojima G, Kado S, Mori A, Miyashita A, Kobayashi S, Minami T, Iwata A, Qiu D, Wang C, Luo M, Zhang P, Kondo Y, Nishino N, Mizuuchi T, Okada H, Konoshima S, Inagaki S, Nagasaki K
Institute of Advanced Energy, Kyoto University, Kyoto, 611-0011, Japan.
Graduate School of Energy Science, Kyoto University, Kyoto, 611-0011, Japan.
Sci Rep. 2022 Aug 20;12(1):14204. doi: 10.1038/s41598-022-18239-z.
Understanding pellet ablation physics is crucial to realizing efficient fueling into a high temperature plasma for the steady state operation of ITER and future fusion reactors. Here we report the first observation of the formation of fluctuation structures in the pellet plasmoid during the pellet ablation process by a fast camera in a medium-sized fusion device, Heliotron J. The fluctuation has a normalized fluctuation level of ~ 15% and propagates around the moving pellet across the magnetic field. By comparing the fluctuation structures with the shape of magnetic field lines calculated with the field line tracing code, we successfully reconstruct the spatio-temporal structure of the fluctuations during the pellet ablation process. The fluctuations are located at the locations displaced toroidally from the pellet and propagate in the cross-field direction around the pellet axis along the field line, indicating a three-dimensional behavior and structure of fluctuations. The fluctuation would be driven by a strong inhomogeneity formed around the pellet and invoke the relaxation of the gradient through a cross-field transport induced by the fluctuations, which could affect the pellet ablation and pellet fueling processes. Such fluctuations can be ubiquitously present at the inhomogeneity formed around a pellet in the pellet ablation process in fusion devices.
理解弹丸消融物理对于实现向高温等离子体高效注入燃料以维持国际热核聚变实验堆（ITER）及未来聚变反应堆的稳态运行至关重要。在此，我们报告了在中型聚变装置Heliotron J中，通过高速摄像机首次观测到弹丸消融过程中弹丸等离子体团内波动结构的形成。该波动的归一化波动水平约为15%，并在移动弹丸周围沿磁场方向传播。通过将波动结构与用场线追踪代码计算出的磁力线形状进行比较，我们成功重建了弹丸消融过程中波动的时空结构。这些波动位于相对于弹丸在环向有位移的位置，并沿着磁力线围绕弹丸轴在横向场方向传播，表明波动具有三维行为和结构。这种波动可能由弹丸周围形成的强不均匀性驱动，并通过波动引起的横向场输运促使梯度弛豫，这可能会影响弹丸消融和弹丸燃料注入过程。在聚变装置的弹丸消融过程中，这种波动可能普遍存在于弹丸周围形成的不均匀性处。
