This has largely relegated these devices to experimental, rather than practical purposes, and confining the reaction – the same one that occurs inside the sun or other stars – is at the heart of the issue. Unlike in nuclear fission, where atoms hit each other release energy, a fusion reaction involves heating up a gaseous fuel to the point where the atoms break apart into ions and electrons from the pressure and then the free ions fuse into a heavier nucleus.
The process involves the release of a massive amount of energy, a million times more than a typical chemical reaction, such a burning a fossil fuel, according to McGuire. But to do this you need to be able to hold the gas, which is eventually in a highly energized plasma state, for a protracted period of time at a temperature of hundreds of millions of degrees Fahrenheit.
This generally limits the potential for reactors, even large ones, because of concerns they might fail spectacularly. In the 2014 interview with Aviation Week, McGuire used tokamaks, a magnetic confinement device scientists in the Soviet Union first invented in the 1950s, as an example, stating that they had a low magnetic pressure limit under which they could safely operate.
With McGuire's help, the article succinctly explained, at least in theory, how the CFR was supposed to get around these issues:
If the system works, it’s hard to underscore just how dramatically it could change not just the future of warfare, but the basic nature of human existence. Running on approximately 25 pounds of fuel – a mixture of hydrogen isotopes deuterium and tritium – Lockheed Martin estimated the notional reactor would be able to run for an entire year without stopping. The device would be able to generate a constant 100 megawatts of power during that period.