A twystron is a type of microwave-producing vacuum tube most commonly found in high-power radar systems.
The name refers to its construction, which combines a traveling wave tube, or TWT, with a klystron, producing a tw-ystron.
As they pass through the holes, the signal within the resonator causes the electrons to "bunch up", a process known as velocity-modulation.
The device was developed by Albert La Rue and Rodney Rubert in the early 1960s and was quickly adopted by many radar designs in order to improve frequency agility and thereby improve performance against radar jamming systems.
The twystron was generally replaced by the extended interaction klystron and solid state amplifiers.