2.5 The miniSNO detector and test facility

Q.R. Ahmad, J.C. Beck, R. Meijer Drees, M.A. Howe, K.T. Lesko,^* M.E. Moorhead,^* A.W. Myers, T.D. Van Wechel and J.F. Wilkerson

Last year, work began at NPL on a facility for software and hardware testing related to research on the Sudbury Neutrino Observatory (SNO). Construction of the facility was completed during the past year, and it is now providing valuable support for the commissioning and operation of the SNO detector.

The key component of the facility is a detector dubbed 'miniSNO' (Fig. 2.5-1). It was designed to be constructed quickly and at low cost from spare equipment and phototubes from the SNO detector. The detector is roughly spherical, with an inner diameter of 7 feet. It is capable of holding 128 SNO phototubes, though at the moment only 90 phototubes are available for use in the detector (Fig. 2.5-2). There are currently 42 channels of SNO prototype Front End Card (pFEC) electronics being used to read out the 42 phototubes of the equatorial panels of miniSNO. The miniSNO detector sits in an 18'x14' room capable of holding water to a depth of 12 feet. It was formerly used for neutron shielding of a detector room near the old NPL cyclotron. The water room has been coated with a black sealant, which gives us the option of filling the room and using miniSNO as a true water Cerenkov detector. The adjacent detector room has been converted to a laboratory for the SNO DAQ development and testing as well as maintenance of miniSNO.

The miniSNO test facility is useful to SNO in a number of ways:

1. Since miniSNO uses SNO hardware and produces SNO-format data, taking data with miniSNO allows us to more effectively develop data acquisition software for SNO.
2. MiniSNO is being used to develop and refine procedures, such as electronics calibration and detector monitoring, that will be used in the SNO detector.
3. MiniSNO's ease of access provides a place to test some hardware installation and use before it is attempted in the more restrictive underground environment of SNO.
4. Calibration sources for SNO can be tested with miniSNO .

Recently, miniSNO has been acquiring SNO-format data using a variety of light sources and triggers. Acquisition and analysis of this data has been invaluable for debugging software and better understanding hardware/software interactions. In the near future, NPL will be the site of many SNO Commissioning and Turn-on (CAT) preparations, including a test assembly of the SNO data acquisition system. The availability of the NPL test facility and the miniSNO detector makes possible a more complete preparation for the operation of the SNO detector, and allows us to identify and fix potential problems before they cause delays during underground installation and commissioning of SNO.

Fig. 2.5-1. Top and side views of the Mini-SNO	Fig. 2.5-2. A flattened view of Mini-SNO showing
detector.	the 90 PMT locations (shaded).