There are many reasons to build a fusion reactor:

It keeps hot-neutron physicists, who you must recruit from among for weapons work, busy.

It provides continual practical challenges to plasma fluid dynamics physicists, who otherwise have great difficulty funding experiments.

It provides cash flow to the (chiefly) military contractors who build the test apparatus.

In this particular case, it lets you conduct tests for thermonuclear weapons concepts paid for out of a different budget.

Any expectation of ever getting useful energy out would be the worst reason, because there will never be one solitary erg of that.

There's a few reasons as I understand it, the power output can be on the same order as a nuclear fission plant. So a single plant taking relatively little real estate can output gigawatts of power to the grid. The fuel is abundant to the point of being practically unlimited. The fuel also needs little in the way of refinement and is not hazardous. A fusion core is naturally fail safe since energy and fuel need to be constantly applied, an accident might destroy a core or plant but not irradiate the surrounding countryside.

> The fuel is abundant to the point of being practically unlimited.

Well, only insofar as we have all the required elements on earth. You still have to go threw a considerably complex and expensive process to make that fuel.

You need to mine lithium and then expose it to plasma to breed tritium.

> A fusion core is naturally fail safe since energy and fuel need to be constantly applied

With a breeder reactor that can be consciously refueled you can also keep its access reactivity very low. And even better, if its fuel is a molten salt the dangerous elements are chemically bound in the fuel. So even if an explosion (terrorist planting C4) would happen in the power plant, and fuel would get spread but the dangerous elements would remain in the molten salt. The dangerous elements are never gaseous and thus never leave the safety boundary of the plant.

A fission reactor in comparsion when hit by C4 can actually release gaseous radioactive material. Just not very much.

So I am not saying fusion reactors are unsafe, but rather then fission reactors can be incredibly as safe.

For myself I would much rather sleep next to a molten salt breeder reactor rather then fusion reactor.

There will never be a commercial fusion reactor power plant.

And if there were, this would not contribute to its development.

Fuel for such a plant (tritium) is practically non-existent. What of it that exists is synthesized at great expense.

It could quite literally save the world in terms of clean energy. I can understand why one would at least try.

100% false.

As with fission, most of the operating costs would have nothing to do with buying fuel. Solar and wind power suffer none of these costs, so fusion, like fission, would be wholly unable to produce power at a price anyone would pay without being forced to.

The fission plants still operating will find themselves increasingly unable to produce power at a price anyone will pay, so will be mothballed long short of their design life.

Generating electricity from sunlight and wind is anything but free. I prefer to pay $0.12/kWh for nuclear energy, as compared to $1.75/kWh for wind or solar, in fact.

If you know you have to lie to make your case, what does that say about your case?

And, who do you imagine you are fooling?

I don’t follow. If anything, the nuclear energy electric rate I quoted is too high.

Regarding Diablo Canyon nuclear plant: “The plant produces electricity for about 6 cents per kWh, less than the average cost of 10.1 cents per kWh that PG&E paid for electricity from other suppliers in 2014.” https://en.m.wikipedia.org/wiki/Diablo_Canyon_Power_Plant#:~....

Fission literally demonstrated that 40 years ago. But we refuse to seriously try that.

The reason I'm personally most excited is interplanetary or even (generation ship) interstellar travel. Fusion fuel is the only practical fuel we know of with enough energy density to provide enough "umph" for long-distance trajectories to be traveled along, at speeds faster than what the Voyager probes had to achieve using multi-year planetary slingshot trajectories.

Fusion rocket information:

https://en.wikipedia.org/wiki/Fusion_rocket

https://www.iter.org/newsline/-/3303

http://www.projectrho.com/public_html/rocket/realdesignsfusi...

A supplement to a fusion power plant: https://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magn...

http://toughsf.blogspot.com/2019/10/the-expanses-epstein-dri...

The only fuels that could achieve better energy density than fusion fuel would be antimatter, or maybe some fanciful sci-fi thing we may discover down the line, such as quark fusion ( https://www.sciencealert.com/new-quark-fusion-releases-signi... ) or subatomic compression ( a concept from fiction that involves packing an immense amount of solid electrons together so tightly that the electrostatic repulsion functions as a compressed spring (perhaps using mutual gravitation almost but not quite strong enough to be a black hole as a way of preventing disastrous spontaneous decompression) ).

Prestige, social status, bragging rights, money (a $billion is table stakes for fusion reactors, so a lot of folks are getting fat cuts), and cool & cushy high-tech careers. Really expensive research has been going on for 50+ years now, with no sign of development - let alone deployment - of actual, practical power reactors.