One part of it is that the plasma sometimes carries a massive current - like, megaamps - that gets dumped into the wall when the plasma contacts it, melting it. This scenario isn't theoretical - it's a big concern when designing and operating tokamaks.
The speed of the particles themselves is also relevant. They're moving rather fast, so they impart a lot of energy when they hit the wall. It doesn't take very many to melt the wall, actually. If some part of the wall sticks out a bit, particles on what are called "banana orbits" will often melt that part off, which isn't good if it's an important part of the wall (e.g. it had been protecting some sensors).
One part of it is that the plasma sometimes carries a massive current - like, megaamps - that gets dumped into the wall when the plasma contacts it, melting it. This scenario isn't theoretical - it's a big concern when designing and operating tokamaks.
The speed of the particles themselves is also relevant. They're moving rather fast, so they impart a lot of energy when they hit the wall. It doesn't take very many to melt the wall, actually. If some part of the wall sticks out a bit, particles on what are called "banana orbits" will often melt that part off, which isn't good if it's an important part of the wall (e.g. it had been protecting some sensors).