Re: Why don't magnetic and electrical field lines overlap?

The answer to the first question:
The field lines are visual aids for representing
vector fields such as electric or magnetic field.
By definition the tangent of the field line at
a certain point is the same as the direction of
the vector field at that point. If two field lines
intersect at some point, the vector field at that
point will have two directions, which violates
the definition of a vector field. Therefore field
lines can not intersect by definition, unless at
some singular points where the vector field has
ininite values, for example, at the position of
a point charge.

The answer to the second question:
Static electric force is imposed on an electron
when it is in a static electric field. The direction
of the force is opposite to that of the electric
field. Therefore if we want to focus an electron beam, 
we need a specially designed static electric field
with out-going radial components. When electrons
moving through such a field, they will shift inward
radially. A cylindrical anode with a hole in the
center can serve this purpose. This is also called
an electromagnetic lense and belongs to a research
domain called electron optics, which uses analogy
to optics to study the control of electron beams
in electric or magnetic fields. For further information
I suggest you read the book of A.B. El-Karech and J.C.
El-Karech, "Electron Beams, Lenses and Optics" or some
other books on the same topic.