With Hirata-san.

Summary: The unwanted conductive path between the F1 LVDT primary coil seems to happen at the level of the F1 Filter, not at the level of the IP.

Yesterday we suspected the conductive path between pins 1 and 6 of the BS F1 LVDT with the chamber were happening at the in-vacuum connector that is plugged to the flange at the IP level. Today I explored this hypothesis.

We removed pins 1 and 6 from the connector case and measured the resistance values directly at the pins: the conductive path was still there, therefore indicating that the problem is at the F1 GAS Filter level. Unfortunately, this means we need, at least, to lift the whole suspension from the chamber to inspect the connector on top of the F1 Filter.

The values of the resistances measured in the morning were:

• Pins 1, 6: 198 Ohm
• Pins 6 and chamber: 10 Ohm.
• Pins 1 and chamber: 202 Ohm.

In the afternoon Hirata-sa confirmed these measurements.

These values suggest that the thread connected to pin 6 is the one directly connected to the chamber. Pin 1 is connected to the chamber indirectly through the coil.

With respect to the stability of the resistance values, they seem stable now. Yesterday we measured MOhms one time but we haven't been able to reproduce the value, so we believe we made a mistake that time.