QuantumDot wrote: to solve the thrust problem with the focus fusion you just need to add some material in front of the ion beam and let the beam heat and then eject the material, it would basically function like a pulse detonation rocket engine with the FF acting as a ignition source. so there would still be a lot of engineering problems but it would be possible for a single stage craft. using a deep cooling precooler and then the ff to ignite and then when it gets too high use some stored fuel as a rocket and then when in space just use the pure ion beam or when you need more thrust revert it back to a rocket. adding in optical and magnetic refrigeration would reduce the weight add simplify the design and be useful at all stages of the vehicles life.
I think that you violated the law of conservation of energy. If for example a FF pulse imparts 10 Joules of energy then you can’t make it 100 Joules of energy by putting something in the way of the blast unless you put something in the way that explodes (releases additional energy by breaking chemical bonds) when hit with by an ion beam.