Lorentz force. This diagram illustrates the behavior of a charged particle q moving with velocity v in a magnetic field B. The latter is oriented out of the page, as indicated by the dot in the circle. The particle is accelerated by the Lorentz force, with its behavior determined by the formula:
F=qE+qc[v×B]{\displaystyle F=qE+{\frac {q}{c}}\left[v\times B\right]}
where F is the force vector, E is the electrical field, and c is the speed of light. The × symbol represents the mathematical curl operator. The direction of the electron's curved path is determined by the sign of its charge, which modifies the sign of the v × B in the formula above.
Own work using:

Wiedemann, Helmut (14 April 1999)       Particle Accelerator Physics: Basic Principles and Linear Beam Dynamics (2nd ed.), Springer  ISBN:  354064671X.
Jaro.p