Final answer:
An electron beam is generated in a high-vacuum environment to allow electrons to be accelerated without interference and to enable the production of clear and unscattered X-rays when they strike a metal plate.
Step-by-step explanation:
An electron beam is always generated in a high-vacuum environment. When an electron is accelerated in an evacuated tube by a high positive voltage and strikes a metal plate, such as copper, it produces X-rays. The high-vacuum is necessary because it provides an environment free of gas molecules that could interfere with the electron's path or scatter the produced X-rays. Creating electrons with a specified level of energy, as mentioned for electron waves, also implies the need for a vacuum to avoid interactions with other particles.