多孔注入冷冻靶快速降温过程瞬态特性研究

高度均匀光滑的燃料冰层是惯性约束聚变冷冻靶成功点火的物质前提,其制备关键是在靶丸外建立均匀的球形温度场并进行精确控制。本文针对多孔注入冷冻靶系统,建立了三维仿真模型,数值研究了冷冻靶温度场稳态分布与瞬态降温特性,并分析了接触热阻、氦气压力等因素的影响。结果表明：冷臂温度恒定时,靶丸与充气管接触位置为低温区,激光入射口正对处为高温区,最大温差为003 mK;硅臂加热块功率突降后,靶丸表面最大温差在025 s内急剧上升至8788 mK,温度场均匀性显著恶化;与硅爪 套筒完美接触相比,低温胶层的存在可有效改善降温过程中温度场的恶化,但降温响应时间明显增加;1～10 kPa氦气压力范围内,快速降温过程中靶丸温度响应迅速,且最大温差峰值较小,有利于维持靶丸表面的温度均匀性。     

冷冻靶的环境热辐射屏蔽技术研究

通过建立三维柱腔冷冻靶计算模型,研究了外界环境辐射对间接驱动冷冻靶靶丸及燃料冰层温度场的影响。考虑柱腔内部激光入射孔（LEH）膜透光率对柱腔内靶丸和冰层温度场分布的影响,利用COMSOL软件对柱腔冷冻靶温度场进行了数值模拟计算。研究结果表明：受外界辐射影响,靶丸表面温度场呈两极热、赤道冷分布;LEH膜透光率越大,靶丸外表面温差和冰层内表面温差越大。当LEH膜透光率小于1%时,冰层内表面最大温差低于0.1 mK,可满足冰层均化和保持的要求。实验中,通过在LEH膜上镀不同厚度的铝层调控其透光率,并选择LEH膜镀铝层厚度为35 nm的冷冻靶开展了氘氘冷冻均化实验。结果表明：当LEH膜上的镀铝层厚度为35 nm时,冰层的保持能力得到大幅提升。从X射线相衬图像可知,冰层的厚度均匀性约为80.2%,粗糙度约为1.65 μm,平均厚度约为50.5 μm。     

辐射条件下冷冻靶靶丸表面及充气管温度特性数值研究

在惯性约束核聚变冰层均化实验阶段，观测到充气管内冰晶无法保持，从而不能堵管，靶丸直接与高温氘气源连接，无法继续实验。为解决难以堵管的问题，本文建立了三维冷冻靶系统计算模型，研究了辐射条件下屏蔽罩温度、封口膜透射率及铝套筒表面发射率等因素对冷冻靶靶丸表面及充气管沿程温度特性的影响规律。结果表明：改变封口膜透射率能有效降低靶丸与充气管连接处的温度，在本文讨论的边界条件下，封口膜透射率大于0.025时靶丸与充气管连接处温度相对较低，晶核可维持，充气管能被堵管；而改变屏蔽罩温度及铝套筒表面发射率等做法对靶丸与充气管连接处的温度降低作用不明显，充气管无法被堵管。     

冷冻靶降温过程温度场分布及冰层生存时间研究

为在冷冻靶上成功实现惯性约束核聚变点火，需在打靶前将冷冻靶丸内冰层温度降低1.5 K。针对冷冻靶快速降温过程温度场发生突变导致冰层质量恶化的问题，数值研究了快速降温过程中冷冻靶温度场的瞬态特性，并提出了优化降温方案。数值模拟基于Boussinesq假设，通过UDF编程，获得了降温速率的影响规律，并分析比较了不同延迟时间下延迟降温的数值结果。结果表明：降温开始时，最大温差急剧增大但最终趋于稳定；减小降温速率，可有效改善靶丸表面温度的均匀性，延长冰层的生存时间，使降温结束时冰层质量满足要求；具有特定延迟时间的延迟降温能改善靶丸外表面温度的均匀性从而增加冰层的生存时间，且存在最佳延迟时间使冰层的生存时间最长。     

