Re: HTSCs
No, this wasn't a typo. N2/H2 mix would also work and the 77K limit has long since been breached with the latest record for cuprates in the 155K (2015) and 212K in compressed H2S at gigapascal pressures.
The reason for using such a high Tc material is that if the LN2 heats up then it does not quench under the tens of thousands of amps current until it gets about 30K below the Tc.
As the flammability limit for hydrogen is quite high (IIRC >20%) setting the limit lower than this would ensure that a leak would be a minor inconvenience rather than a catastrophe.
Biting the hand that feeds IT
