\propto v^{2}$. The picture below on the right: Measurements of the critical current of symmetric aluminum ring with the radius $r \approx 2 \ \mu m$ [@JETP07J] corroborate the predominant probability of the $n$ state in the interval $(n-0.5) \Phi _{0} < \Phi < (n+0.5) \Phi _{0}$.](Fig5)

According to the canonical definition the gradient operator $\hat{p} = -i\hbar \nabla $ corresponds to the canonical momentum $p = mv + qA$ of a particle with a mass $m$ and a charge $q$ both with $A \neq 0$ and without $A = 0$ magnetic field [@LandauL]. The velocity operator $\hat{v} = (\hat{p} - qA)/m = (-i\hbar \nabla - qA)/m$ [@FeynmanL], in contrast to the momentum operator, depends on the magnetic vector potential $A$. Therefore the velocity of Cooper pair with $q = 2e$ $$\oint_{l}dlv  = \frac{2\pi \hbar }{m}(n-\frac{\Phi }{\Phi_{0}}) \eqno{(2)}$$ cannot be equal zero when the magnetic flux $\Phi = \oint_{l}dl A$ inside the loop $l$ is not divisible by the flux quantum $\Phi _{0} = 2\pi \hbar /q = \pi \hbar /e \approx 20.7 \ Oe \ \mu m^{2}$. The velocity $ldv/dt = -(q/m)d\Phi /dt$ and the persistent current $L _{k}dI _{p}/dt = L _{k}sqn_{s}dv/dt = -d\Phi /dt $ change with 