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Why is liquid nitrogen less expensive to use than liquid helium for cooling superconductors?

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Figure 1: Specific heat in the normal (Cen) and superconducting (Ces) states of a classic superconductor as a function of absolute temperature. The two functions are identical at the transition temperature (Tc) and above Tc. — superconductivity Figure 1: Specific heat in the normal (C_en) and superconducting (C_es) states of a classic superconductor as a function of absolute temperature. The two functions are identical at the transition temperature (T_c) and above T_c.

Liquid nitrogen is significantly less expensive to use than liquid helium for cooling superconductors because of the temperature requirements of the materials involved.

Conventional superconducting materials, such as niobium-titanium alloys, must be cooled to temperatures near absolute zero—specifically a few degrees above 0 K—to exhibit superconductivity. Achieving and maintaining these extreme temperatures requires the use of liquid helium, which is a costly coolant.12

In contrast, the discovery of high-temperature superconductors (high $T_{c}$ superconductors) in the late 1980s identified materials that lose their electrical resistance at much higher critical temperatures, such as those above 77 K, the boiling point of nitrogen. Because liquid nitrogen is both plentiful and inexpensive, it serves as a much more economical cooling medium for these advanced materials compared to the specialized and expensive requirements of liquid helium.13