I’ve sometimes wondered about the obvious. Why not find a suitable underground location or set of locations in which to set off fusion explosions, and tap the resulting heat. And as a bonus we get to keep up to the minute with nuclear weapon research....
Measurement difficulties (and recovery/salvage of the measurement devices) is just one of the “practical” problems that prevent this approach.
A fusion bomb of course is immensely destructive, and produces a wide variety of particles from the instigating explosion (typically a fission bomb), then more debris and partial particles from the compressed secondary bomb (the hydrogen bomb itself), plus “junk” from the Lithium, tritium, and other internals. All of this stuff is being blown out in random directions away from the bomb.
Plus instantaneous heat and light and blast forces - as you noted.
For physics research you need many minutes of observation of specific energy level particles coming from a known direction - then you “sort” through the many images to find the ones that tell you something. (Kind of like colliding two trucks and looking for the pistons and bearings and fragments of engine castings.) If the detectors only have a few microseconds before they themselves are destroyed, then you have very little chance of finding the reaction you need.
You must have controlled high energy reactions in front of the detectors to that, so using fusion bombs will create heat and light, but not (unfortunately) usable research.