"If it can be achieved, nuclear fusion would be a massive improvement over fission in that it produces much lower levels of radioactive waste and greenhouse gases, does not require enriched nuclear material that could be used to produce weapons" thermonuclear weapons are fusion yield devices using fission to ignite a fusion fuel. a fusion bomb, or other such weapon is probably closer to production than fusion derived…
Thermonuclear weapons are fusion yield devices using the energetic fission products to confine and compress a fusion fuel so that it can burn.
As soon as the radiation pressure drops below a critical threshold, the fusion reaction ceases immediately. The fusion reaction cannot sustain on its own without this incredible amount of force being applied to it continuously.
This is why we still have not produced commercially-viable pure-fusion power plants. It may still be possible, but if you consider the forces and energies required to create a single-shot weapon that burns its fuel only for fractions of a second, you might start to appreciate the challenge that engineers and scientists have undertaken with the objective of continuously providing fusion power.