1. You need some deuterium loaded metal (palladium, titanium, nickel, ..) as target.
2. Accelerate ions of hydride to the target.
Result: D-D -> 3He + n
This reaction can generate 2.5 MeV and can be boosted significantly.
Temperature must be kept low enough so desoription of the deuterium can't occur.
This will work and will generate significant amount of neutrons.
Why this phenomenon is ignored?
On the other hand, we can start isotopic transmutation to deuterium, tritium, quatrium from hydrogen by electron scattering. And this is more complicated, but not impossible.