If someone were to drill into that huge tube, one would see the inner walls densely wound with metal coils. There was not a single gap. Close to the top of the tube, there was even a metal coil that had already been burnt up, slowly falling.
Of course, there were many more structures, complicated beyond the realm of human understanding, which was another matter.
According to the artist friend (who was artistically talented but lived a little poorly due to his enthusiasm for DIY projects), this was called a coil-type electromagnetic gun. The initial speed of the projectile was slow. It relied on a long barrel to provide acceleration. But if the barrel was long enough, the power supply sufficient, and the design perfect, it could launch extremely heavy things at frighteningly high speeds.
It would be theoretically possible to shoot a one-ton mass of iron at the speed of the Third Cosmic Velocity without difficulty.
