这项工作得到了美国能源部SLAC合同号的支持。DE-AC02-76SF00515 以及美国能源部科学办公室，聚变能源科学根据 FWP 100182。这项工作还得到了美国国家科学基金会第1632708号拨款和EC H2020 LASERLAB-EUROPE / LEPP（合同号654148）的部分支持。CBC感谢加拿大自然科学和工程研究理事会（NSERC）的支持。F.T.感谢国家核安全局（NNSA）的支持。

以下协议详细介绍了在 17 K、60 psig 下操作的 5 μm 直径圆柱形低温氢气射流的组装和操作作为示例案例。将该平台扩展到其他孔径类型和气体需要在不同的压力和温度下运行。作为参考，表1中列出了其他射流的工作参数。第 1-3 节和第 7 节在环境温度和压力下进行，而第 4-6 节在高真空下进行。
1. 在真空室中安装低温恒温器
注意：真空容器可能会对人员和设备造成危险，因为倒塌、回填加压导致破裂或真空窗口故障导致内爆。泄压阀和爆破盘必须安装在低温系统内的真空容器上，以防止过压。
<ol><li>小心地将低温恒温器插入真空室。使用稳定平台将低温恒温器与真空室振动隔离。</li>
	<li>进行真空测试以确定基线真空压力，我们发现该压力必须优于~5 x 10-5 mBar。残余气体分析仪（RGA）通常有助于识别系统中存在的水分和污染气体。</li>
	<li>将温度控制器和加热器连接到低温恒温器，并确认在环境温度下读数准确。<ol><li>如果测量到意外值，请验证从温度传感器到温度控制器上正确端子的连续性。否则，请更换温度传感器。</li>
	</ol></li>
	<li>将氦气回流管连接到可调节流量计面板。</li>
	<li>使用由干涡旋泵支持的涡轮分子泵将传输线上的绝缘真空罩排空至优于 1 x 10-2 mBar。</li>
	<li>在低温恒温器头部内的 O 形圈上涂上一层薄薄的低温真空润滑脂。</li>
	<li>慢慢将传输线冰箱卡口插入低温恒温器，直到调节螺钉接触低温恒温器头。阻力应该最小。拧紧调节螺钉，将冰箱卡口上的针阀设置到所需位置。</li>
	<li>进行低温恒温器性能测试，通过冷却到可达到的最低温度来验证温度传感器的可靠性。如果在冷却期间测量到意外温度，请目视检查温度传感器是否与低温恒温器接触良好。如有必要，重新定位并涂抹低温真空润滑脂以改善接触。</li>
	<li>根据图1中的P&ID 图组装样品气体管路。使用高灵敏度检漏仪识别任何泄漏。 注意：氢气、氘和甲烷是极易燃气体。使用设计用于承受压力和物理危害的管道和设备。需要局部排气或通风以保持浓度低于爆炸极限。在对任何其他气体应用此过程之前，请查阅相关的安全数据表 （SDS）。</li>
	<li>根据连续流吹扫技术吹扫气体管线，将污染气体和水蒸气稀释至样品气体的纯度。总时间取决于给定背压下的气体管路体积和气体流量。 注意：吹扫管路时，请确保真空室充分通风或在真空下保持，以防止易燃气体积聚。</li>
	<li>初始吹扫完成后，在管路上保持恒定的正压（例如，在 50 psig 时为 30 sccm），以降低真空室处于环境压力时污染物气体进入管路的风险。</li>
</ol>2. 安装低温源部件
注意：低温源组件的所有准备和组装都应在干净的环境中使用适当的洁净室服装（即手套、发网、实验室外套等）进行。
<ol><li>使用间接超声波清洗去除低温源组件中的污染物（例如残留的铟）。<ol><li>用蒸馏水填充超声仪并添加表面活性剂以降低水的表面张力。</li>
		<li>将低温源部件放入单个玻璃烧杯中，将其完全浸没在电子级异丙醇中，并用铝箔松散地覆盖烧杯，以减少蒸发并防止颗粒污染。</li>
		<li>将烧杯放入清洁篮或超声仪中的烧杯支架中，以最大限度地提高气蚀。烧杯不应接触超声仪的底部。</li>
		<li>激活超声仪60分钟。</li>
		<li>使用明亮的白光检查异丙醇是否有悬浮颗粒或残留物。</li>
		<li>如果可见颗粒，请用干净的异丙醇冲洗部件，并更换异丙醇浴。以60分钟的周期进行超声处理，直到没有可见的颗粒或残留物。</li>
		<li>将零件放在有盖的清洁表面上，在组装前干燥至少 30 分钟。</li>
	</ol></li>
	<li>对不锈钢过滤器、源盖、套圈和装配螺钉重复第 2.1 节。</li>
	<li>切一块铟，最大限度地覆盖低温源体和低温恒温器冷手指之间的连接处。</li>
	<li>将铟放在低温源上，并用低温恒温器的冷手指将其保持齐平。拧紧固定螺钉，确保铟保持平坦，以在组件之间建立热密封。不要拧得过紧，因为铜线很容易损坏。</li>
	<li>将螺纹不锈钢过滤器拧到低温源法兰上。</li>
	<li>将铟垫圈放在源法兰上。使用法兰螺钉将源法兰连接到低温源体。对角拧紧螺钉，而不是围绕圆周依次拧紧螺钉。</li>
	<li>将低温恒温器上的样品气体管线连接到低温源。使用高灵敏度检漏仪检查泄漏。</li>
</ol>3. 孔径的安装
<ol><li>根据实验需要选择光圈。<ol><li>使用明场和暗场显微镜技术检查孔径，以识别孔径中的缺陷、物理障碍物或残留的光刻胶。</li>
		<li>用异丙醇冲洗时，可以轻松清除一些物理障碍物。否则，请丢弃光圈。</li>
		<li>如果孔径的纳米制造中有残留的光刻胶，请使用丙酮浴或食人鱼溶液将其去除。 注意：食人鱼溶液由3：1硫酸（H 2 SO4）和过氧化氢（H2O2）组成，对有机物质（包括皮肤和呼吸道）具有极强的腐蚀性。食人鱼与有机物质的反应释放出气体，可能会爆炸。切勿密封装有食人鱼的容器。需要全面罩、耐化学腐蚀围裙、实验室外套和氯丁橡胶手套。</li>
	</ol></li>
	<li>用电子级异丙醇冲洗孔径，以去除任何碎屑或表面污染。安装前，让孔在干净和覆盖的表面上干燥 10 分钟。</li>
	<li>将套圈放在盖子内。</li>
	<li>使用干净的软镊子将孔圈放置在套圈内。轻拍盖子，使孔圈在套圈中居中。</li>
	<li>将铟环放在光圈顶部。再次点击盖子的边缘，将铟环置于光圈的中心。</li>
	<li>用手将盖子拧紧到源法兰上，直到检测到最小的阻力。</li>
	<li>通过将设定值增加到 500 sccm 来取消质量流量控制器上的流量限制，并在压力调节器上将气体压力设置为 ~50 psig。</li>
	<li>使用扳手一次将孔径精细地拧紧几度，直到流速开始降低。</li>
	<li>通过使用高灵敏度检漏仪而不是质量流量控制器检查盖子顶部的泄漏率来完成盖子的拧紧。拧紧不再降低测得的泄漏率时停止。</li>
	<li>如果流速未低于大约 50 sccm，请继续执行以下步骤。<ol><li>使用检漏仪检查源法兰和盖子周围的泄漏。重新拧紧源法兰上的螺钉并重新测量泄漏率。</li>
		<li>取下盖子并检查源法兰的孔径和尖端。</li>
		<li>如果光圈损坏，请按照步骤2.2清洁盖子并重复第3节。</li>
		<li>如果铟环固定在孔径上，则丢弃孔径并重复第 3 部分。</li>
		<li>如果完整的铟环固定在法兰上，请使用干净的塑料剃须刀片刮掉残留的铟，然后重复步骤3.2-3.10。</li>
