Effects of powerful superconducting rings on humans?
I recently came across this paper detailing a plan to use 12 superconducting rings around earth to strengthen our magnetic field. I'm planning on using this same idea for my own worldbuilding.
An advanced civilization is terraforming an Earth sized planet that has no natural magnetosphere. They use 12 superconducting rings to create an artificial one. The NIFS paper I linked to gives me a lot of good information that I need to use this idea, but one part of the paper, on page 10, in particular confused me. It says:
The finite magnetic field generated by a 6.4 MA superconducting ring would necessitate a 2.6 km safety zone adjacent to the cable to assure that the public exposure limit of 5 G is not exceeded.
I'm no physicist, but from what I've gathered G stands for gravitational constant. If I'm not interpreting that incorrectly, then my question is what is the relationship between powerful magnet fields and gravitational constant, and why is there a public exposure limit of 5 G?
Or, more concisely, what effects would a powerful superconducting ring have on a nearby human?
This post was sourced from https://worldbuilding.stackexchange.com/q/82454. It is licensed under CC BY-SA 3.0.
1 answer
I'm reasonably sure that the $5\text{ G}$ there refers to $5$ Gauss. The Gauss is a unit of magnetic flux (named, of course, after Carl Friedrich Gauss). The $5\text{ G}$ figure makes sense, too; it lines up with the recommendations in this Cornell recommended safety guide for public areas (Section 5.3):
All public spaces are limited to less or equal to 5 G for static fields and less than or equal to 1 G for 50/60 Hz fields.
UC San Diego and the IEEE concur, coming up with similar figures for areas of regular exposure without shielding.
Also, let's do the calculations ourselves! The magnetic field outside a wire carrying a current $I$ varies with the distance from the wire, $r$:1 $$B=\frac{\mu_0I}{2\pi r}$$ where $\mu_0$ is the vacuum permeability. If we substitute in the author's $I=6.4\times10^6\text{ Amps}$ and set $r=2.6\times10^3\text{ m}$, we get $B\simeq0.0005\text{ Tesla}=5\text{ Gauss}$ - as the author claims.
High magnetic fields can of course wreak havoc with the heart and potentially other parts of the body, which is why we need to worry about this.
1 I should mention that the equation I used is really just an approximation in the case of a circular wire; it only fully holds in the case of an infinitely long straight wire. However, at such small values of $r$, it works well.
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