Scenario for the gas system 1.High cost gas (5 €/l of Xe) 2.High hydrostatic pressure over 7 m height 3.Light and large detectors, no big under- or over-pressures affordable 4.Highly segmented detector (540 chambers)

Solutions Gas recirculation, no gas injection except for compensating for leaks (1) Pressure regulation subdivided into (groups of) sectors (2,3) Capillary gas inlet and two-stage outlet regulation for ensuring uniform flow and overpressure (2,3) Gas regeneration for Xe recuperation (1,4)

2-stage pressure regulation realistic pressure regulation test at point 2: Two vessels at 6 m difference in height, at the plug; Compressor at the surface.

Precise and stable regulation

Filling Flush with CO2 Use membranes to replace CO2 by Xenon 2 days operation (see Trento)

Nitrogen removal Use Cryogenic distillation after run (see Trento and ALICE note)

Schedule Design practically ready –Need to decide on final regulation segmentation PRR in October (following other gas system PRRs) Construction: ?