Hydrogen Vessel and Support Structure

The original hydrogen pressure vessel from Gatchina which was used while running with the prototype TPC had to be redesigned for several reasons:

• Since existing Sindrum chambers nr. 3 and 5 will be used as outer electron tracker, the new pressure chamber has to fit inside the inner radius of chamber nr. 3. This requirement limits the outer diameter of the end flanges to 348 mm allowing a free inside diameter of 280 mm.
• The back tracking of electrons from the Sindrum chambers requires thin cylindrical walls of the pressure chamber and a material selection optimized to keep multiple Coulomb scattering as small as possible without sacrifying safety for the operation with vacuum and with a 10 bar hydrogen filling. The optimal and technically feasible choice was found to be a cylindrical Aluminum wall with thickness 2 mm.

  For the future, we will investigate the use of aluminized carbon fibre materials to reduce further multiple Coulomb scattering on the walls.

• The pressure vessel must be bakeable to 150$^o$C due to the high purity requirements.
• All selected materials should be of low outgasing type, e.g. metals or ceramics.
• The beam entrance window (diameter 40 mm) will be chosen as thin as possible to achieve near complete muon beam stopping in the TPC.
• The vessel should be long enough to house the TPC and two muon chambers; it should be adjusted to the geometrical acceptance of the Sindrum chambers.

As a result of these considerations, we have designed a 60 cm long cylindrical vessel of Aluminium metal with 2 mm Alu walls and with stainless steel flanges at the front and back sides.

The vessel will be supported on the back side by a strong steel pipe which is also used for high vacuum pumping. The support will be mounted on a precise slide to move it in and out of the Sindrum chambers for detector maintenance and outbaking purposes.