We had some diodes at SSCL that were disks about 3" in diameter by maybe 3/8 thick. They were there to shunt the back EMF from the magnet strings into the dump buses. The buses were 1" or bigger copper pipe parallel to the magnets with 18" vertical standpipes every 50 feet or so. The pipes were filled with water. Which was expected to boil out if there was a quench.
4.6MJ per magnet, 5 magnets per cell. Energy had to go somewhere. Preferably without destroying anything.