Three-dimensional numerical models are established to investigate the effects of capsule sag and shift on its thermal environment in cryogenic target with micro filling tubes. The simulation bases on Boussinesq hypothesis and a discrete ordinates radiation model. Variations of the target temperature and velocity distributions are studied when the capsule and its gas filling tube are offset in the vertical and horizontal directions and effects of gas filling tube
shimming heating and thermal radiation on the shift-and-sag sensitivity are analyzed. The results show that the gas filling tube has a significant effect on the surface temperature uniformity of the capsule
and the maximum temperature differences on the outer surface of the capsule with single filling tube and two opposite filling tubes increase by 78.9% and 76.7% respectively
compared with no filling tube configurations. For the case of the single filling tube
the capsule temperature uniformity can be improved when the target is offset vertically within a certain distance. Under given conditions
the optimal offset distance for maximum uniformity improvement is 5 μm
while the horizontal offset of 112 μm is allowed for the single gas filling tube configuration. With an increase in shimming heating power
the optimal offset distance in the vertical direction is almost unchanged
but the tolerance of the horizontal shift of the target increases. As to the thermal radiation
the larger the transmittance of sealing films is
the more sensitive the capsule temperature to the target offset is
along with the larger temperature difference.
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references
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