Commonwealth Fusion makes the physics case for its 400 MW reactor
Commonwealth Fusion makes the physics case for its 400 MW reactor
Commonwealth Fusion 为其 400 兆瓦反应堆提供了物理学论证
The scientific community has a plan for achieving fusion power. It involves getting a better understanding of how to control fusion in a tokamak-style reactor using the currently under construction ITER reactor, and then using that knowledge to build DEMO-style plants. But ITER isn’t even expected to see hot plasmas until the middle of the 2030s, by which point solar panels will be so cheap that we’ll probably all be getting them free in our cereal boxes. 科学界有一项实现核聚变能的计划。该计划涉及利用目前正在建设的 ITER（国际热核聚变实验堆）反应堆，更好地了解如何在托卡马克式反应堆中控制核聚变，然后利用这些知识建造 DEMO（示范电站）式工厂。但 ITER 预计要到 2030 年代中期才能看到高温等离子体，到那时太阳能电池板可能已经便宜到我们买麦片都能免费赠送了。
Commonwealth Fusion is a startup that’s basically asking “what if we did that, but now?” Its ITER equivalent, a tokamak called SPARC, is over 70 percent complete and is planned to be operating as soon as next year. The company already has a site and customers for the power-generating follow-on, called ARC. Both of those projects are predicated on using high-temperature superconductors to generate an extremely powerful magnetic field that will allow the company to build a smaller reactor, and thus get things done faster. Commonwealth Fusion 是一家初创公司，它本质上是在问：“如果我们现在就做这件事会怎样？”它的 ITER 等效装置——一台名为 SPARC 的托卡马克装置——已完成超过 70%，计划最早于明年投入运行。该公司已经为其后续的发电项目 ARC 选定了厂址并找到了客户。这两个项目都基于使用高温超导体产生极强磁场，这将使该公司能够建造更小的反应堆，从而更快地完成目标。
Years of running plasmas through tokamaks has given us confidence that the basics of these plans are sound. But there are lots of potential devils in the details (otherwise there’d be little need for experimental reactors). So Commonwealth’s scientists, in collaboration with the academic community, have recently released five peer-reviewed papers that detail its plans for ARC: what our best models tell us now, and what we’ll still need to learn from SPARC to finalize the design of a production fusion plant. 多年来在托卡马克中运行等离子体的经验让我们确信，这些计划的基本原理是合理的。但细节中隐藏着许多潜在的魔鬼（否则就不需要实验性反应堆了）。因此，Commonwealth 的科学家们与学术界合作，最近发表了五篇同行评审论文，详细介绍了其 ARC 计划：我们目前的最佳模型告诉了我们什么，以及我们需要从 SPARC 中学习什么，以最终确定生产型核聚变电站的设计。
The basics of ARC
ARC 的基本原理
The articles are all published in the Journal of Plasma Physics—they’re open access, so you can view them yourself, but they are long (roughly 30–40 page PDFs) and highly technical. What follows is an overview of some of what’s there and a few things that stood out to me as I went through them. 这些文章均发表在《等离子体物理学杂志》（Journal of Plasma Physics）上——它们是开放获取的，因此您可以自行查阅，但这些文章篇幅很长（大约 30-40 页的 PDF），且技术性极强。以下是我在阅读这些文章时总结的概况，以及一些令我印象深刻的要点。
ARC will be a tokamak that hosts fusion between hydrogen’s two heavier isotopes, deuterium and tritium. This reaction results in a helium nucleus and releases a neutron and radiation. The helium transfers heat to the plasma, maintaining the conditions needed for fusion, but it is otherwise a waste product, referred to as “ash” in the fusion context. The neutron and radiation, however, are put to use. Part of that use is simply imparting energy into a blanket of molten salt that surrounds the fusion chamber. That energy, in the form of heat, will be used to drive a turbine that produces the electricity. ARC 将是一台托卡马克装置，用于氢的两种较重同位素——氘和氚——之间的核聚变。该反应产生一个氦核，并释放出一个中子和辐射。氦将热量传递给等离子体，以维持核聚变所需的条件，但在其他方面它是一种废弃产物，在核聚变语境下被称为“灰烬”。然而，中子和辐射则会被利用起来。部分利用方式是将能量传递给环绕聚变室的熔盐毯。这些以热能形式存在的能量将被用于驱动涡轮机发电。
The molten salt includes lithium ions; when one lithium isotope absorbs a neutron, it decays into more helium, plus tritium that can be used as fuel for the reactor. There are isotopes present that will also release additional neutrons, allowing this process to generate sufficient fuel. Overall, the present design of ARC is expected to produce about 1.13 GW of fusion power, with 500 MW of that extracted as electricity. Some of that (100 MW) will be needed to power the plant’s operations, leaving 400 MW to be sent to the grid. 熔盐中含有锂离子；当一种锂同位素吸收中子时，它会衰变成更多的氦，以及可用作反应堆燃料的氚。存在的某些同位素还会释放额外的中子，使该过程能够产生足够的燃料。总体而言，ARC 目前的设计预计可产生约 1.13 吉瓦（GW）的聚变功率，其中 500 兆瓦（MW）作为电力提取。其中一部分（100 兆瓦）将用于维持电厂运行，剩余 400 兆瓦将输送至电网。
