一、前言真空的程度是通过一般气体压力来表示的。为了方便起见,真空工程学根据压力范围分成低真空、中真空、高真空。1×10~(-7)乇以下,即10~(-8)乇或10~(-8)乇以下的压力范围叫做超高真空,也有人把10~(-11)乇以下叫做极高真空。超高真空的气体是很稀薄的,气体分子不相互碰撞,运动的平均距离(平均自由程)在1×10~(-8) First, the preface The degree of vacuum is expressed by the general gas pressure. For convenience, vacuum engineering is divided into low vacuum, medium vacuum, high vacuum according to the pressure range. A pressure range of 1 x 10 -7 Torr or less, that is, 10 -8 Torr or 10 -8 Torr or less, is referred to as an ultra-high vacuum, and some people call an extremely high pressure of 10 to -11 Torr vacuum. Ultra-high vacuum gas is very thin, gas molecules do not collide with each other, the average distance traveled (mean free path) in the 1 × 10 -8