Yesterday a leak became evident in the central area: this morning we progressively isolated  the different vacuum chambers and by RGAs and helium leak detector we finally localized the leak in the external vessel of the NI cryotrap. In attached: a picture of the leaking area and a technical drawing of the concerned part: the defect is located on a lateral finger, likely in the edge-welded bellows or in a weld of the finger pipe itself.

The current leak rate is ~1E-5 mbar·l/s, significant but still manageable. The leak could increase over time.

A temporary fix has been implemented using an external sealing combined with external pumping, keeping the area upstream the leak at a pressure below 1 mbar. The two valves before and after the cryotrap (NI_tower/NI_cryotrap and NI_cryotrap/N_tube) were closed during the works and are still kept closed to verify the correct functionality of the fix  .

Next Wed morning at 8h both valves will be opened and the North arm will become available.

In parallel we prepare for a full replacement with new parts, plan to be discussed with the commissioning team.