Electrical Engineering ⇒ Topic : Post-Deflection Acceleration (PDA)

Post-Deflection Acceleration (PDA)

The fourth region is the post-deflection region where the electron beam is accelerated towards the screen in a straight line.

In mono accelerator tubes, the acceleration is given by the anode voltage V,. The brightness given by this voltage is sufficient for low bandwidth tubes up to 10 MHz.

For higher bandwidths, speed of response has to be greater for which velocity of the beam must be very high, otherwise the illumination will be insufficient. For high velocity and good glow of the screen, the kinetic energy must be high which requires high anode potential ( v = √2eV/m ). A high anode potential reduces sensitivity which is inversely proportional. This limits the increase of anode potential which is less than 4 kV in the electrostatic deflection for high sensitivity. To overcome this problem, a post-deflection accelerating potential of 10 kV is applied to make it independent of sensitivity. The sensitivity is of the order of 5 to 50 V/cm.Beam brightness at fast deflection rates is also called writing speed