Abstract
In order to investigate the ablation of a solid hydrogen pellet, which is injected into a high-temperature plasma with high speed (∼1km∕s) for the plasma refueling, a three-dimensional observation system using a fast camera has been developed. A stereo method has been employed to obtain the three-dimensional information of the pellet ablation. A pair of the stereo images, which have been taken from different locations, has been focused onto a single fast camera by using a bifurcated fiber scope to ensure the simultaneity of both images. The projection matrix, which is used for stereo reconstruction, is calibrated by taking images of a model plane of known coordinates from the actual camera positions. The measuring error of the stereo observation is within 2% in the depth direction.
Highlights
Pellet injection has a potential for high-efficiency fueling in a magnetically confined high-temperature plasma since it can supply the hydrogen directly to the core plasma
Pellet injection has extended the operational regime to higher densities while maintaining favorable confinement properties
In order to optimize the pellet fueling based on an understanding of the mechanism, it is important to investigate the pellet ablation and subsequent drift of the ablatant
Summary
Pellet injection has a potential for high-efficiency fueling in a magnetically confined high-temperature plasma since it can supply the hydrogen directly to the core plasma. The fact that the pellet massdeposition profile is skewed toward the edge when compared to the measured pellet penetration depth and the pellet ablatant promptly drifts towards the low-magnetic-field direction, have been confirmed in several experiments These phenomena suggest that the behavior of the pellet ablatant can be a critical issue in considering the fueling efficiency. In order to optimize the pellet fueling based on an understanding of the mechanism, it is important to investigate the pellet ablation and subsequent drift of the ablatant For this purpose, three-dimensional observation with a high sampling rate is needed since the pellet ablation related phenomena are relatively short 共typically less than 10−3 s兲 and the spatial structure of the pellet ablatant changes continuously while moving, which is caused by interaction with the plasma and the confining magnetic field in addition to the initial injection inertia. The camera calibration has been carried out to minimize the error due to lens distortion, image digitalization, etc
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