Chapter 30 - Nuclear Reactions and Elementary Particles - Learning Path Questions and Exercises - Conceptual Questions - Page 1029: 9

For sustained viable fusion plant, a large number of fusion reactions, hence a high plasma density are required. For the nuclei to get close enough to fuse, high kinetic energies and so very high temperatures are also essential. These requirements are at odds since very high temperatures tend to make the plasma less dense. Conversely, if the higher density is achieved, it would be at a temperature that is not high enough to allow fusion.

For sustained viable fusion plant, a large number of fusion reactions, hence a high plasma density are required. For the nuclei to get close enough to fuse, high kinetic energies and so very high temperatures are also essential. These requirements are at odds since very high temperatures tend to make the plasma less dense. Conversely, if the higher density is achieved, it would be at a temperature that is not high enough to allow fusion.