As you can see from the above, the introduction of large currents, concommitant loop voltage, and runaways introduces the need for major expensive auxiliary systems to:
- Initiate the currect (central solenoid)
- Carefully measure the current profile on a few ms timescale
- Control the current profile (by rf and microwaves, pellets to modify the density profile)
- Drive the current in "steady state" (neutral beams, rf, microwaves)
- Handle the power from any disruptions (armor)
- Try and prevent disruptions (control parameters, use extra "disruption-prevention" coils)
- Mitigate disruptions
- Stop ELMs (a type of edge disruption)
- Handle runaway electron dumps
None of these systems have anything to do with actually making fusion, and in a reactor, they cause a large amount of the plant's power output to be used to run these systems. Plasma current in a reactor is evil.
Stellarators with only small plasma currents caused by increasing plasma pressure, do not have or need the above systems to operate. That is why I say it is easier and cheaper to engineer a stellarator.