冷冻靶降温过程温度场分布及冰层生存时间研究

为在冷冻靶上成功实现惯性约束核聚变点火,需在打靶前将冷冻靶丸内冰层温度降低1.5 K。针对冷冻靶快速降温过程温度场发生突变导致冰层质量恶化的问题,数值研究了快速降温过程中冷冻靶温度场的瞬态特性,并提出了优化降温方案。数值模拟基于Boussinesq假设,通过UDF编程,获得了降温速率的影响规律,并分析比较了不同延迟时间下延迟降温的数值结果。结果表明:降温开始时,最大温差急剧增大但最终趋于稳定;减小降温速率,可有效改善靶丸表面温度的均匀性,延长冰层的生存时间,使降温结束时冰层质量满足要求;具有特定延迟时间的延迟降温能改善靶丸外表面温度的均匀性从而增加冰层的生存时间,且存在最佳延迟时间使冰层的生存时间最长。     

TMP结构、材料对冷冻靶温度场的影响

氘氚冰靶的均匀性和表面光滑程度对靶的表现非常重要，高质量的冷冻靶要求靶丸表面最大温差不高于0.1 mK，而影响冷冻靶温度场的因素众多。本文采用计算流体力学软件FLUENT研究了套筒壁厚（0.2、05、0.75、1、1.25、1.5、1.75、2 mm）、材料（AL5052、SS304和高纯铜）以及黑腔结构（单凸环和双凸环）对冷冻靶温度场的影响。计算结果表明:黑腔采用双凸环结构，靶丸表面温差较小；随套筒壁厚的增加，黑腔内气体自然对流强度降低，靶丸表面温度场均匀度提高，靶丸表面温差减小；由于铜具有高的导热系数及比热，选用铜作为套筒材料使得靶丸表面温度更低，温度场更加均匀。将套筒壁厚、材料、黑腔结构综合考虑，发现套筒壁厚为1 mm、材料选用高纯铜、采用黑腔结构双凸环设计时靶丸表面温度场均匀性最好。     

冷冻靶制备中温度控制数值模拟

在二维轴对称模型下，以及惯性约束核聚变冷冻靶制备的温度控制过程中，利用计算流体力学程序Fluent，对聚变腔内的温度场变化进行模拟。研究了腔内气体的自然对流效应对冷冻靶温度分布的影响，模拟了通过在冷却环上施加一正弦振荡的温度场来降低冷冻靶内表面粗糙度的过程，给出了动态快速冷冻方法中的靶温度随冷却环温度的变化过程。     

基于温度冲击的冷冻靶氘氘冰层结晶生长行为研究

惯性约束聚变冷冻靶中氘氘（D₂）冰层的质量对聚变实验的成功与否起重要作用。目前文献报道的制备冷冻靶D₂冰层的方法并不具备好的可操作性，且技术、工艺不定型，制约了高质量冰层的形成。因此，本文采用将温度梯度、降温速率和温度冲击相结合的技术实现燃料冰层在靶丸内的均化。通过温度控制以及施加温度冲击可控地形成残留冰，并在残留冰的控制技术基础上，实现了高质量冰层的可控结晶生长。同时，研究了温度控制对靶丸内D₂冰层品质的影响和D₂冰层结晶生长的过程，并应用晶体生长动力学理论分析了D₂冰层结晶生长行为。从背光阴影图像中的D₂冰层亮环可知，D₂冰层均匀度为85.2%、厚度为40.35 μm、内表面粗糙度为2.15 μm。本方法拓宽了超低温下D₂冰籽晶控制、晶体生长技术，为DT冷冻靶中冰层均化打下了坚实基础，并形成了一定的技术储备。     

冷冻靶封装套中辅助热流密度的优化

为研究达到控温要求的冷冻靶封装套辅助加热量,建立了带有屏蔽罩和暴风窗的冷冻靶的二维轴对称模型。考虑封装套外屏蔽罩辐射强度和封装套内填充气体压力对冷冻靶温度场的影响,利用FLUENT软件对冷冻靶温度场进行了数值模拟计算。结果表明：合理选择上、下辅助加热带的热流密度及其差值,可使靶丸外表面最大温差降至0.1 mK以下;辐射强度越强,气体压力越大,靶丸表面最大温差越大,为实现靶丸外表面温度均匀性要求所施加的上、下辅助热流密度的差值就应越大。     

