Explanation: Maintenance of suitable vacuum is essential so that electrons do not lose their energy. Such a vacuum is achieved and maintained using a combination of rotary pump and diffusion pump. Diffusion pump is attached to the diffusion pump port of the electron beam gun.

Explanation: Diffusion pump is essentially an oil heater. As the oil is heated the oil vapour rushes upward where gradually converging structure is present.

Explanation: The nozzles change the direction of motion of the oil vapour and the oil vapour starts moving downward at a high velocity as jet. This oil is evacuated by a rotary pump via the backing line.

Explanation: High velocity jets of oil vapour coming out of the diffusion pump entrain any air molecules present within the gun. The oil vapour condenses due to the presence of a cooling water jacket around the diffusion pump.

• Power density.

Explanation: EBM the gun is operated in pulse mode. This is achieved by appropriately biasing the biased grid located just after the cathode. Switching pulses are given to the bias grid so as to achieve a pulse duration of as low as 50 μs to as long as 15 ms.

Explanation: Beam current is directly related to the number of electrons emitted by the cathode or available in the beam. Beam current once again can be as low as 200 μamp to 1 amp.

Explanation: Increasing the beam current directly increases the energy per pulse. Similarly, increase in pulse duration also enhances energy per pulse. High-energy pulses (in excess of 100 J/pulse) can machine larger holes on thicker plates.

Explanation: The energy density and power density is governed by energy per pulse duration and spot size. Energy density varies inversely with the spot size, i.e., higher energy density means lower spot size.

Explanation: Spot size, on the other hand is controlled by the degree of focusing achieved by the electromagnetic lenses. A higher energy density, i.e., for lower spot size, the material removal would be faster through the size of the hole would be smaller.