Two analytical models for computing the pumping speed of a vacuum chamber are derived. The models focus on the vacuum systems used for testing electric propulsion devices. The node model is based on a well-known calculation of the effective pumping speed adjusted by the conductance between the pump and the measurement location. The flux model is derived by balancing particle fluxes at two temperatures: one at the ambient condition, such as the chamber walls; and the second at a cold temperature, indicative of a cryopump surface. The flux model also takes into account gas–wall interaction. The flux model formalism is reduced to solving a linear system of flux transfer matrices for a vacuum chamber section. Simple linear mathematical manipulations allow computing of the pumping speed of complex vacuum chamber shapes. Both models produce a good agreement with the experimentally measured pumping speed for two chambers investigated in this paper.

推导了两个用于计算真空室抽速的分析模型。这些模型着重于用于测试电动推进装置的真空系统。节点模型基于有效抽速的已知计算，该有效抽速由泵和测量位置之间的电导调节。通量模型是通过平衡两种温度下的粒子通量得出的：一种是在环境条件下（例如室壁）；另一种是在室温下。第二个是低温，表示低温泵表面。通量模型还考虑了气壁相互作用。通量模型形式化简化为求解真空室部分的通量传递矩阵的线性系统。简单的线性数学运算就可以计算出复杂真空室形状的抽速。