If we have a cylindrical shell along the z-axis, with current density $\vec j= j_0 \vec e_z$ and small radius $R_i$ and big radius $R_a$. I tried to find the magnetic field inside by using Ampere's law and I got the following:
$$B=\frac{j_0}{2}\left(\rho -\frac{R_i}{\rho}\right)$$ where $\rho$ is the length of the position vector $\vec r$ projected in the xy-plane. This formula is corrent. I also can use the argument of the right hand rule to express my result as a vector : $$\vec B(\vec r)=\frac{j_0}{2}\left(\rho -\frac{R_i}{\rho}\right)\vec e_{\phi}$$.
But If I want to use only the Amper's Law without the right hand rule, how can I find the vector components of the magnetic field?