		<li>随着时间的推移，铟可能会积聚在源法兰的尖端，从而阻止后续孔密封。在这种情况下，拆下源法兰并重复第 2.1-2.2 节，然后执行步骤 2.5-2.7。</li>
	</ol></li>
	<li>作为安全预防措施，将质量流量控制器上的设定值更改为比由孔径尺寸确定的最终流量高 10 sccm。</li>
</ol>4. 冷却程序
<ol><li>验证真空室压力是否已达到给定样品气体流量的预期基线。为了确保没有污染气体，这些气体会在冷却过程中沉积在低温源上，通常在达到基线压力后将真空室泵送至少 1 小时。该持续时间随当地湿度水平和真空系统而变化。</li>
	<li>打开低温恒温器排气加热器，以防止低温恒温器头因氦气回流而结霜。</li>
	<li>通过将设定值增加到 500 sccm 来取消质量流量控制器上的气体流量限制。</li>
	<li>用液氮填充开式循环冷阱。确保液氮液位始终高于在线过滤器。在冷却和喷射操作期间根据需要进行监控和加注。 注意：接触低温液体，如液氮或液氦，会灼伤皮肤、面部和眼睛。处理大量低温液体（多升）时，请佩戴面罩、安全眼镜、隔热低温手套、低温围裙、无袖口长裤和露趾鞋。这种液体可能会置换氧气并导致快速窒息。</li>
	<li>将氦气回流管路上的可调流量计设置为完全打开。</li>
	<li>使用排气阀对液氦杜瓦瓶进行减压。</li>
	<li>关闭液氦杜瓦瓶上的低压泄压阀的球阀。冷却期间推荐的杜瓦瓶压力为 10 psig。杜瓦瓶适配器上的角阀允许操作员在样品液化后有多余的冷却功率时降低杜瓦瓶压力。</li>
	<li>以一个平稳的动作将供应杜瓦卡口插入液氦杜瓦瓶中。当卡口接触液体时，杜瓦瓶应加压至 10 psig。 注意：始终保持所有暴露的皮肤远离杜瓦瓶的颈部。</li>
	<li>使用检漏仪拧紧连接后，检查杜瓦瓶和杜瓦瓶适配器之间的氦气泄漏。</li>
	<li>激活温度控制器上的加热器并将温度设定值设置为 295 K。</li>
	<li>一旦传输管线充满并冷却，低温恒温器温度将从环境温度降至 295 K，此时加热器将激活以防止温度进一步下降。请注意，初始温度下降所需的时间取决于杜瓦瓶压力、总传输管线和低温恒温器长度。</li>
	<li>将温度控制器上的斜坡速率设置为 0.1 K/s，将设定值设置为 200 K.调节氦气流量以跟随斜坡，使加热器不打开。在 200 K 下保持短暂停留段（例如 5 分钟），以使低温恒温器热化。重复两个额外的斜坡停留段，达到 120 K，然后达到 40 K。采用保守的冷却程序来避免沿系统出现强烈的温度梯度，并允许密切监控系统参数。停留温度选择在远离污染气体的升华温度的地方。<ol><li>如果气流意外增加，则源法兰或孔径上的铟密封可能已失效。通过继续执行步骤 6.4 中止冷却过程。真空室排气后，检查密封件并参考第 3.10 节重新拧紧并检查是否有泄漏。</li>
	</ol></li>
	<li>在40 K时，按照齐格勒-尼科尔斯方法22 手动调整温度控制器P-I-D参数，直到温度稳定性优于±0.02 K。</li>
</ol>5. 液化和喷射操作
<ol><li>确认液氮液位高于在线过滤器。</li>
	<li>禁用温度斜坡并将设定点温度更改为远低于理论气液相变温度（例如，氢气为 20 K）。</li>
	<li>在液化开始时，气流将增加到最大，气体和液体的混合物将从孔径中喷出。增加氦气流量以提供额外的冷却功率，以快速通过相变。</li>
	<li>使用具有脉冲亚纳秒照明的高倍率阴影成像来可视化射流稳定性和层流度23.</li>
	<li>可选：如果应用或实验具有样品的预定位置（例如，检测器与空间中的相同位置对齐），请使用低温恒温器法兰上的多轴机械手或真空室中的电动推针执行器来平移低温源。</li>
	<li>平移捕手以最大化捕手前线的压力。</li>
	<li>优化P-I-D参数和氦气流量，将温度稳定性提高到优于±0.02 K.请注意，射流的整体稳定性在很大程度上取决于真空室压力，气体背衬压力和温度。例如，小至 1 x 10-5 mBar 的变化可能需要重新优化。</li>
	<li>扫描温度和压力以优化射流稳定性和层压度。样品射流参数列于表1中。<ol><li>如果射流分解成喷雾，相空间中的压力和温度可能太接近汽化曲线。</li>
		<li>大振幅温度或氦气流振荡将导致周期性的空间扰动，这（在极端情况下）会导致射流的驱动破碎。减少氦气流量并重新优化P-I-D参数以抑制振荡。</li>
		<li>如果射流表现出横向（即第一风状态）或纵波（即高原-瑞利不稳定），则降低温度以增加粘度，从而减少雷诺数。</li>
		<li>如果无法实现层流，并且射流特性与温度和压力的变化无关，则孔径中可能存在物理障碍（例如物理碎片或冰）。在中止测试之前，请按照步骤6.1-6.5并密切监测真空压力和低温恒温器温度。如果污染物气体或水在孔径上升华导致部分或全部堵塞，则可以通过蒸发温度来识别。重复步骤 4.11-4.12 和 5.1-5.6 以确定射流稳定性是否提高。</li>
	</ol></li>
</ol>6. 预热程序
注意： 如果在操作过程中孔径损坏，请立即将样品气体流量限制在 10 sccm，并将样品气体压力降低到 30 psig。然后，直接进入步骤 6.5。
<ol><li>将设定值更改为 20 K，并将气体压力从工作压力降低到大约 30 psig。</li>
	<li>以 1 K 的步长增加温度设定值，同时监测气体调节器上的压力。当低温源中的液体汽化时，气体管路中的压力将迅速增加，通过质量流量控制器的流量将读取0 sccm。 注意： 不要让气体压力超过样气管路上组件的最大工作压力。如果发生这种情况，请等到管路通过孔径或泄压阀减压到安全值，然后再进一步增加设定值。</li>
	<li>重复步骤6.2，直到将温度设定值提高1 K不会导致气体管路压力增加。</li>
	<li>启用温度斜坡，将温度设定值更改为 300 K，并根据需要调节氦气流量以保持 0.1 K/s 的温度升高。</li>
	<li>一旦源温度高于 100 K，关闭氦气回流管路上的可调流量计。给杜瓦瓶减压，将球阀打开到最低泄压阀。</li>
	<li>等到低温恒温器在 300 K 下热化后再向真空室通风。这将防止水蒸气凝结在低温恒温器和低温源组件上。</li>
	<li>给杜瓦瓶减压，然后拆下供应杜瓦卡口。</li>
	<li>拆下液氮冷阱。</li>
	<li>将质量流量控制器上的气体流量限制为 30 sccm。</li>
	<li>关闭废气加热器。</li>
	<li>停用温度控制器上的加热器。</li>
	<li>如果光圈损坏或因流量变化而怀疑阻塞，请继续执行第 7 部分。否则，不需要更换光圈。</li>
</ol>7. 更换光圈
<ol><li>取下盖子并检查源法兰的孔径和尖端。</li>
	<li>如果铟环粘在法兰上，请使用干净的塑料剃须刀片使用中等压力将其刮掉。</li>
	<li>如果取下盖子时孔径仍然密封在源法兰上，请将气体流量限制在 10 sccm，并确认气体背衬压力已降至 30 psig。用塑料剃须刀片小心地取下光圈。如果过早移除，管路中的过压可能会损坏或弹出孔径。</li>
	<li>重复第 3 节以安装新光圈。</li>
</ol>

