See how much you can store. Note: you’ll have to provide lots and lots of cooling!
This treats the coil as a magnetic energy store, not a power cable. The stored energy is E = ½ L I². Tight winding can raise inductance and help storage, but tighter winding also raises self-field, and that pushes the superconductor toward its field limit and cuts down the current density it can carry. The model below couples those effects instead of pretending they are independent. It also adds a rough cryostat-area-based cooling model so you can see how ugly the wall-plug power and dollar cost get as the thing gets bigger and stupider.
What the model is doing
It estimates a maximum circulating current by solving a coupled rule instead of separate hard caps:
Jc(B) = Jc0 · max(0, 1 − B/Bc2)1.5
and then finds I such that
I = margin · Jc(Bself) · Aturn
with geometry-dependent self-field. More turns tend to increase L, but they also increase the field that chokes the conductor. Solenoids pack tightly and often store more for a given footprint. Toroids confine the field better. Big loose rings look silly but are easy to picture.
How to read the cooling model
The cooling numbers are explicit ballpark assumptions, not sacred truth. The page estimates a cryostat envelope around the coil, computes its outside area, multiplies that by an editable heat-leak-per-area, then turns that cold load into wall power and dollars using editable cryogenic efficiency and cost assumptions.
cold load ≈ area × heat leak
wall power ≈ cold load × W/W
annual electric cost = wall power × hours × $/kWh
What the warnings mean
Any slider marked ⚠ not a direct geometry input is a material or model assumption, not a thing you just dial in by making the wire bigger. Any slider marked ⚠ toy cooling assumption is there so you can change the cryogenic fantasy budget and watch the numbers explode or calm down.