Model of dust particle

A model describing a dust particle falling into a beam has been developed [7]. The model includes the effect of change of the particle charge due to interaction with the beam. The movement of the particle is guided by forces due to the electric fields of the beam charge and of the image charge at the chamber wall and by gravity. Interestingly the model predicts the signal shortening with increasing beam intensity and lack of dependence of the signal amplitude on the beam intensity (see Figure 7). It also predicts the existence of UFO events with a precursor loss. Such type of events has been observed (see Figure 3 for event with multiple precursors), however in most cases the losses have only one peak.

Figure 7: Model predictions of UFO loss rate for nominal (upper plot, $\rm 3.2\cdot 10^{14}$ protons) and low (bottom plot, $\rm 2.3\cdot 10^{12}$ protons) intensities.