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作者没有什么可透露的。

低温液体射流的成功运行需要一丝不苟的清洁度和对温度稳定性的仔细监测。最常见和可避免的故障之一是微米级孔径的部分或全部堵塞。来自源或空气中颗粒的铜、不锈钢或铟可以在源组件的任何步骤中引入。所有组件必须经过使用间接超声处理的稳健清洁过程。在 10,000 级或更好的洁净室中进行组装和存储可提高成功率。
该程序的另一个关键步骤是稳定低温源温度。用户必须确保离开源的液体温度的测量独立于储层中连续液化释放的可变热量。这是通过将温度传感器放置在孔径附近（例如，在源法兰上）或远离热源来实现的。此外，必须使用齐格勒-尼科尔斯方法针对每种温度和背衬压力组合手动优化 P-I-D 参数。如果温度波动变得太大，可以在射流上观察到周期性振荡，有时会导致周期性分解。应该注意的是，内置的自动整定功能或低通滤波器在喷射操作期间未能成功稳定温度。
低温液体喷射系统虽然适应性强，但在具有既定真空协议的大型设施中实施具有挑战性。例如，当上游设备对残余气体敏感时，需要差动泵级（例如，DESY的闪光自由电子激光器或SLAC的MeV-UED仪器）。此外，大直径真空室，例如用于多PW激光器的真空室，可能需要真空中柔性低温恒温器。与传统的固定长度低温恒温器相比，它们可以很容易地与腔室振动分离，并且具有更短的杠杆臂。在亥姆霍兹-德累斯顿-罗森多夫中心（HZDR）已经使用Draco Petawatt激光器实施了灵活的真空低温恒温器。另一个观察结果是，当射流被离光源太近的超高强度激光照射时，孔径可能会损坏。最近，已经实施了一种机械斩波刀片（工作频率为150 Hz并与激光脉冲同步），以保护孔径免受激光-等离子体相互作用的影响。
该系统可产生微米级、高度可调、无湍流、层流圆柱形和平面低温液体射流。低温液体射流系统的持续开发侧重于先进的孔径材料和设计、真空系统和捕集器的改进以及先进的氢同位素混合。该系统将能够过渡到高重复率高能量密度科学，并为下一代粒子加速器的发展铺平道路。

