低温冷冻靶温度动态特性的数值模拟研究

惯性约束聚变点火成功的关键之一在于靶丸内形成均匀的氘氚冰层,靶丸周围的温度场对冰层质量有很大影响.首先通过实验靶系统实验验证了数值计算模型的可靠性,在此模型的基础上,对低温冷冻靶装置的热物理问题特别是温度动态特性问题展开了数值模拟,重点考察冷环温度波动时,温度传递衰减过程的规律以及各影响因素对于温度传递衰减过程的影响.结果显示:冷环温度一定时,填充气体压力降低、填充气体中氦气比例增大,靶丸表面温度均匀性提高;当冷环温度波动时,温度波动的周期减小、振幅减小、填充气体压力升高、填充气体中氦气比例降低有利于控制靶丸表面温度波动;冷环温度波动的周期适中、振幅减小、填充气体压力降低、填充气体中氦气比例提高有利于改善靶丸表面温度均匀性.研究结果对实验中冷冻靶合理配置各参数实现温度控制具有重要参考价值.

Numerical simulation of dynamic thermal characteristics of cryogenic target

Fusion power offers the prospect of a safe and clean sustainable energy source, and is of increasing importance for meeting the world energy demand and curbing CO₂ emissions. For an indirect-driven inertial confinement cryogenic target, the D-T ice layer inside the capsule should have a uniformity more than 99% and an inner surface roughness less than a root mean square value of 1 μm to avoid Rayleigh-Taylor instabilities. And this highly smooth ice layer required for ignition is considered to be affected by the thermal environment around the fuel capsule. In the present study, a numerical investigation is conducted to examine the static and dynamic characteristics of the thermal environment outside the fuel capsule. Numerical model is proposed and verified by a simplified cryogenic target, and the calculated temperature distribution around the capsule shows to be in good agreement with the experimental data. Based on the established model, the propagation of periodic disturbance of cooling wall temperature in the hohlraum is investigated, and the relations between the temperature disturbance on the cooling wall and the temperature distribution around the capsule surface are obtained. The effects of disturbance amplitude, the disturbance period, and the hohlraum gas composition on the propagation process are investigated separately. The results indicate that for stable cooling temperature, the thermal environment around the capsule shows certain dependence on the gas filled in the hohlraum. The temperature uniformity of the capsule outer surface deteriorates with the increase of fill gas pressure but can be improved by increasing the He content of the filling gas mixture. At an oscillating cooling temperature, the attenuation of amplitude is significant when the periodic disturbance propagates from the cooling rings to the hohlraum and to the capsule surface. For the sine wave form disturbance investigated in the present study, shorter disturbance period results in larger attenuation of the disturbance amplitude. Higher gas pressure leads to smaller amplitude of average temperature on the capsule outer surface. The propagation process of cooling temperature disturbance also demonstrates dependence on the filling gas composition. The higher fraction of H₂ in the He-H₂ mixture helps to attenuate the disturbance amplitude and suppress the propagation of the temperature disturbance. However, the temperature uniformity around the capsule exhibits different characteristics from cooling temperature disturbance. Under the oscillating cooling conditions, moderate period, lower amplitude, lower pressure and higher fraction of He in the He-H₂ mixture help to improve the temperature uniformity around the capsule. The results are of guiding significance for determining the controlling scheme in experiment and further design option for the cryogenic target.