Feedthrough Signal Board to Cryostat Seal Design, Testing

The D0 LAr calorimeters are contained in three cylindrical cryostats, symmetrical about the X-Y plain drawn perpendicular to the beam (Z) and through the middle of the center calot:imeter (CC), and terminating in a north and south end calorimeters (ECN, ECS). The center calorimeter holds ca. 5,000, and each end calorimeters holds 3,000, gallons of LAr (BP= ca. 90K) at a nominal pressure of 4/3 atm. The 96 (32 per cryostat) multilayer, G10, signal boards map the signals from the detector to the preamplifiers, while 'feeding them through' the boundary wall between the argon cryostat and the atmosphere. The feedthrough function is accomplished by attaching a hermetic flange to the signal board, and then sealing the flange to an opening in a stainless steel 'signal box', an extension of the cryostat, with a bolted sea. The geometry is arranged to stratify the gas temperature in a 'tower' (port) to keep the box assemblies, nominally, at room temperature. The cryostat design must obey a set of physical constraints that, effectively, require that the circular cross-section be inscribed in a square. All warm 'access ports' are constrained to reside in the upper quadrants; defined as above the equator, outside the circular cross-section, and inside the square. The small diameter (8-inch, 6-inch pipe), vertical axis, ports penetrate the cylindrical, horizontal axis, cryostat shells at large (ca. 45 degree) azimuthal angles to allow a 'reasonable', vertical, heat leak path for the seven (one instrumentation, two HV, four signal) ports required. Each of these ports is 'closed' by a box that serves to provide a surface for the 'feedthroughs', an access panel or panels, and is itself sealed to a cryostat flange. There as many box seals as boxes (seven), eleven panel seals, and (32+80+15) = 127 feedthrough assemblies providing (32*(1200) + 80(8) + 15(61)) = 39,955 individual feedthroughs for each cryostat