该方法的目标是产生由纯元素或化合物组成的高速低温液体流动。由于低温液体在环境温度和压力下蒸发，因此以高重复率（例如，1 kHz）操作的残留样品可以从真空室中完全排出1。基于格里森蒂等人的初步工作。2、该系统最早是利用低温氢进行高强度激光驱动质子加速开发的3.它随后被扩展到其他气体并用于许多实验，包括：离子加速4,5，回答等离子体物理学中的问题，例如等离子体不稳定性6、氢7 和氘中的快速结晶和相变，以及 meV 非弹性 X 射线散射8 以解析直线加速器相干光源 （LCLS） 的极端条件下物质 （MEC） 仪器中的氩气声波 9。
到目前为止，已经开发了其他替代方法来生成高重复率的固体低温氢和氘样品。Garcia等人开发了一种方法，其中氢气在储层中液化和固化，并通过孔径10挤出。由于挤出所需的高压，（迄今为止）展示的最小样品厚度为62μm11。该系统还表现出较大的空间抖动12。最近，Polz等人使用435 psig（磅/平方英寸，仪表）的样品气体背衬压力，通过玻璃毛细管喷嘴产生低温氢气射流。由此产生的10μm圆柱形射流是连续的，但看起来波纹很大13。
这里介绍的是一种生产具有各种纵横比（1-7 μm x 10-40 μm）的圆柱形（直径 = 5-10 μm）和平面射流的方法。指向抖动随与光圈5 的距离呈线性增加。流体性质和状态方程决定了可以在该系统中操作的元素和化合物。例如，由于瑞利破裂，甲烷不能形成连续射流，但它可以用作液滴14。此外，最佳压力和温度条件因孔径尺寸而异。以下段落提供了生产层流、无湍流低温氢射流所需的理论。这可以扩展到其他气体。
低温射流系统由三个主要子系统组成：（1）样品气体输送，（2）真空，以及（3）低温恒温器和低温源。 图1 所示的系统设计为高度适应安装在不同的真空室中。
气体输送系统由超高纯压缩气瓶、气体调节器和质量流量控制器组成。样气的背衬压力由气体调节器设定，而质量流量控制器用于测量和限制输送到系统的气体流量。首先在液氮冷阱中过滤样品气体，以冷冻出污染气体和水蒸气。第二个在线微粒过滤器可防止碎屑进入气体管线的最后一段。
涡轮分子泵背靠高抽速涡旋泵，可在样品室中保持高真空条件。腔室和前部真空压力分别使用真空计 V1 和 V2 进行监测。应该注意的是，当液体蒸发时，操作低温射流会向真空系统引入大量的气体负荷（与总样品流量成比例）。
减少气体负荷的一种行之有效的方法是在发生大量汽化之前捕获残留液体。射流捕集器系统由一条独立的真空管线组成，该真空管线端接由距离低温源盖最远 20 mm 的 ø800 μm 差分泵送孔径终止。管路使用在 1 x 10-2 mBar 范围内表现出最佳效率的泵（即罗茨鼓风机真空泵或混合涡轮分子泵）抽真空，并由真空计 V3 监控。最近，捕手允许高达 7 μm x 13 μm 的低温氢气射流运行，真空室压力提高了两个数量级。
固定长度、连续流动的液氦低温恒温器用于将源冷却到低温。液氦是使用传输线从供应杜瓦瓶中抽取的。回流连接到可调节的流量计面板以调节冷却功率。冷手指和低温源的温度由四个引线硅二极管温度传感器测量。比例积分微分 （P-I-D） 温度控制器向安装在冷手指附近的加热器提供可变电压，以调节和稳定温度。样气通过低温恒温器法兰上的定制馈通件进入真空室。在腔室内，气体管线缠绕在低温恒温器周围以预冷气体，然后连接到低温源组件上的固定气体管线。不锈钢螺钉和 51 μm 厚的铟层将低温源热密封到冷手指上。
低温源（图2）由六个主要部件组成：（1）样气管路，（2）源体，（3）带在线微粒过滤器的源法兰，（4）孔径，（5）套圈和（6）盖。源体包含一个空隙，用作样品储液器。带螺纹的世伟洛克烧结 0.5 μm 不锈钢过滤器可防止任何碎屑或固化污染物进入液体通道并阻塞孔径。在孔径和液体通道之间放置一个较厚的76μm厚的铟环，以增加变形长度并可靠地密封孔径。当盖子拧到源法兰上时，铟被压缩以形成液体和热密封。套圈和源盖在安装过程中使孔径居中。
在连续层流状态下运行的低温液体射流系统的初始设计中，有许多总体考虑因素。用户必须估计低温恒温器的总冷却功率、低温源设计的热特性、真空系统性能以及液体温度和压力。下面提供的是所需的理论框架。
冷却功率注意事项
1）液化氢15：将氢气从300K液化到一定温度 <img alt="Equation 2" src="/files/ftp_upload/61130/61130eq2v2.jpg" style="font-size: 14px;">所需的最小冷却功率可以使用以下公式粗略估计： <img alt="Equation 1" src="/files/ftp_upload/61130/61130eq1v3.jpg">
其中：<img alt="Equation 3" src="/files/ftp_upload/61130/61130eq3v2.jpg">是恒压<img alt="Equation 4" src="/files/ftp_upload/61130/61130eq4v2.jpg">下的比热，和H2在压力依赖性液化温度<img alt="Equation 6" src="/files/ftp_upload/61130/61130eq6v2.jpg">下的汽化潜热。<img alt="Equation 5" src="/files/ftp_upload/61130/61130eq5v2.jpg">例如，在 60 psig 气体压力下运行并冷却至 17 K 的低温氢气射流至少需要 4013 kJ/kg。氢气流量为 150 sccm（标准立方厘米每秒），这相当于 0.9 W 的<img alt="Equation 7" src="/files/ftp_upload/61130/61130eq7v2.jpg">热量。
应该注意的是，液化过程仅占所需总冷却功率的十分之一。为了减少低温恒温器上的热负荷，气体可以在进入源体之前预冷到中间温度。
2）辐射热：为了将低温源保持在一定温度 <img alt="Equation 2" src="/files/ftp_upload/61130/61130eq2v2.jpg">，低温恒温器需要补偿辐射加热。这可以通过使用以下公式平衡发射和吸收的黑体辐射的差异来估计： <img alt="Equation 8" src="/files/ftp_upload/61130/61130eq8v2.jpg">
其中：A是源体的面积，是斯特凡-玻尔兹曼常数， <img alt="Equation 9" src="/files/ftp_upload/61130/61130eq9v2.jpg"> <img alt="Equation 10" src="/files/ftp_upload/61130/61130eq10v2.jpg">是真空室的温度。例如，A = 50 cm 2 冷却至 17 K 的典型射流源需要2.3 W 的最小冷却功率。 <img alt="Equation 10" src="/files/ftp_upload/61130/61130eq10v2.jpg">可以通过添加覆盖大部分低温源的主动冷却辐射屏蔽来局部减少。
3）残余气体传导：尽管热辐射在超高真空条件下占主导地位，但在射流操作期间，残余气体传导的贡献变得不可忽视。液体射流在腔室中引入大量气体负荷，导致真空压力增加。气体在压力 p 下热传导的净热损失使用以下公式计算： <img alt="Equation 11" src="/files/ftp_upload/61130/61130eq11v2.jpg">
其中：<img alt="Equation 12" src="/files/ftp_upload/61130/61130eq12v2.jpg">是取决于气体种类的系数（H2 为 ~3.85 x 10-2 W/cm2/K/mBar），<img alt="Equation 13" src="/files/ftp_upload/61130/61130eq13v2.jpg">并且是取决于气体种类、源的几何形状以及源和气体的温度的调节系数16,17。当在 17 K 下操作低温氢气射流时，假设源的圆柱形几何形状并且氢气是真空室中存在的主要气体，气体传导会产生热量，可以使用以下公式估算： <img alt="Equation 14" src="/files/ftp_upload/61130/61130eq14v2.jpg">
例如，在 4.2 x 10-3 mBar 的真空压力下，气体传导产生的热量与热辐射一样多。因此，在喷射操作期间，真空压力通常保持在 1 x 10-3 mBar 以下，为系统增加 ~0.55 W 的热负荷 （A = 50 cm2）。
运行期间引入腔室的气体负荷是通过低温射流获得的。然后，产生的真空压力由真空系统的有效抽速和真空室的体积确定。
为了操作低温射流，低温恒温器必须产生足够的冷却功率来补偿上述不同的热源（例如，3.75 W），不包括低温恒温器系统本身的热损失。请注意，低温恒温器效率也在很大程度上取决于所需的冷手指温度。
估算射流参数
要建立连续的层流，必须满足几个条件。为简洁起见，此处显示了圆柱形液体流动的情况。平面射流的形成涉及额外的力，导致更复杂的推导，超出了本文的范围18。
1）压力-速度关系：对于不可压缩的液体流动，能量守恒产生伯努利方程，如下所示： <img alt="Equation 15" src="/files/ftp_upload/61130/61130eq15v2.jpg">
其中：<img alt="Equation 16" src="/files/ftp_upload/61130/61130eq16v2.jpg">是流体原子密度，是流体速度，是重力势能， <img alt="Equation 18" src="/files/ftp_upload/61130/61130eq18v2.jpg"> <img alt="Equation 17" src="/files/ftp_upload/61130/61130eq17v2.jpg"> p是压力。在整个孔径上应用伯努利方程，可以使用以下公式估计射流速度和样品背衬压力之间的函数关系： <img alt="Equation 19" src="/files/ftp_upload/61130/61130eq19v2.jpg">
2）射流操作制度：圆柱形液体射流的制度可以用雷诺数和欧内佐格数推断出来。雷诺数定义为流体内惯性和粘性力之间的比值，使用以下公式计算： <img alt="Equation 20" src="/files/ftp_upload/61130/61130eq20v2.jpg">
其中： <img alt="Equation 16" src="/files/ftp_upload/61130/61130eq16v2.jpg">、、、 <img alt="Equation 17" src="/files/ftp_upload/61130/61130eq17v2.jpg">和 分别是流体的密度、速度、 <img alt="Equation 21" src="/files/ftp_upload/61130/61130eq21v2.jpg">直径和 <img alt="Equation 22" src="/files/ftp_upload/61130/61130eq22v2.jpg">动态粘度。当雷诺数小于~2,000时发生层流。同样，韦伯数将惯性的相对大小与表面张力进行比较，并使用以下公式计算： <img alt="Equation 23" src="/files/ftp_upload/61130/61130eq23v2.jpg">
其中：σ是液体的表面张力。然后按如下方式计算欧内佐格数： <img alt="Equation 24" src="/files/ftp_upload/61130/61130eq24v2.jpg">
该与速度无关的量与雷诺数结合使用，以识别四种液体射流状态：（1）瑞利，（2）第一风诱导，（3）第二风诱导和（4）雾化。对于无层流湍流的低温液体流动，应选择在瑞利制度19 内操作的参数（即， <img alt="Equation 25" src="/files/ftp_upload/61130/61130eq25v2.jpg">）。在这种状态体柱将保持连续的光滑表面，直到所谓的完整长度，估计如下20： <img alt="Equation 26" src="/files/ftp_upload/61130/61130eq26v2.jpg">
图 3 总结了在 60 psig 和 17 K 下运行的 5 μm 直径圆柱形低温氢射流的不同流体参数。为了保持更长距离的连续射流，液体必须冷却到足够接近液固相变的位置（图4），以便在射流在真空中传播后发生的蒸发冷却在瑞利破碎开始之前凝固射流3,21。

