An ultra-high vacuum is a vacuum with a pressure of under 10-7 mbar. The mean free path of a particle at this pressure is approx. 1 km. Turbomolecular pumps can achieve an ultra-high vacuum if the systems are perfectly sealed and there are no gassing items in the vacuums. Ultra-high vacuums are required for a small number of technical purposes, for example in particle accelerators and systems for semiconductor doping.