Why do we see a light "circle" in the Thomson Tube?

In the Thomson tube experiment, after the electrons have been accelerated, they enter a glass tube filled with a gas at low pressure. The tube is put between two coils that form a Helmholtz-coil. The electrons are deviated to a circular path due to the magnetic field of the coils.
In the gas, ionisation impact occurs between the accelerated electrons and the gas molecules. The recombination of electrons and ions will then result in light emission which allows us to see an illuminated circle.

My question is: is this emitted light emitted in all directions? If so, why do we see the light as a circle and not just as spread out beams? I understand the electrons are being bent, but why the light emitted from them too?

Thanks in advance.