<table border="0" cellpadding="0" cellspacing="0" style="width:1149px;" width="1148">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Cryogenic apron</td>
			<td style="width:182px;">Tempshield</td>
			<td style="width:123px;">Cryo-apron</td>
			<td style="width:626px;">Core body protection from cryogenic liquids</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Cryogenic face shield</td>
			<td style="width:182px;">3M</td>
			<td style="width:123px;">82783-00000</td>
			<td style="width:626px;">ANSI Z87.1 rated for full face protection from cryogenic liquids</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Cryogenic gloves</td>
			<td style="width:182px;">Tempshield</td>
			<td style="width:123px;">Cryo-gloves MA</td>
			<td style="width:626px;">Hand protection from cryogenic liquids</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Cryogenic source components</td>
			<td style="width:182px;">SLAC National Accelerator Laboratory</td>
			<td style="width:123px;">Custom</td>
			<td style="width:626px;">Components are made of Oxygen-free Copper (OFC) to maximize thermal conductivity at cryogenic temperatures.</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Cryostat and transfer line</td>
			<td style="width:182px;">Advanced Research Systems</td>
			<td style="width:123px;">LT-3B</td>
			<td style="width:626px;">Available in custom lengths up to 1250 mm for compatibility with existing vacuum vessels. Transfer line length and style can be selected based on system or laboratory space constraints.</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Cylindrical apertures</td>
			<td style="width:182px;">SPI Supplies</td>
			<td style="width:123px;">P2005-AB</td>
			<td style="width:626px;">Commercial cylindrical apertures can be purchased individually</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Electronic-grade isopropanol</td>
			<td style="width:182px;">Sigma Aldrich</td>
			<td style="width:123px;">733458-4L</td>
			<td>99.999%, minimal particulates/trace metals, dries residue free</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Flammable gas regulator</td>
			<td style="width:182px;">Matheson</td>
			<td style="width:123px;">M3816A-350</td>
			<td style="width:626px;">Pressure control of sample gas (e.g. hydrogen, deuterium)</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Indium</td>
			<td style="width:182px;">Indium Corporation</td>
			<td style="width:123px;">Custom</td>
			<td>99.99%, 50-75&#181;m thick, for thermal and liquid seals in cryogenic source</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Jet catcher system</td>
			<td style="width:182px;">SLAC National Accelerator Laboratory</td>
			<td style="width:123px;">Custom</td>
			<td style="width:626px;">Consists of skimmer, vacuum hardware and feedthroughs, vacuum gauge, roots vacuum pump</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Laboratory-grade acetone</td>
			<td style="width:182px;">Sigma Aldrich</td>
			<td style="width:123px;">179973-4L</td>
			<td style="width:626px;">Used to remove grease and photoresist from components. Purity and grade not critical since final cleaning will use electronic-grade isopropanol</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Leak detector</td>
			<td style="width:182px;">Matheson</td>
			<td style="width:123px;">SEQ8067</td>
			<td style="width:626px;">To ensure jet apertures have sealed before pumping down</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Liquid helium</td>
			<td style="width:182px;">Airgas</td>
			<td style="width:123px;">HE 100LT</td>
			<td>Top-loading dewar, Consumption depends on cryostat, source dimensions, and total gas flow. Typically 3-5 L/h.</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Liquid nitrogen</td>
			<td style="width:182px;">Airgas</td>
			<td style="width:123px;">NI 160LT22</td>
			<td>Total cold trap volume 4 L, consumption approximately 2L/h during jet operation</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">LN dewar flask (4 L)</td>
			<td style="width:182px;">ThermoFisher Scientific</td>
			<td style="width:123px;">4150-4000</td>
			<td style="width:626px;">For the liquid nitrogen cold trap</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">LN transfer hose</td>
			<td style="width:182px;">Cryofab</td>
			<td style="width:123px;">CFUL series</td>
			<td style="width:626px;">Uninsulated cryogenic hose with a phase separator to transfer LN from storage dewar to LN dewar flask for the cold trap</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Manual XY manipulator</td>
			<td style="width:182px;">Pfeiffer Vacuum</td>
			<td style="width:123px;">420MXY100-25</td>
			<td style="width:626px;">Course adjustment (+/- 12.5 mm) of cryogenic source.&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Manual Z manipulator</td>
			<td style="width:182px;">McAllister Technical Services</td>
			<td style="width:123px;">ZA12</td>
			<td style="width:626px;">Course adjustment of cryostat length for interchangeability on different vacuum vessels. Additionally, retracting cryogenic source from interaction point.</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Mass flow controller</td>
			<td style="width:182px;">MKS Instruments</td>
			<td style="width:123px;">P9B, GM50A</td>
			<td style="width:626px;">To control and monitor gas flow</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Planar apertures</td>
			<td style="width:182px;">Norcada</td>
			<td style="width:123px;">Custom</td>
			<td style="width:626px;">Custom nanofabrication of planar apertures</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Positioning actuators</td>
			<td style="width:182px;">Newport</td>
			<td style="width:123px;">LTAHLPPV6, 8303-V</td>
			<td style="width:626px;">High-precision (&#60;2&#181;m), motorized jet positioning</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Rotation stage</td>
			<td style="width:182px;">McAllister Technical Services</td>
			<td style="width:123px;">DPRF600</td>
			<td style="width:626px;">Precision alignment of jet orientation</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:219px;">Safety glasses</td>
			<td style="width:182px;">3M</td>
			<td style="width:123px;">S1101SGAF</td>
			<td style="width:626px;">ANSI Z87.1 rated for work with compressed gases</td>
		</tr>
	</tbody>
</table>

cryogenic liquid jets for high repetition rate discovery science

该协议提供了连续微米级低温圆柱形和平面液体射流操作的详细程序。当按此处所述操作时，射流表现出厘米的高层压和稳定性。在瑞利状态下成功运行低温液体射流需要对低温下的流体动力学和热力学有基本的了解。提供了理论计算和典型经验值作为设计可比系统的指南。该报告确定了低温源组装过程中的清洁度和液化后低温源温度稳定性的重要性。该系统可用于高重复率激光驱动的质子加速，有望应用于质子治疗。其他应用包括实验室天体物理学、材料科学和下一代粒子加速器。

