The behavior of the IMC cavity pole frequency and the wide angle scattering has been evaluated as a function of the beam spot position on the IMC terminal mirror.

The beam on the terminal mirror has been displaced by adding an offset on the Automatic Alignment DC quadrant placed in transmission of the IMC cavity to find an optimal position in terms of cavity pole, i.e. the lowest as possible, see logbook entry 31558.

Moreover  a possible correlation between the cavity pole frequency and the wide angle scattering measurement @ 15deg, see logbook entry 31579, has been evaluated.

In Figure 1 e 2 the frequency of the IMC cavity pole is plotted as a function of the vertical and horizontal shift of the beam on the mirror for several horizontal and vertical positions, respectively.

It is visible that the frequency of the pole increases for negative displacements in the vertical direction while there is no significant effect in the horizontal direction.

A similar behavior is visible in figure 3 where the wide angle scattering is plotted as a function of the vertical position of the beam for several horizontal positions. While a completely different behavior can be observed in the horizontal direction (figure 2 compared with figure 4).

For the frequency pole, as we said, there is no dependence on the horizontal position while for the wide angle scattering there is a clear dependence.

The outcomes of the test are not clear jet and further investigations will be performed.