[LeegleechN]

It's just an absolutely giant construction project. The mass and volume of the construction goes as the cube of the major radius of the reactor. Back of the envelope, SPARC is (6/1.5)^3 = 64 times smaller than ITER. The construction budget for SPARC is ~$500M, so ITER being tens of billions is in line.

[bigyikes]

How do projects like LIGO ever get completed? I’m probably totally naive here, but I thought LIGO is physically larger and has many difficult constraints. The LHC comes to mind as well, and that absolutely dwarfs ITER in physical size. What’s the difference? Dealing with heat output? Superconductors are really hard maybe?

[sbierwagen]

LIGO did take decades to construct, like the LHC. According to LIGO's wikipedia article, it was the most expensive project ever funded by the NSF in 1994.

[neltnerb]

LIGO's size is also deceptive, the legs are kilometers long but the design is an L with the important bit being to vibrationally isolate things, maintain dimensional stability, and maintain vacuum.

ITER is likely bigger in terms of volume of concrete or actual footprint.

[lambdatronics]

Hmm, looks like ITER and LHC both use about the same amount of superconductor: around 500 tons.

[0]https://ieeexplore.ieee.org/document/1018583 [1]https://www.iter.org/mach/Magnets