在步骤5.4之后，使用高放大倍率阴影图来评估射流操作期间的层流度，定位抖动和长期稳定性。使用脉冲亚纳秒照明来记录射流的瞬时图像至关重要，这样射流运动（H2 为 ~0.1 μm/ns）不会模糊表面不规则或湍流。2 x 20 μm 2 H 2、4 x 12 μm 2 H 2 和 4 x 20 μm 2 D 2 射流的样品图像如图 5 所示。
额外的高放大倍率成像系统用于在太空中精确定位低温液体射流。为简单起见，成像系统旨在提供喷气式飞机的正面和侧面视图。评估射流稳定性并确定平面射流的方向尤为重要。图6显示了在数小时内的单次测试中对2 x 20 μm 2 H2的空间抖动作为与孔径距离的函数关系的研究。图6A中每个数据点的1σ定位抖动是根据以10 Hz记录的49张图像计算得出的。在这里，射流位置是相对于固定参考位置确定的。图6B以23 mm处射流位置的归一化直方图为例。更详细的研究可以在Obst等人中找到。5. 平均而言，空间抖动在远离喷嘴的地方线性增加。
4 x 20 μm2 低温氘射流在液化和射流操作（根据第5节）期间的典型系统可观察量如图 7所示。仔细监控温度、流量、样品背衬压力和真空压力，使操作员能够快速识别任何异常情况并做出相应的反应。例如，如果射流离开捕集器，由虚线框指示，真空室和前线压力显着增加。然后需要额外的冷却功率来维持设定温度。
一旦稳定下来，所有可观察物都应该是恒定的，振荡最小。任何长期漂移都表明存在问题（例如，泄漏、气体污染、真空系统性能下降、捕集器中的定位漂移）。孔径的选择强烈决定了瑞利状态下喷气式飞机的运行参数。一旦确定了给定气体和孔径类型的最佳参数，所得射流就具有高度可重复性;但是，光圈中的任何微小偏差都需要从先前确定的值开始重新优化。典型运行参数总结于 表1。
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61130/61130fig1.jpg"> 图 1：典型低温液体射流输送平台的 P&ID 图。描绘了样品气体、真空和低温子系统。真空室、涡轮分子泵前线和集射流器前线压力分别用真空计 V1、V2 和 V3 监测。低温恒温器温度使用P-I-D温度控制器主动调节。<a href="https://www.jove.com/files/ftp_upload/61130/61130fig1large.jpg" target="_blank">请点击此处查看此图的大图。</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61130/61130fig2.jpg"> 图 2：低温源组件的三维分解图。铟密封件安装在冷手指和源体、源体和法兰以及源法兰和孔径之间。<a href="https://www.jove.com/files/ftp_upload/61130/61130fig2large.jpg" target="_blank">请点击此处查看此图的大图。</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61130/61130fig3.jpg"> 图 3：流体动力学参数摘要。假设在 60 psig 和 17 K 下运行的 ø5 μm 圆柱形低温氢射流，则提供了参数。 密度、粘度和表面张力的值来自 NIST。15. <a href="https://www.jove.com/files/ftp_upload/61130/61130fig3large.jpg" target="_blank">请点击此处查看此图的大图。</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61130/61130fig4.jpg"> 图 4： 低温下的氢状态方程15. 临界点和三相点分别由蓝色和橙色填充圆圈表示。射流操作遵循等压线通过气液相变。射流通过真空室中的蒸发冷却凝固。灰色框表示背衬压力（40-90 psia）和温度（17-20 K）的范围，扫描这些范围以优化ø5 μm圆柱形低温氢射流的稳定性。 <a href="https://www.jove.com/files/ftp_upload/61130/61130fig4large.jpg" target="_blank">请点击此处查看此图的大图。</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/61130/61130fig5.jpg"> 图 5：使用 10 ps/1057 nm 波长激光的无湍流层流低温液体射流的代表性 20 倍放大阴影图。（A） 孔径 = 2 x 20 μm 2， 气体 = H2， T = 15.8 K， P = 188 psig。（二） 孔径 = 4 x 12 μm 2， 气体 = H 2， T = 17.2 K， P = 80 psig.（C） 孔径 = 4 x 20 μm 2，气体：D2，T = 20 K，P = 141 psig。<a href="https://www.jove.com/files/ftp_upload/61130/61130fig5large.jpg" target="_blank">请点击此处查看此图的大图。</a> 
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/61130/61130fig6.jpg"> 图 6：2 x 20 μm2 低温氢气射流的射流位置稳定性。 参数为 18 K、60 psig 和 Re <img alt="Equation 27" src="/files/ftp_upload/61130/61130eq27v2.jpg" style="font-size: 14px;"> 1887。（A） 定位抖动与光圈距离的函数关系。纵向（横向）抖动对应于平行于矩形板的短（长）轴的运动。（B） 射流位置的归一化直方图，以确定距离喷嘴 23 mm 的横向抖动 （σ = 5.5 μm） 和纵向抖动 （σ = 8.5 μm）。<a href="https://www.jove.com/files/ftp_upload/61130/61130fig6large.jpg" target="_blank">请点击此处查看此图的大图。</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/61130/61130fig7.jpg"> 图 7： 低温射流操作期间的代表性流量和压力。（A）左：样气流量，右：样气背压随时间的函数关系。真空室压力的半对数图（V1; B）、涡轮分子泵前线压力（V2; C）和喷射捕集器压力（V3; D）作为时间的函数。带圆圈的数字标识在协议第 5 节期间观察到的系统变化。 <a href="https://www.jove.com/files/ftp_upload/61130/61130fig7large.jpg" target="_blank">请点击此处查看此图的大图。</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always"><tbody><tr><td>样气</td>
			<td>孔径</td>
			<td>温度 （K）</td>
			<td>压力（磅/平方英寸）</td>
			<td>流量（sccm）</td>
		</tr><tr><td>氢</td>
			<td>直径5 μm 圆柱形</td>
			<td>17</td>
			<td>60</td>
			<td>150</td>
		</tr><tr><td>50%氢，50%氘</td>
			<td>直径5 μm 圆柱形</td>
			<td>20</td>
			<td>30, 30</td>
			<td>130</td>
		</tr><tr><td>氘</td>
			<td>直径5 μm 圆柱形</td>
			<td>22</td>
			<td>75</td>
			<td>80</td>
		</tr><tr><td>氢</td>
			<td>1 微米 x 20 微米平面</td>
			<td>18</td>
			<td>182</td>
			<td>150</td>
		</tr><tr><td>氢</td>
			<td>2 微米 x 20 微米平面</td>
			<td>18</td>
			<td>218</td>
			<td>236</td>
		</tr><tr><td>氢</td>
			<td>4 微米 x 20 微米平面</td>
			<td>17.5</td>
			<td>140</td>
			<td>414</td>
		</tr><tr><td>氘</td>
			<td>4 微米 x 20 微米平面</td>
			<td>20.5</td>
			<td>117</td>
			<td>267</td>
		</tr><tr><td>氩</td>
			<td>直径5 μm 圆柱形</td>
			<td>90</td>
			<td>50</td>
			<td>18.5</td>
		</tr><tr><td>甲烷</td>
			<td>直径5 μm 圆柱形</td>
			<td>100</td>
			<td>75</td>
			<td>46</td>
		</tr></tbody></table>表 1：示例射流操作条件。

Watch this Scientific Journal Video about Cryogenic Liquid Jets for High Repetition Rate Discovery Science at JoVE.com

Cryogenic Liquid Jets for High Repetition Rate Discovery Science

该协议介绍了微米级圆柱形和平面低温液体射流的操作和原理。到目前为止，该系统已被用作激光等离子体实验中的高重复率目标。预期的跨学科应用范围从实验室天体物理学到材料科学，最终是下一代粒子加速器。

用于高重复率发现科学的低温液体射流

This protocol presents a detailed procedure for the operation of continuous, micron-sized cryogenic cylindrical and planar liquid jets. When operated as ...

