Find the volume current density that produces the following magnetic field (expressed in cylindrical coordinates):

\[ \vec{B}(\vec{r})=\begin{cases} \frac{\mu_0\,I\,s}{2\pi a^2}\hat{\phi}& s\leq a \\ \frac{\mu_0\,I}{2\pi s}\hat{\phi}& a<s<b \\ 0& s>b \\ \end{cases} \]

What is a physical situation that corresponds to this current density?