[AlexanderHowl]

But you can detonate a pure fusion device without a fissionable element because it is not thermonuclear. As I said, you want to use something else that tritium (50% of the D-D reactions create tritium, which is consumed by secondary fusion reactions and produces the problematic neutrons). You would want either He-3 + He-3 or p + Be-11 (there are proponents of p + Li-7, but around 10% of the reactions instead produce n + Be-7 instead of 4 He, which means that the n produced by the reaction ends up having an energy equivalent to the n from a D + T reaction). Presumably, the device would depend on compression caused by metallic hydrogen detonated by a conventional explosive (Orion is an external explosion, so you cannot use lasers or ion beams with any reasonable chance of success for detonation).