Modern battles are fought at close range—a light-second or so—since lasers are big, heavy, slow, and radiate more than half their power into their parent ships as low-quality waste heat. That’s why every conflict since the 2110s has been fought with missiles and k-slugs.
The danger with missiles is that they’re fast and independently targeted. Try shooting them down with a gun of some type and you have a problem: the missile has traveled literally miles before your bullet gets halfway down the barrel.
Particle beam weaponry was once largely considered to be useless. About the best it can do is barf up some bremsstrahlung secondary radiation. Deliciously lethal, sure, but only in a localized area, and certainly not structurally damaging. The engineer-physicists eventually realized, however, that the particle beam is well-suited to defense. And so, the fan was invented.
The fan makes use of an otherwise annoying property of particle beams. When you deflect a stream of charged particles, you’re accelerating it, but the stream still goes basically the same speed afterward (just in a different direction). That extra energy gets dumped in the form of synchrotron radiation, streaming out tangentially in a flood of hard x-rays. So you get a searing fan of radiation, spreading knifelike in a plane.
Nowadays, when the call goes out for point defense, the ship fires up its spinal-mount linear accelerator. Huge flickering electromagnets in the bow deflect the beam semi-randomly, and a decollaminated blast of bit-flipping, electronics-frying radiation cooks the missiles as they reach the terminal guidance phase.
Small wonder the Jovian Trade Union’s radiation hardening expertise is widely-sought.