Now I know one reason more why I had trouble to see a electron beam. The vacuum was too bad.

I figured out that electron beam disappear if I place a wire with 0.3mm between the rubber plug and the gals wall.

Further I figured out that by changing the spark gap from the anode side to the cathode side I could remove the aluminum strip from the bottom of the glass. Also I changed the screen material from glowing in the dark powder to pure zinc sulfide.