ght">
\[\phi '- \phi_0' = - \dfrac {e} {pc} \dfrac {A_ \phi} {r}.\]</div>
<p>And in the paraxial approximation:</p>
<div class="math notranslate nohighlight">
\[\phi '- \phi_0' = - \dfrac {e} {pc} B_z (z).\]</div>
<p>From:</p>
<div class="math notranslate nohighlight">
\[\delta \phi = -\int \dfrac {e} {2pc} B_z (z) dz.\]</div>
<p>Then the equations of the trajectory in the given coordinates look like this:</p>
<div class="math notranslate nohighlight">
\[\begin{split}\begin{equation*}
 \begin{cases}
   