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By calculating the circular component in Newton’s law equations in combination with Lorentz force, we can obtain that the trajectory for meridional rays in a meridional plane rotating behaves at an angular velocity,
 [4276]
This equation is known as the Larmor frequency that is half the cyclotron frequency of an electron on a circular trajectory. φ is the rotation angle as shown in Figure 4276.
Figure 4276. Schematic illustration of rotationally symmetric magnetic fields and electron lenses.
