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How does a vacuum increase the distance a particle travels before colliding with another particle?

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McLeod gauge; vacuum technology — vacuum technology Diagram of a McLeod gauge.

In the context of vacuum technology, a vacuum increases the distance a particle travels before colliding with another by reducing the number of molecules present in a given volume.1

The average distance a particle moves between collisions is known as the mean free path. In a gas, the mean free path is inversely proportional to the density or pressure of the gas. By lowering the pressure—which effectively removes atmospheric constituents and decreases the number of molecules per unit volume—the likelihood of a particle encountering another is significantly reduced.2341

This extension of the mean free path is essential for various applications, such as particle accelerators, vacuum coating, and television picture tubes, where it is necessary for particles to travel from a source to a target without being deflected by collisions.1