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2.8K 次观看.  SLAC National Accelerator Laboratory. 该协议介绍了微米级圆柱形和平面低温液体射流的操作和原理。到目前为止，该系统已被用作激光等离子体实验中的高重复率目标。预期的跨学科应用范围从实验室天体物理学到材料科学，最终是下一代粒子加速器。

视频: Cryogenic Liquid Jets for High Repetition Rate Discovery Science

Synthesis and Microdiffraction at Extreme Pressures and Temperatures

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary interiors, design materials with novel properties, understand the mechanical behavior of materials exposed to very high stresses as in explosions or impacts. Synthesis and structural analysis of materials at extreme conditions of pressure and temperature entails remarkable technical challenges. In the laser heated diamond anvil cell (LH-DAC), very high pressure is generated between the tips of two opposing diamond anvils forced against each other; focused infrared laser beams, shined through the diamonds, allow to reach very high temperatures on samples absorbing the laser radiation. When the LH-DAC is installed in a synchrotron beamline that provides extremely brilliant x-ray radiation, the structure of materials under extreme conditions can be probed in situ. LH-DAC samples, although very small, can show highly variable grain size, phase and chemical composition. In order to obtain the high resolution structural analysis and the most comprehensive characterization of a sample, we collect diffraction data in 2D grids and combine powder, single crystal and multigrain diffraction techniques. Representative results obtained in the synthesis of a new iron oxide, Fe4O5 1 will be shown.

The laser heated diamond anvil cell combined with synchrotron micro-diffraction techniques allows researchers to explore the nature and properties of new phases of matter at extreme pressure and temperature (PT) conditions. Heterogeneous samples can be characterized in situ under high pressure by 2D mapping and combined powder, single-crystal and multigrain diffraction approaches.

在极端的压力和温度的合成和Microdiffraction

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary ...

科研

工程学

Visualization of High Speed Liquid Jet Impaction on a Moving Surface

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds between 0 and 25 m/sec) and a spinning disk device (for examining surface speeds between 15 and 100 m/sec). The air cannon linear traverse is a pneumatic energy-powered system that is designed to accelerate a metal rail surface mounted on top of a wooden projectile. A pressurized cylinder fitted with a solenoid valve rapidly releases pressurized air into the barrel, forcing the projectile down the cannon barrel. The projectile travels beneath a spray nozzle, which impinges a liquid jet onto its metal upper surface, and the projectile then hits a stopping mechanism. A camera records the jet impingement, and a pressure transducer records the spray nozzle backpressure. The spinning disk set-up consists of a steel disk that reaches speeds of 500 to 3,000 rpm via a variable frequency drive (VFD) motor. A spray system similar to that of the air cannon generates a liquid jet that impinges onto the spinning disc, and cameras placed at several optical access points record the jet impingement. Video recordings of jet impingement processes are recorded and examined to determine whether the outcome of impingement is splash, splatter, or deposition. The apparatuses are the first that involve the high speed impingement of low-Reynolds-number liquid jets on high speed moving surfaces. In addition to its rail industry applications, the described technique may be used for technical and industrial purposes such as steelmaking and may be relevant to high-speed 3D printing.

Two experimental devices for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device and a spinning disk device. The apparatuses are used to determine optimal approaches to the application of liquid friction modifier (LFM) onto rail tracks for top-of-rail friction control.

高速喷液嵌塞对移动表面的可视化

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds ...

A Simple Dewar/Cryostat for Thermally Equilibrating Samples at Known Temperatures for Accurate Cryogenic Luminescence Measurements

The design and operation of a simple liquid nitrogen Dewar/cryostat apparatus based upon a small fused silica optical Dewar, a thermocouple assembly, and a CCD spectrograph are described. The experiments for which this Dewar/cryostat is designed require fast sample loading, fast sample freezing, fast alignment of the sample, accurate and stable sample temperatures, and small size and portability of the Dewar/cryostat cryogenic unit. When coupled with the fast data acquisition rates of the CCD spectrograph, this Dewar/cryostat is capable of supporting cryogenic luminescence spectroscopic measurements on luminescent samples at a series of known, stable temperatures in the 77-300 K range. A temperature-dependent study of the oxygen quenching of luminescence in a rhodium(III) transition metal complex is presented as an example of the type of investigation possible with this Dewar/cryostat. In the context of this apparatus, a stable temperature for cryogenic spectroscopy means a luminescent sample that is thermally equilibrated with either liquid nitrogen or gaseous nitrogen at a known measureable temperature that does not vary (&#916;T &#60; 0.1 K) during the short time scale (~1-10 sec) of the spectroscopic measurement by the CCD. The Dewar/cryostat works by taking advantage of the positive thermal gradient dT/dh that develops above liquid nitrogen level in the Dewar where h is the height of the sample above the liquid nitrogen level. The slow evaporation of the liquid nitrogen results in a slow increase in h over several hours and a consequent slow increase in the sample temperature T over this time period. A quickly acquired luminescence spectrum effectively catches the sample at a constant, thermally equilibrated temperature.

A simple liquid nitrogen Dewar/cryostat apparatus comprised of a small fused silica optical Dewar, a thermocouple, and a charge-coupled device (CCD) spectrograph are described. The experiments for which this Dewar/cryostat is designed require fast sample loading, freezing, and alignment, accurate and stable sample temperatures, and small size/portability.

一个简单的杜瓦瓶/低温恒温器的热的样品配平在为准确低温发光测量已知温度

The design and operation of a simple liquid nitrogen Dewar/cryostat apparatus based upon a small fused silica optical Dewar, a thermocouple assembly, and ...

A High Performance Impedance-based Platform for Evaporation Rate Detection

This paper describes the method of a novel impedance-based platform for the detection of the evaporation rate. The model compound hyaluronic acid was employed here for demonstration purposes. Multiple evaporation tests on the model compound as a humectant with various concentrations in solutions were conducted for comparison purposes. A conventional weight loss approach is known as the most straightforward, but time-consuming, measurement technique for evaporation rate detection. Yet, a clear disadvantage is that a large volume of sample is required and multiple sample tests cannot be conducted at the same time. For the first time in literature, an electrical impedance sensing chip is successfully applied to a real-time evaporation investigation in a time sharing, continuous and automatic manner. Moreover, as little as 0.5 ml of test samples is required in this impedance-based apparatus, and a large impedance variation is demonstrated among various dilute solutions. The proposed high-sensitivity and fast-response impedance sensing system is found to outperform a conventional weight loss approach in terms of evaporation rate detection.

