Glossary

Fusion research is a field where physics, engineering, materials science, and many other disciplines intersect, and it uses a great deal of specialized vocabulary. This glossary organizes the key terms you will want to know when studying fusion, arranged in alphabetical order.

How to Use This Glossary

Each term page begins with a “Simple Definition (High School),” followed by a precise definition at the undergraduate level and above, and then links to the main learning pages. If you are studying fusion for the first time, we recommend starting with the simple definitions of basic terms such as “plasma” and “fusion reaction.” If you already have some background knowledge, use the “Learn More” links on each page to jump to the relevant explanatory page.

Characteristics of Fusion Terminology

The vocabulary of the fusion field has several distinctive features.

First, a large share of the terms originate in plasma physics. Plasma is the star of fusion, and specialized concepts such as “Debye shielding,” “MHD instability,” and the “Lawson criterion” were developed to describe its behavior.

Second, the names of devices and confinement schemes occupy an important place. “Tokamak” comes from a Russian acronym, and “stellarator” derives from the Latin word for “star.” These names reflect the physical characteristics and development history of each device.

In addition, English abbreviations and acronyms are common. International project names such as ITER, NIF, and JT-60SA are almost always referred to by their abbreviations. These are also covered in the glossary as needed.

Alphabetical Index

B

• Blanket - Equipment responsible for heat recovery and tritium breeding

C

• Confinement - Methods for holding high-temperature plasma

D

• Debye Length - The distance over which charge imbalances are shielded
• Disruption - A sudden collapse of the plasma current
• Divertor - An exhaust port that receives heat and particles

F

• Fusion Reaction - The nuclear reaction that powers the stars

H

• H-mode - An operating state in which confinement suddenly improves

I

• Inertial Confinement Fusion - A scheme that implodes fuel with lasers
• ITER - An experimental reactor under construction through international collaboration among seven parties

L

• Lawson Criterion - The condition required for fusion to be achieved

M

• MHD (Magnetohydrodynamics) - A theory that treats plasma as a single fluid

P

• Plasma - The fourth state of matter, essential to fusion
• Plasma Beta - The ratio of plasma pressure to magnetic pressure

S

• Safety Factor - The index q representing how much the magnetic field lines twist
• Stellarator - A twisted magnetic confinement device

T

• Tokamak - A doughnut-shaped magnetic confinement device
• Tritium - An isotope of hydrogen that serves as fusion fuel