CX1622S Glass Deuterium Thyatron. 35,000v, 5000A pulses for driving laser tubes or microwave circuits.
These tubes are still used because solid state just doesn't work at these power levels. This is a lower power device. The real power thyatrons are ceramic and metal container types.
This is a pentode filled with hydrogen gas. The gas fill allows for quick turnon and turnoff of high current. In operation this would be the circuit would have a very high magnetic pulsing field (safety warning mentions don't come near it with a pacemaker) and also x-rays. Out of circuit, don't drop it.
Love large glass objects.