The rest of the energy is either kept in the tokamak to maintain the fusion reactions or lost due to inefficiencies in the heat and energy transfer of the system. There’s a lot of uncertainty about these numbers; the 1.13 GW is just the center of a range of potential values running from 900 MW to 1.3 GW, so the 400 MW output may need to be adjusted up or down accordingly. 其余能量要么保留在托卡马克中以维持聚变反应，要么因系统热量和能量传递的低效而损失。这些数字存在很大的不确定性；1.13 吉瓦只是 900 兆瓦到 1.3 吉瓦潜在数值范围的中间值，因此 400 兆瓦的输出功率可能需要相应地向上或向下调整。
Some of that 400 MW comes during periods where fusion is not occurring. The nuclear reactions will occur within 15-minute-long periods that will be interspersed with one minute resets. The resets are meant to be kept short enough that nothing has much of a chance to cool down before it gets heated up again—thermal inertia will let it continue generating power. That will be one of the key differentiators with SPARC, which doesn’t have the heat extraction needed to maintain stable fusion for these long time periods, and so can’t maintain the near constant temperatures needed for reliable power generation. 这 400 兆瓦的部分电力是在核聚变未发生期间产生的。核反应将在 15 分钟的周期内进行，中间穿插 1 分钟的重置时间。重置时间旨在保持足够短，以确保在再次加热之前，各部件没有机会冷却下来——热惯性将使其能够持续发电。这将是它与 SPARC 的关键区别之一，SPARC 不具备维持长时间稳定聚变所需的热量提取能力，因此无法保持可靠发电所需的近乎恒定的温度。
It’s inevitable that parts of the device will be exposed to radiation and perhaps fusion plasma. The inner walls of the reactor will be shielded by tungsten, which will limit erosion by the conditions. Meanwhile, the vacuum vessel is designed to be replaced every one to two years. The papers note that this flexibility will allow them to make some design changes even after ARC is built. To enable this, the whole tokamak is meant to split in half for maintenance. 设备部件不可避免地会暴露在辐射甚至聚变等离子体中。反应堆内壁将由钨屏蔽，这将限制恶劣条件下的侵蚀。同时，真空容器被设计为每 1 到 2 年更换一次。论文指出，这种灵活性将使他们即使在 ARC 建成后也能进行一些设计更改。为了实现这一点，整个托卡马克装置被设计为可以从中间拆开进行维护。
Instabilities
不稳定性
The two big uncertainties in the operations of ARC are long-standing challenges for fusion: how to handle magnetic instabilities, and how to handle the helium ash and material that escapes the magnetic containment. Some of the latter will simply be handled by the resets that happen after every 15 minutes of operation, which will clear the reaction chamber and add fresh fuel. But during operations, this will be handled by what’s called a divertor, an area where the magnetic field lines are shaped to allow some material out of confinement. ARC 运行中的两个巨大不确定性是核聚变领域长期存在的挑战：如何处理磁不稳定性，以及如何处理氦灰烬和逃逸出磁约束的物质。后者的一部分将通过每运行 15 分钟后的重置来处理，这将清理反应室并添加新鲜燃料。但在运行期间，这将由所谓的“偏滤器”（divertor）来处理，这是一个磁力线被塑形以允许部分物质离开约束区域的区域。
“To maximise ARC’s fusion power output while avoiding excessive erosion of the plasma-facing components, we will need to radiatively dissipate most of the power crossing the last-closed flux surface, injecting radiating impurities such as argon or neon to access divertor detachment,” one of the papers says. “Divertor detachment will need to be integrated with a high-performance core plasma, and with efficient impurity pumping to prevent the accumulation of helium ash in the core.” “为了在最大限度提高 ARC 聚变功率输出的同时避免等离子体面对部件的过度侵蚀，我们需要通过辐射耗散掉大部分穿过最后闭合磁通面的功率，注入氩或氖等辐射杂质以实现偏滤器脱离（divertor detachment），”其中一篇论文写道。“偏滤器脱离需要与高性能核心等离子体相结合，并配合高效的杂质泵送，以防止氦灰烬在核心区域积聚。”
The models they use predict that the system will keep enough pressure at the diverter to spit out enough of the helium ash to keep it from interfering with the fusion reactions. But that prediction will need to be tested empirically. Magnetic instabilities can lead to a rapid loss of control of the plasma, potentially leading energetic, charged particles to slam into the reactor walls. The tungsten limits… 他们使用的模型预测，该系统将在偏滤器处保持足够的压力，以排出足够的氦灰烬，从而防止其干扰核聚变反应。但这一预测需要通过实验进行验证。磁不稳定性可能导致等离子体迅速失控，可能导致高能带电粒子撞击反应堆壁。钨限制了……