GERDA Collaboration Meeting at Gran Sasso ========================================== Task Groups 4-8 Feb 3 2005 online minutes by I. Abt --------------- GERDA location in LNGS Matthias Junker ---------------------- Space in hall A plus some space for probably dewars in the tunnel. Superstructure with house with three levels, ground, 1st, 2nd, 3rd level -- 8m long x 4.6m + 1.2m open gallery -- ground lv: all heavy equipment -- 1st level: LVD control room, GERDA control room, lab room -- 2nd level: Ge lab room: length 7.60m [shorter due to staircase] -- 3rd level: in separate units -- floor -- staircase is under the cut-out -- cutout space will provide access -- some lifting device under gallery penthouse -- with cutout -- adjacent to 3rd level water tank with -- platform which supports penthouse Gerda Background Calculation Igor Barabanov ---------------------------- Gamma background [Tl]from inner tank,iron neck and elsewhere: MaGe framework was not used. Look for 2MeV in signal area. For a single detector placed 50cm below the center of the Cu tank: Result: -- Cu tank 1.2 10**-4 cnts/kg/keV -- Fe neck 2. 10**-5 With 252 unsegmented detectors using anti-coincidence the background reduces by a factor 5. Single detector for full construction: -- water tank elements 3 10 **-4 -- open neck 1 10 **-2 ==> open neck is not acceptable. ==> 15cm lead Conclusions: -- 7 cm of lead on the bottom of the water tank -- 6 cm of lead as shoulder on upper part of water `tank -- 15cm of lead on the neck Cryogenic Infrastructure Vasily Kornoukhov ------------------------ Infrastructure is designed to serve 30 m**3 of cryogenic volume. -- thermostating system [2 versions] 1- reservoir with 10m**3 standard purity LN in tunnel -- 300 Watt -- filled once per month 2- refrigerator on 3rd level of superstructure -- 3600 Watt -- filling system -- drainage system -- vacuum super-insulation -- hatch plug / cork open -- The assumption is a gas tight cork. In effect the inner lock is the gas tight volume. -- The standard pressure in the cryostat is 0.2bar. -- The inner 60cm of the neck are free for detector loading. Version 1 of thermoststating is preferred due to -- safety issues -- vibrations from machinery on 3rd level. The reservoir can be smaller, if it is filled more often. If it is small enough it could go into the ground level. A reservoir of pure nitrogen goes into a 3.5m x 6m x 3m height space in the Gallex/GNO area. List of equipment is available. Cryostat Karl-Tasso Knoepfle -------- Re-fill and Cooling System for LN. Another system without a refrigerator[Stirling engine] Several storage vessels are needed plus some pumps. Again a lot of space is needed. Safety has to be considered Possible failures: -- loss of vacuum for superinsolation, i.e. leak in inner vessel 37t LN = 32000 m**3 gas -- inner layer lost -- 7% loss in LN per hour -- okay -- 14h and GERDA is empty -- outer layer lost -- 50% loss in LN per hour -- the water acts as a heater -- the vessel can be emptied in 20 minutes -- both layers lost -- leak in water vessel 660 m**3 H20 All calculations assume an open neck. In reality the neck has to open in case of emergency. Alarms have to be defined. Actions have to be defined. Alarms have levels. At some point the important thing is to avoid explosion. Radon Reduction --------------- Slava Egorov Nemo has a system with a compressor and 2 charcoal columns. There is a description on the web. Air is cooled, radon is removed and the air is reheated. Reduction is about 100. Gerd Heusser For the inflation of the Borexino vessel used synthetic air using pure N2 plus oxygen from bottles. This takes very little maintenance. Discussion The second option -- is technically easier -- needs less space -- produces very clean air However, the cost has to be calculated and the safety issues have to be checked. Perhaps only flow boxes need clean air? Is this feasible. Scintillator Muon Veto Slava Egorov ---------------------- Muons ionization loss is 2 MeV per g/cm**2 When muons get stopped they can produce -- beta decay -- muonic atom --> neutron and gamma emission An example spectrum from muons stopped in copper reveals many lines. In the region of interest there are also several lines, one is exactly at 2040keV. ==> A veto is necessary. A thick plastic scintillator is quite common. Another approach is light collection with fibers. This helps to distinguish between muons and gammas. The assemblies consist of slabs of fibers and Hamamatsu PMT modules. Each one has a cross section of 2m x 0.5m . Total size will be approximately 4m x 4m. It will be on top of the penthouse. The size will be determined by the hole in the water veto system. Lock, Penthouse and Suspensions Iris Abt ------------------------------- We need to base the cooperation between groups on real engineering, i.e. CAD, drawings. Otherwise we will create extra work. It has become clear that the neck of the tank needs a lead screen. Two options were discussed: -- d=1m integrated in bottom of lock thickness = 20cm --> 1.8t -- a screen hanging from the roof minimum version d=2m / thickness =20cm --> 17.3t The version integrated in the lock was chosen. Engineering details depend on neck infrastructure. The neck infrastructure is needed as input for the inner lock design. Safety requirements need to be incorporated. The penthouse has been redesigned according to a former version of the superstructure. It will have to be redone. -- Outer walls will be provided together with superstructure -- Faraday cage is large. -- Electronics area incorporates a control area for testing A first version of the design of the string suspension exists. Strings can be deployed individually. Some positions for the calibration sources were suggested. Munich was asked to define the requirement themselves. MC work will start asap. A string design for the new detector has as a baseline -- 5 Ge detectors -- Cu holders -- Cu/Be wires -- 2 junction boxes serving a maximum of 3 detectors each At the beginning -- 3 Ge detectors -- Cu holders -- Cu/Be wires -- 1 junction box We hope to replace the Cu holders with Ge holders. The original Dyneema fibers were tested: -- strength was only 2/3 of specification -- load of 15kg over 5m -- initial [1/2h] flow: 56mm -- 6mm over 12h -- and this over more than 5 days They are not suitable. Investigation of materials for upper support cable started. The new detectors have a Kapton cable for the pad readout. It goes up to the junction box. From the junction box to the outside world we will have custom made nylon insulated cables. Suspension of old detectors Gerd Heusser --------------------------- The 4 Heidelberg Moscow detectors could go into densely packaged strings kept together with springs. The central core contacts are springs for Ortec and loops for Canberra type detectors. Calculations indicate strict requirements on materials. However, materials are not that well screened so far. In organic materials 40K is a problem. ==> Copper is the better baseline choice for spacers. Nylon or Teflon pads can be used for isolation. A new string design allows for individual detectors to be core contacted. Additional contribution during plenary session Feb.4 Water Tank and Superstructure Alessandro Bettini ----------------------------- Water tank is part of the superstructure designed by external engineering. Material: Carbon Steel plus lining to reduce cost. Seismic shock absorbers are not foreseen as they do not increase safety. The muon veto needs several technical details to be defined. The same is true for the superstructure. A cost estimate for the superstructure exists. The approval of funding is pending. --------- eof ----------------