In addition to the other answers, I would like to add that no or very few of the currently operating fusion reactors -- either with magnetic (tokamaks or stellarators) or inertial (laser) confinement fusion -- have any energy-capture system for power generation installed, which further increases the potential difficulty to realize engineering break-even. So there are no experiements which measure the engineering efficiency, simply because there are too many unknowns in what efficiency of such a heat capturing system could be achieved.

With magnetic confinement reactors (which I have some limited with) there are various schemes for breeding tritium for the fuel, which might solve the fuel problem. But on the other hand, it increases the difficulty of how to capture the heat generated from the fusion reaction and converting the heat energy into useful energy. Next, fuel pellets used in magnetic confinement fusion are much simpler (although still cyogenically frozen hydrogen) than in inertial confinemt fucion. The latter of which require increadibly fine-tuned fuel pellets, and the engineering efficieny of latest laser-fusion results should take into account the fact that only a few percent of the shots are successful at the momet, which further degrades the practical engineering efficiency.

In addition to the other answers, I would like to add that no or very few of the currently operating fusion reactors -- either with magnetic (tokamaks or stellarators) or inertial (laser) confinement fusion -- have any energy-capture system for power generation installed, which further increases the potential difficulty to realize engineering break-even. So there are no experiements which measure the engineering efficiency, simply because there are too many unknowns in what efficiency of such a heat capturing system could be achieved.

With magnetic confinement reactors (which I have some limited experience with), there are various schemes for breeding tritium for the fuel, which might solve the fuel problem. On the other hand, it increases the difficulty of how to capture the heat generated from the fusion reaction and converting that heat energy into useful energy. Next, fuel pellets used in magnetic confinement fusion are much simpler (although still cryogenically frozen hydrogen) than that used in inertial confinement fusion - the latter of which requires incredibly fine-tuned fuel pellets. And the engineering efficiency of the latest laser-fusion results should take into account the fact that only a few percent of the shots are successful at the moment, which further degrades the practical engineering efficiency.