A cryogenic current lead is a device that connects a current source located at room temperature with a superconducting element immersed in a cryostat (liquid helium or nitrogen).
Liquid helium
Since the heat flux to the cryoagent occurs mainly through current leads, their efficiency determines the cost of operating a superconducting product, which are expressed in the cost of liquid helium, or in the power of a refrigeration unit. The main task in the development of current leads is to reduce the heat gain to the cryoagent at a given current strength. The heat flux through the current leads has two components. The first is due to the thermal conductivity of the current leads themselves, and the second is the ohmic heat release in them.
Nitrogen
Instead of liquid helium for cooling, you can use a less expensive cryogen - liquid nitrogen, which greatly simplifies the design of the current limiter and reduces its size. The thermal conductivity and electrical resistance of the current leads in this case should be minimal.