Why is magnetic field used to deflect electron beam and not an electric field in a television picture tube?

if electric field is used then we have to apply a very high voltage ,or we may require a very long tube.however ,if a magnetic field is used ,even a small field can produce large deflection ,on the other hand ,the required size of the picture tube will be highly reduced .due to this reason,the magnetic field is uesd to deflect the electron beam in T.V. insted of the electric field.