Thermally-driven scintillator flow in the SNO+ neutrino detector
Thermally-driven scintillator flow in the SNO+ neutrino detector
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DOI：
10.1016/j.nima.2023.168430
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发表时间：
2022-12
期刊：
影响因子：
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通讯作者：
J. Wilson
中科院分区：
文献类型：
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作者：
J. Wilson
SNO+中微子探测器是一个丙烯酸球体（半径6米），有一个细长的垂直颈，包含近800吨的液体闪烁体。该装置浸泡在一个充满水的地下洞穴中，颈部向上伸出到水面以上的歧管中，闪烁体填充球体，并上升约6米，与净化的氮气接触面相连。对瞬态氡（222 Rn）污染层的观测激发了对闪烁体流体的对流运动进行了随时间的流动模拟，该污染层在两周内从颈部底部附近下沉到探测器的赤道。根据模拟，这种运动可能是由通过探测器壁的热传递引起的，这导致了薄壁边界层内的浮力上升流和其他地方的补偿汇。这种机制可以导致在几个小时的时间尺度上从颈部向下传输到球体。如果闪烁体恰好是热分层的，那么微弱的壁面热流所施加的同样的力会在球形流域中产生内部重力波，频率为Brunt-Väisälä。然而，由于振荡运动本质上是非扩散的，模拟证实，在颈部深度施加强烈的热分层可以减轻由于瞬态热通量引起的混合。
The SNO+ neutrino detector is an acrylic sphere (radius 6 m) with a thin vertical neck containing almost 800 tonnes of liquid scintillator. The apparatus is immersed in a water-filled underground cavern, the neck protruding upward into a manifold above water level, with scintillator filling the sphere and rising up the neck some 6 m to an interface with purified nitrogen gas. Time-dependent flow simulations have been performed to investigate convective motion of the scintillator fluid, motivated by observations of a transient radon (222 Rn) contamination layer which, over a period of two weeks, sank from near the base of the neck to the detector’s equator. According to simulations, this motion may have been induced by heat transfer through the detector wall, that resulted in buoyant ascending flow within a thin wall boundary layer and compensating sink elsewhere. This mechanism can result in transport down the neck to the sphere on a time scale of several hours. If the scintillator happens to be thermally stratified, the same forcing by a weak wall heat flux produces internal gravity waves in the spherical flow domain, at the Brunt–Väisälä frequency. Nevertheless as oscillatory motion is by its nature non-diffusive, simulations confirm that imposing strong thermal stratification over the depth of the neck can mitigate mixing due to transient heat fluxes.