冷却气体对黑腔系统温度场影响数值模拟

为了研究氦氢冷却气体对黑腔系统温度场的影响，采用CFD数值模拟方法，计算了氘氚靶丸外表面最大温差与填充区域的气体流场随气压、氦气含量变化的规律。通过对冷却壁面施加壁温扰动函数，监测了靶丸外表面平均温度、最大温差随时间的波动。研究结果表明：提高氦氢混合气体的填充压力或减小氦气含量，使得黑腔上下部分冷却气体自然对流强度差异增大，导致靶丸外表面温度场均匀性恶化；但降低冷却气体中氦气含量使气体导热系数减小，比热容增大，使得冷却壁温扰动对靶丸外表面温度场均匀性的影响减弱。     

Effects of TMP Structure and Material on Cryogenic Target Temperature Field

The ice layers in the deuterium-tritium capsule must be uniform and smooth enough, and the maximum temperature difference of the target surface is not higher than 0.1 mK for high quality cryogenic target. However, there are many factors affecting the cryogenic target temperature field. In this paper, the effects of sleeve wall thicknesses (0.2, 0.5, 0.75, 1, 1.25, 1.5, 1.75 and 2 mm), materials (AL5052, SS304 and high-purity copper) and hohlraum structures (single convex and double convex) on the cryogenic target temperature field were studied with FLUENT software. The results show that the temperature difference of target surface is small when hohlraum structure is double convex ring. With the increase of sleeve wall thickness, the natural convection intensity of the hohlraum and the temperature difference on the surface of the target decrease. There is a lower temperature and more uniform temperature field around target surface when copper is used as sleeve material, because of its high heat conduction and specific heat. Considering the wall thicknesses, materials and hohlraum structures, the surface temperature field of the target is best when the sleeve adopts high-purity copper with thickness of 1 mm, and the hohlraum structure is double convex ring.     

Mechanical Design and Analysis of an Indirect-drive Cryogenic Target

Cryogenic target based on indirect-drive concept is concerned widely in the inertial confinement fusion field. An indirect-drive cryogenic target is designed to field on the SGIII laser device of China. Capsule and hohlraum design refers to the NIF ignition target Rev5. The target fabrication encounters many engineering issues because of complicated structures and low temperature experimental environment. A tapered capillary is used to feed and support the capsule. And a jacket is designed to solve capillary fixing, gas filling, sealing and other structural issues. Forming a uniform fuel ice-layer on the capsule inner faces withstanding gravity or surface tension effect is a key feature of this cryogenic target. Thermal mechanical package is designed to have the best capacity of controlling temperature gradient across the capsule with a thermally noncontact method. Thermal analyses conclude the best interface conductance arguments and jacket material for the TMP design. Besides, structural reliability of the target after cooling is conservatively analyzed with an optimized model.     

Numerical Analysis of the Effect of Infrared Radiation on Cryogenic Inertial Confinement Fusion Targets

The present work applies the finite element method to calculate the maximum allowable time that cryogenic inertial confinement fusion (ICF) targets can be exposed to infrared radiation (IR). Hence, a 3-D numerical model integrated with discrete coordinate radiation model was developed to investigate the influence of transmittance of the laser entrance holes (LEHs) and boundary conditions on the temperature field distribution and the maximum DT layer deterioration time for CH, Be, and diamond capsules. Our study shows that introducing such a radiation model can accurately obtain more detailed spatial and temporal distribution information in the ICF targets. The simulation results demonstrate that the Be and diamond capsules provided much better temperature field homogenization than the CH capsule under equivalent boundary conditions, but the CH capsule was heated more by IR radiation than the Be and diamond. In addition, the maximum DT layer deterioration time was significantly increased to 3 s when decreasing the transmittance of the LEH from 0.2 to 0.01. However, either reducing the capsule IR absorption or increasing the inner hohlraum IR absorption demonstrated no conclusive increase in the maximum DT layer deterioration time. These results are expected to provide useful parameters in the design of cryogenic targets and shroud systems.     

Numerical Investigation on Temperature Characteristic of Capsule Surface and Filling Tube of Cryogenic Target under Radiation Condition

During the ice-laying period, a phenomenon is observed that the ice crystal could not be maintained in the filling tube, which results in the direct connection between the capsule and the deuterium source at high temperature. In this paper, a 3D cryogenic target model was established to study the influence of several factors on the temperature along capsule surface and filling tube. The results show that changing the transmittance of the sealing film can effectively solve the problem of being unable to block the filling tube, while changing the shield temperature and the surface emissivity of the aluminum enclosure has no obvious effect on that problem. It is found that the crystal can be maintained in the filling tube under the boundary conditions discussed in this paper with the transmittance of the sealing film greater than 0.025.