Problems with lasers
intense lasers needed (e.g. NdYAG 3rd harmonic conversion on nonlinear crystal) have energy conversion efficiency just few percent (2-5% ?). The whole business of nuclear fusion power is about getting net-gain of energy, so loosing 95% right at the beginning seems very stupid.
They are also very heavy, since active medium (Nd ions) are sparsely diluted in heavy inert class/crystal matrix. On top of that there is lot of cooling equipment etc.
Advantages of electron/ion beams?
- On the other hand electron/ion accelerators can easily achieve efficiency 80-90%.
- Also very powerful electron beams can be made quite compact and lightweight (unlike lasers), which is very important for spacecraft propulsion.
- To cause ablation of target or X-ray generation from walls of hohlraum you do not need very fast particles (like hi-end accelerators in CERN) but you are fine with few keV which almost industry-grade machines can produce.
So what's the problem of electron/ion beams?
- One problem with e-beam drivers I read about, is that target becomes negatively charged and e-beam is deflected out or dispersed. But you can easily combine two beams (positive ions and electrons) to avoid that.
- An other problem on Earth is that electron/ion beam systems must operate in vacuum, while lasers can operate in air. Maybe in future applications in spacecraft propulsion the advantage reverse.