Reactor Engineering

Knowing how to heat a plasma to high temperature and confine it does not, by itself, give you a power plant. Putting a 100-million-degree plasma inside a vessel, holding it up with magnetic fields, extracting its heat, breeding its fuel, and replacing broken parts, these are what make a fusion reactor work as a machine, and that is the business of reactor engineering. This section is a learning roadmap that walks through the major components needed to do this, one at a time.

What you will learn in this section

For a long time, fusion research advanced mainly around a question of physics: how can we confine a plasma? But to build a power plant, you have to answer a harder question one step beyond that. It is an engineering question: how do you build a machine that can withstand such a violent environment?

For example, how do you surround a plasma hotter than the center of the Sun with a vessel that must never melt? One answer is to lift the plasma away from the vessel walls and hold it suspended in an “invisible container” made of magnetic fields. The superconducting coils create this magnetic field, the vacuum vessel is the evacuated room that holds the plasma, and the first wall and divertor take on the places where the plasma inevitably touches the walls. And the blanket recovers the energy produced by fusion as heat while also breeding fuel on its own.

A recommended reading order

The overall picture of the engineering is easier to grasp if you work inward from the outer “container” to the inner “working parts.” We recommend the following order.

1. Vacuum Vessel: The ultra-high-vacuum room that holds the plasma. It is the foundation on which all the other components are mounted.
2. Superconducting Coils: The electromagnets that create the “invisible container” suspending the plasma with magnetic fields.
3. First Wall: The wall that faces the plasma first. It absorbs heat and particles on the front line.
4. Divertor: The component that exhausts the spent helium ash and impurities and takes on the strongest heat flux.
5. Blanket: It recovers heat and converts it to electricity, and breeds the fuel tritium inside the reactor.
6. Heating Systems: The mechanisms that heat the plasma to the temperature needed for fusion.
7. Fuel Cycle: This covers the reactor’s cycle of supplying, recovering, and reusing fuel.

If this is your first time, reading from 1 in order lets you see how the roles of the components connect from the outside inward. If you only want to know about a specific component, you are free to start from whichever page interests you.

Prerequisites so you don’t get stuck

Reactor engineering is a field that takes the properties of the plasma as a given and considers “the machine that supports that plasma.” So if you first get a handle on the underlying topics, each page becomes much easier to understand.

• Basics: The starting point of what fusion is and why ultra-high temperatures are needed.
• Plasma Physics: Here you learn what kind of state the plasma you are dealing with is in.
• Confinement: The idea of confining a plasma with magnetic fields. The components of reactor engineering are the tools that make this happen.

The common challenges reactor engineering takes on

What weighs on every component alike is the harsh environment unique to fusion. The high-energy 14.1 MeV neutrons produced by the D-T reaction slip deep into materials and gradually degrade them. The divertor concentrates a heat flux of up to $10$ to $20$ MW/m², on par with a rocket engine. Because the fuel tritium barely exists in nature, it has to be produced inside the reactor to be self-sufficient. And because of the high-radiation environment, people cannot get close, so broken parts are replaced by robots through remote maintenance. How each component solves these challenges is the highlight of this section.

Related Topics

• Plasma-Facing Materials: Details of the materials used for the first wall and divertor.
• Structural Materials: The structural materials that support the blanket and vacuum vessel.
• ITER: The international project that integrates these components into a real machine.