This mechanism operates in all EM sources. It originates from the acceleration of electrons in Coulomb collisions with other electrons and with ions and nuclei. It comes from the German, 'brems' for braking, and 'strahlung' for radiation. The most common situation is the emission from a hot gas as the electrons collide with the nuclei, due to their random thermal motions. This is called 'thermal bremsstrahlung'. Bremsstrahlung can also occur when a beam of particles decelerates on encountering an obstacle. "Braking radiation" is the main way very fast charged particles lose energy when traveling through matter. Radiation is also emitted when charged particles are accelerated. In this case, the acceleration is caused by the electromagnetic fields of the atomic nuclei of the medium. These bremsstrahlung photons have a continuous spectrum with a broad peak of intensity, for photons with roughly half the incident electron energy, and are more numerous in directions perpendicular to the electrons' acceleration vector.
X-rays and shorter wavelengths can be easily generated by striking an anode with highly accelerated electrons within a high voltage gradient.
The higher the temperature of the cathode, the more electrons are released. We measure the level of current in milliamperes (mA). Increasing the current increases the number of electrons emitted from the cathode. This, in turn, increases the intensity of the rays produced. See the heated cathode lifter experiment.
Increasing the voltage (in kV), increases the speed of the electrons that strike the target. Higher potential difference settings produce shorter wavelength EM rays.
Doubling the tube current, doubles the quantity of heat produced. Heat production also varies almost directly with varying kVp. It is known that aluminium has got low Bremsstrahlung radiation levels, but there are other ways that it can emit short wavelength radiation.
The efficiency (not intensity) of x-ray & gamma ray production is independent of the hv current. Regardless of what current is selected, the efficiency of x-ray produciton remains constant. The efficiency of x-ray production increases with increasing projectile-electron energy. It may vary from 1% to 70% depending on the potential difference.