Fall 2008


Image of DCS driveEarly in 2008, PSL mechanical engineer Ken Kriesel and CAD specialist Glen Gregerson began design of a detector calibration system (DCS) for the Cryogenic Underground Observatory for Rare Events (CUORE) with Assistant Professor Karsten Heeger and others of the UW-Madison Physics Department.

CUORE is intended to improve measurements of mass of the electron neutrino well beyond current bounds. Paradoxically it will accomplish this by studying neutrino-less double beta decay. It employs 988 tellurium oxide crystals cooled to 0.01 degrees Kelvin for improved sensitivity. The tellurium is about one-third composed of an isotope that will decay, so it both provides the source of decay and makes up part of the detector. The purpose of the DCS is to lower and raise to known positions under independent control 12 strings of 29 weakly radioactive calibration sources through bent guide tubes. The guide tubes are a few millimeters wide and extend up to 4 meters in overall length. The strings are Kevlar or Vectran thread just 0.35mm (0.014") in diameter, on which 1.8mm diameter copper tubes have been crimped after insertion of small activated iron wires. Teflon heat shrink is applied over the copper to improve sliding of the sources in the guide tubes to limit heat generation in the lower temperature portions of the cryostat.

Each string is attached to its own drive assembly. Each drive is equipped with a small stepper motor, encoder, load cell, and stop arm. The design houses three drives in one chamber. Bart Dana, Bill Koenig, and Ron Smith recently prototyped the drive assembly parts in the instrument shop and the parts were shipped to the Physics Department for assembly and testing. Eventually there will be 15 drives, enough for the full complement of 12 on CUORE and an additional spare chamber. Work continues on detailing chamber parts, design of guide tube mounts, and providing information for integration with the cryostat being designed in Italy.

It has been a challenge to pack a lot of functionality into a very compact vacuum chamber to fit within available space among other instruments atop the cryostat.

For more information on CUORE see http://crio.mib.infn.it/wig/Cuorepage/CUORE.php


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