[Jon, Jordan, Koji]

Today Jordan reconfigured the vac system to allow pumping of the main volume resume, with Jon and Koji remotely advising. All clear to resume normal IFO activities. However, the vac system is operating in a temporary configuration that will have to be reverted as we locate replacement components. Details below.

Procedure

Since serial readback of the TP2 controller seems to be failing, we reconfigured the system with TP3 now backing for TP1. TP2 was valved off (at V4) and shut down until we can replace its controller.

TP3 has its own problems, however. It was valved off in January after its temperature readback began glitching and spuriously triggering the interlocks [ELOG 15140]. However the problem appears to be limited only one readback (rotation speed, current, voltage are fine) and there is enough redundancy in the pump-dependent interlock conditions to safely connect it to the main volume.

We also discovered that sometime since January, the TP3 dry pump has failed. The foreline pressure had risen to 165 torr. Since the TP2 and TP3 dry pumps are not interchangeable (Agilent vs. Varian), we instead valved in the auxiliary dry pump and disconnected the failed dry pump using a KF blank. This is a temporary arrangement until the permanent dry pump can be repaired. Jordan removed it to replace the tip seals and will test it in the bake lab before reinstalling.

With this configuration in place, we proceeded to pump down the main volume without issue (attachment 1). We monitored the pumpdown for about 45 min., until the pressure had reached ~1E-5 torr and TP3 had been transitioned to standby (low-speed) mode.

Summary of topology changes:

• TP2 valved off and shut down until controller can be replaced
• TP3 temporarily backing for TP1
• Auxiliary dry pump temporarily backing for TP3
• TP3 dry pump has been removed for repairs