What can be the causes of helical motion of a charged particle?
A particle moves along a curved path if it moves in the presence of a magnetic field.
Now, when there is an angular projection, i.e. when the velocity of the particle is at an angle with respect to the magnetic field, then the particle will move in a helical path.
The vertical component (vsin) will be perpendicular to the field and hence will rotate the particle in a circular path. However, the horizontal component (vcos) will move the particle in a straight line path. So, the cumulative motion of the particle is a helix.