magnetic code.sagews

BrMax = 720
MaxLW = 0.63

B = 0.00525
z = 82.67

D = var('D')
R = MaxLW/(2*D)

f = (BrMax/2)*((D+z)/sqrt(R^2+ (D+z)^2) - z/sqrt(R^2+z^2)) - B

plot(f)
find_root(f,0,1)

0.009714958490076983