In an embodiment, a system is provided that includes an electron gun, a focusing system, and a housing. The electron gun can include a cold cathode electron source and an extraction electrode. The focusing system can be configured to focus a beam of electrons extracted from the electron gun to a focal region. The housing can include the electron gun and extend along a housing axis in the direction of the electron beam. The cold cathode source is configured to emit electrons at a first operating pressure that is higher than a second operating pressure at the focal region of the electron beam.

Disclosed is an x-ray tube including a hybrid electron emission source, which uses, as an electron emission source, a cathode including both a field electron emission source and a thermal electron emission source. An x-ray tube includes an electron emission source emitting an electron beam, and a target part including a target material that emits an x-ray as the emitted electron beam collides with the target part, wherein the electron emission source includes a thermal electron emission source and a field electron emission source, and emits the electron beam by selectively using at least one of the thermal electron emission source and the field electron emission source.

Disclosed is an x-ray tube including a hybrid electron emission source, which uses, as an electron emission source, a cathode including both a field electron emission source and a thermal electron emission source. An x-ray tube includes an electron emission source emitting an electron beam, and a target part including a target material that emits an x-ray as the emitted electron beam collides with the target part, wherein the electron emission source includes a thermal electron emission source and a field electron emission source, and emits the electron beam by selectively using at least one of the thermal electron emission source and the field electron emission source.