主动注入锂用于聚变装置导流器热流的实时控制

IF 1.9 4区 工程技术 Q1 NUCLEAR SCIENCE & TECHNOLOGY
M. Ono, R. Raman
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引用次数: 0

摘要

当局部热通量超过规定的通量极限时,钨PFC表面可能会损坏,这对于可靠的反应堆运行是不可接受的。导流器pfc通常设计为特定的热流密度限制,通常假设平均稳态热流密度为5-10 MW/m2。然而,除了稳态热流外,聚变反应堆导流器pfc还可能经历瞬态热流,如elm和/或其他磁重联事件,这些事件会在导流器pfc上沉积大量的瞬态热流。瞬态导流器的热流密度可能明显大于稳态热流密度,这可能会破坏固体PFC表面。导流器热通量可受到诸如导流器冲击点热通量投影中的不确定性等附加复杂性的影响。此外,还有在非轴对称磁扰动下可能发生的非轴对称功率通量的附加实验观测。液态锂(LL)全氟碳化合物对这种瞬态热通量更有弹性,因为它们可以根据需要蒸发LL,然后丢失的LL可以随后补充。在本文中,我们分析了一个在10 ms内1兆焦耳的瞬态导流器热脉冲的例子。与先前分析的20 MJ热脉冲相比,这是对预期等离子体储存能量的一个小扰动(~ 0.1%)。即使在这种相对温和的热脉冲下,LL表面也会经历~ 100°C的温升。然而,在没有快速冷却机制的情况下,所产生的LL表面加热可能导致LL在瞬态热通量之后继续过度蒸发,从而在约200 ms的时间内显著注入约0.6 mol的Li。这种剂量的锂注射可能导致血浆稀释和性能下降。另一方面,如果优化了主动注入锂的能力,则可以防止LL表面温度升高,从而将随后的锂蒸发到等离子体中的数量减少到被动LL PFC情况的7倍。快速反应球团注入器是主动注入锂的关键工具,它可以在过量的热流到达导流板造成严重损坏之前注入轻杂质球团。一个简单的球团烧蚀模型表明,当球团半径小于0.1 mm,速度为~ 10-20 m/s时,有利于球团沉积。此外,如果可以从私有通量区注入,则颗粒在高热流通量打击点区域的注入效率可高达80%,而从外半径区注入的效率为50%。通过设计一种当烧蚀率达到一定程度时就会破裂的壳-球团,可以进一步提高球团沉积效率。本文提出了一种可能的实现技术,使用电感式颗粒注入器,具有几毫秒的快速时间响应,可以在NSTX-U中进行测试。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Active Lithium Injection for a Real Time Control of the Divertor Heat Flux for Fusion Devices

Active Lithium Injection for a Real Time Control of the Divertor Heat Flux for Fusion Devices

When the local heat flux exceeds specified flux limit, tungsten PFC surfaces can be damaged, which is not acceptable for a reliable reactor operations. The divertor PFCs are typically designed for a specific heat flux limit usually assuming an average steady-state heat flux which is typically 5–10 MW/m2. However, in addition to steady-state heat flux, fusion reactor divertor PFCs could experience transient heat fluxes such as ELMs and/or other magnetic reconnection events which can deposit large transient heat fluxes onto the divertor PFCs. The transient divertor heat flux could be significantly larger than the steady-state heat flux which could damage the solid PFC surfaces. The divertor heat flux can be subjected to additional complications such as the uncertainties in the the divertor strike point heat flux projection. Moreover, there are additional experimental observations of non-axisymmetric power flux which can occur under non-axisymmetric magnetic perturbations. The liquid lithium (LL) PFCs is more resilient against such transient heat fluxes as they could evaporate LL as needed and the lost LL can be then replenished afterward. In this paper, we analyze a case for a transient divertor heat pulse of 1 MJ in 10 ms for a ITER-size reactor. This is a small perturbation (~ 0.1%) to the expected plasma stored energy compared to the previously analyzed case of 20 MJ heat pulse. Even with this relatively modest heat pulse, the LL surface undergoes ~ 100 °C temperature rise. However, the resulting LL surface heating without rapid cooldown mechanism could lead to excessive LL evaporation continuing well after the transient heat flux resulting in a significant Li injection of ~ 0.6 mol in about a 200 ms period. This amount of Li injection could cause plasma dilution and performance degradation. On the other hand, an active Li injection capability if optimized could prevent the LL surface temperature rise and thus reducing subsequent Li evaporation into the plasma by a factor of 7 compared to the passive LL PFC case. A crucial tool of active Li injection is a rapid response pellet injector which could inject light impurity pellets before the excessive heat flux could reach the divertor plate causing serious damage. A simple pellet ablation model suggests a favorable pellet deposition profile for smaller ~ 0.1 mm radius pellet with ~ 10–20 m/s velocity. Moreover, if it is possible to inject from the private flux region, the pellet injection efficiency into the high heat flux strike point region can be as high as 80% compared to ~ 50% for the injection from outer radius region. The pellet deposition efficiency can be further improved by designing a shell-pellet which can burst when a certain ablation fraction is reached. A possible implementation technique using an inductive pellet injector with a rapid time response of a few msec is proposed here which can be tested in NSTX-U.

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来源期刊
Journal of Fusion Energy
Journal of Fusion Energy 工程技术-核科学技术
CiteScore
2.20
自引率
0.00%
发文量
24
审稿时长
2.3 months
期刊介绍: The Journal of Fusion Energy features original research contributions and review papers examining and the development and enhancing the knowledge base of thermonuclear fusion as a potential power source. It is designed to serve as a journal of record for the publication of original research results in fundamental and applied physics, applied science and technological development. The journal publishes qualified papers based on peer reviews. This journal also provides a forum for discussing broader policies and strategies that have played, and will continue to play, a crucial role in fusion programs. In keeping with this theme, readers will find articles covering an array of important matters concerning strategy and program direction.
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