This paper presents an impedance-based apparatus for evaporation rate detection of solutions. It offers clear advantages over a conventional weight loss approach: a fast response, high-sensitivity detection, a small sample requirement, multiple sample measurements, and easy disassembly for cleaning and reuse purposes.

蒸发速率检测一种基于阻抗高性能平台

This paper describes the method of a novel impedance-based platform for the detection of the evaporation rate. The model compound hyaluronic acid was ...

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90&#176; between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

Here, we present a protocol to trigger an orientational transition of a liquid crystal in response to temperature. Methodologies are described for preparing a sample in order to observe the transition and the detailed transitional evolution.

由界面润湿片的热力学生长触发的液晶中的定向转变

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve ...

Measuring the Densities of Aqueous Glasses at Cryogenic Temperatures

We demonstrate a method for determining the vitreous phase cryogenic temperature densities of aqueous mixtures, and other samples that require rapid cooling, to prepare the desired cryogenic temperature phase. Microliter to picoliter size drops are cooled by projection into a liquid nitrogen-argon (N2-Ar) mixture. The cryogenic temperature phase of the drop is evaluated using a visual assay that correlates with X-ray diffraction measurements. The density of the liquid N2-Ar mixture is adjusted by adding N2 or Ar until the drop becomes neutrally buoyant. The density of this mixture and thus of the drop is determined using a test mass and Archimedes principle. With appropriate care in drop preparation, management of gas above the liquid cryogen mixture to minimize icing, and regular mixing of the cryogenic mixture to prevent density stratification and phase separation, densities accurate to &#60;0.5% of drops as small as 50 pL can readily be determined. Measurements on aqueous cryoprotectant mixtures provide insight into cryoprotectant action, and provide quantitative data to facilitate thermal contraction matching in biological cryopreservation.

A protocol for determining the vitreous phase densities of micro- to pico-liter size drops of aqueous mixtures at cryogenic temperatures is described.

在低温下测量水性玻璃的密度

We demonstrate a method for determining the vitreous phase cryogenic temperature densities of aqueous mixtures, and other samples that require rapid ...

Detecting the Water-soluble Chloride Distribution of Cement Paste in a High-precision Way

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a high-precision chloride profile. Firstly, paste specimens are molded, cured, and exposed to cyclic wet-dry conditions. Then, powder samples at different specimen depths are grinded when the exposure age is reached. Finally, the water-soluble chloride content is detected using a silver nitrate titration method, and chloride profiles are plotted. The key to improving the accuracy of the chloride distribution along the depth is to exclude the error in the powderization, which is the most critical step for testing the distribution of chloride. Based on the above concept, the grinding method in this protocol can be used to grind powder samples automatically layer by layer from the surface inward, and it should be noted that a very thin grinding thickness (less than 0.5 mm) with a minimum error less than 0.04 mm can be obtained. The chloride profile obtained by this method better reflects the chloride distribution in specimens, which helps researchers to capture the distribution features that are often overlooked. Furthermore, this method can be applied to studies in the field of cement-based materials, which require high chloride distribution accuracy.

A protocol for obtaining a water-soluble chloride profile by using a high precision milling method is presented.

高精度水泥浆水溶氯分布的检测

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a ...

Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due to their potential applications for future device technologies such as sensors and storage. However, conventional approaches, which usually utilize materials containing magnetic metal ions (or radicals), have a major problem: only a few materials have been found to show the coupling phenomena at room temperature. Recently, we proposed a new approach to achieve room-temperature magnetoelectrics. In contrast to conventional approaches, our alternative proposal focuses on a completely different material, a &#34;liquid crystal&#34;, free from magnetic metal ions. In such liquid crystals, a magnetic field can be utilized to control the orientational state of constituent molecules and the corresponding electric polarization through magnetic anisotropy of the molecules; it is an unprecedented mechanism of the magnetoelectric effect. In this context, this paper provides a protocol to measure ferroelectric properties induced by a magnetic field, that is, the direct magnetoelectric effect, in a liquid crystal. With the method detailed here, we successfully detected magnetically-tuned electric polarization in the chiral smectic C phase of a liquid crystal at room temperature. Taken together with the flexibility of constituent molecules, which directly affects the magnetoelectric responses, the introduced method will serve to allow liquid crystal cells to acquire more functions as room-temperature magnetoelectrics and associated optical materials.

In this report, we present a protocol to examine direct magnetoelectric effects, i.e., induction of ferroelectric polarization by applying magnetic fields, in liquid crystals. This protocol provides a unique approach, supported by the softness of liquid crystals, to achieve room-temperature magnetoelectrics.

液晶中磁调谐铁电极化的测量

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due ...

Preparation of Graphene Liquid Cells for the Observation of Lithium-ion Battery Material

In this work, we introduce the preparation of graphene liquid cells (GLCs), encapsulating both electrode materials and organic liquid electrolytes between two graphene sheets, and the facile synthesis of one-dimensional nanostructures using electrospinning. The GLC enables in situ transmission electron microscopy (TEM) for the lithiation dynamics of electrode materials. The in situ GLC-TEM using an electron beam for both imaging and lithiation can utilize not only realistic battery electrolytes, but also the high-resolution imaging of various morphological, phase, and interfacial transitions.

Here, we present a protocol for the fabrication and preparation of a graphene liquid cell for in situ transmission electron microscopy observation, along with a synthesis of electrode materials and electrochemical battery cell tests.

锂离子电池材料用石墨烯液位的制备

In this work, we introduce the preparation of graphene liquid cells (GLCs), encapsulating both electrode materials and organic liquid electrolytes between ...

Determination of Aggregate Surface Morphology at the Interfacial Transition Zone (ITZ)

Here, we present a comprehensive method to illustrate the uneven distribution of the interfacial transition zone (ITZ) around the aggregate and the effect of aggregate surface morphology on the formation of ITZ. First, a model concrete sample is prepared with a spherical ceramic particle in roughly the central part of the cement matrix, acting as a coarse aggregate used in common concrete/mortar. After curing until the designed age, the sample is scanned by X-ray computed tomography to determine the relative location of the ceramic particle inside the cement matrix. Three locations of the ITZ are chosen: above the aggregate, on the side of the aggregate, and below the aggregate. After a series of treatments, the samples are scanned with a SEM-BSE detector. The resultant images were further processed using a digital image processing method (DIP) to obtain quantitative characteristics of the ITZ. The surface morphology is characterized at the pixel level based on the digital image. Thereafter, K-means clustering method is used to illustrate the effect of surface roughness on ITZ formation.

Determination of Aggregate Surface Morphology at the Interfacial Transition Zone ITZ

Hereby, we proposed a protocol to illustrate the effect of aggregate surface morphology on the ITZ microstructure. The SEM-BSE image were quantitatively analyzed to obtain ITZ's porosity gradient via digital image processing and a K-means clustering algorithm was further employed to establish a relationship between porosity gradient and surface roughness.

在界面过渡区（ITZ）的聚合曲面形态测定

Here, we present a comprehensive method to illustrate the uneven distribution of the interfacial transition zone (ITZ) around the aggregate and the effect ...