Experimental investigation of the dynamics of a vibrating grid in superfluid 4He over a range of temperatures and pressures.
Experimental investigation of the dynamics of a vibrating grid in superfluid 4He over a range of temperatures and pressures.
复制标题
在一定温度和压力范围内超流体 4He 中振动网格动力学的实验研究。
DOI：
10.1103/physreve.74.036307
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
W. Vinen
中科院分区：
文献类型：
--
作者：
D. Charalambous;L. Skrbek;P. C. Hendry;P. McClintock;W. Vinen
在较早的论文[Nichol，Phys. Rev. E，70，056307（2004）]中，一些作者提出了在同位素纯超流体4 He中，在压力范围内，在非常低的温度下，在正常流体的密度可以忽略不计的情况下，在其共振频率或接近其共振频率处驱动振动的拉伸网格的动力学的实验研究结果。在本文中，我们提出了一个类似的研究结果，基于不同的网格，但现在包括正常的流体密度不再是微不足道的温度范围。新网格与旧网格非常相似，除了其表面粗糙度的特征有很小的差异。在许多方面，低温下的结果与旧网格的结果相似。在低振幅下，结果在某种程度上取决于历史，但本质上没有比真空中更大的阻尼。在对应于约50 <$（-1）速度的临界振幅处，阻尼突然大幅度增加，这可归因于新涡线的产生。用旧网格观察到的中间振幅处的共振频率的奇怪变化不再被看到，但是它们因此必须与不同的表面粗糙度相关联，或者可能仅仅是由于旧网格的一些伪影，其细节我们目前无法确定。与新的网格，我们已经研究了阻尼在低振幅由于正常流体的激励，和超临界阻尼对温度的依赖性。我们提出的证据表明，在低振幅的氦气中，除了与氦气的势流相关的有效质量之外，网格的有效质量可能会有一些增强。在某些情况下，小卫星谐振附近的主要基本网格谐振，这是由于耦合到一些其他的振荡系统的实验细胞。
In an earlier paper [Nichol, Phys. Rev. E, 70, 056307 (2004)] some of the present authors presented the results of an experimental study of the dynamics of a stretched grid driven into vibration at or near its resonant frequency in isotopically pure superfluid 4He over a range of pressures at a very low temperature, where the density of normal fluid is negligible. In this paper we present the results of a similar study, based on a different grid, but now including the temperature range where the normal fluid density is no longer insignificant. The new grid is very similar to the old one except for a small difference in the character of its surface roughness. In many respects the results at low temperature are similar to those for the old grid. At low amplitudes the results are somewhat history dependent, but in essence there is no damping greater than that in vacuo. At a critical amplitude corresponding to a velocity of about 50 mms(-1) there is a sudden and large increase in damping, which can be attributed to the generation of new vortex lines. Strange shifts in the resonant frequency at intermediate amplitudes observed with the old grid are no longer seen, however they must therefore have been associated with the different surface roughness, or perhaps were due simply to some artifact of the old grid, the details of which we are currently unable to determine. With the new grid we have studied both the damping at low amplitudes due to excitations of the normal fluid, and the dependence of the supercritical damping on temperature. We present evidence that in helium at low amplitudes there may be some enhancement in the effective mass of the grid in addition to that associated with potential flow of the helium. In some circumstances small satellite resonances are seen near the main fundamental grid resonance, which are attributed to coupling to some other oscillatory system within the experimental cell.