He showed that their charge to mass ratio, e/m, was independent of cathode material.

This effect is due to loose cathode material and usually disappears after a few hours of operation.

In the former example, the pump rate can drop as the cathode material becomes coated.

The cycle then repeats as those electrons enter the cathode material again.

One area of focus is the cathode material.

Next, they set out to modify and optimize the cathode materials.

The purity of cathode materials is crucial for tube lifetime.

Another method is to simply use cathode materials more resistant to erosion.

Development is still required in cathode materials which will resist capacity reduction due to cycling.

CaB is highly conductive, has low work function, and thus can be used as a cathode material.