If they do attach to the inner wall to accumulate then perhaps there can be more electrons that cannot easily attach due to the inner wall already having accumulated electrons. Which also due to the inner wall having a negative charge can perhaps repel each electron as well.

Also perhaps a material that can repel magnetism maybe like a diamagnetic material maybe like a superconductor or something else like pyrolytic graphite or bismuth can repel each electron’s electromagnetism in turn repelling each electron. This maybe can prevent each electron from colliding with the inner wall.