lindrical coordinate system has the form:</p>
<div class="math notranslate nohighlight">
\[L = -mc ^ 2 (1- \beta ^ 2) ^ {1/2} + \dfrac {e} {c} A_ \phi r \dot \phi.\]</div>
<p>Axial symmetry implies the existence of an integral of motion:</p>
<div class="math notranslate nohighlight">
\[P_ \phi = \gamma mr ^ 2 \dot \phi + \dfrac {e} {c} r A_ \phi = \gamma mr ^ 2 \dot \phi_0.\]</div>
<p>Differentiating by <span class="math notranslate nohighlight">\(z\)</span> we get:</p>
<div class="math notranslate nohighli