Computation of deflection defocusing in CRT electron beams with three dimensional nonlinear analysis of magnetic fields

An analysis is made of the CRT deflection fields using a finite element method (FEM), by both ignoring and considering the nonlinearity in the yoke materials. The results of the linear and nonlinear analyses are compared with the measured values of the fields when the fields are strong enough to deflect the beams to the screen periphery. These computations show that the linear analysis results deviate considerably from the measurements, especially near the yoke. However, the nonlinear analysis results agree well with the measurements. In addition, the paraxial ray theory is applied to calculate the deflection defocusing of CRT beams. The present paraxial ray theory can be used only when either magnetic or electric field exists: the space charge effect of the electron beam is neglected in the analyses. However, the thermal spread of the beam, electron lens aberrations, and the aberrations in deflection fields are all considered.<>