On the understanding of the pressure bump

The interpretation of the ion-induced pressure bump observed in CERN's Intersecting Storage Ring (ISR) is re-examined. An improved formulation is proposed by combining the time-variation of the number of molecules on the chamber wall with the pressure change. Assuming proper conditions on the molecules contributing to the ion-desorption, the pressure bump can be described with a consistent manner. Unlike a generally accepted view, the pressure is not in stationary conditions during the pressure bump. Usual criterion on the occurrence of the pressure bump is still valid. However, the pressure bump must be understood as a dynamic phenomenon.