Research teams think that there is little damage, if any, to the two large particle-physics experiments in the Soudan mine in Minnesota, following a fire in the access shaft on 17 March, which shut down both the mine and the experiments located 800 m underground.
When the fire was detected at around 9 p.m., the fire-protection system shut down the power to the Soudan Underground Laboratory, as designed. No personnel were in the mine at the time. The cause of the fire is believed to be linked to shaft-maintenance work earlier in the day.
Fire fighters extinguished the fire by pumping some 265,000 litres of water and fire-extinguishing foam down the access shaft. Some of the foam entered the caverns of the underground laboratory, which is managed by the University of Minnesota. The laboratory houses the 5000-tonne far detector of the Main Injector Neutrino Oscillation Search (MINOS) experiment, the Cryogenic Dark Matter Search (CDMS) experiment, managed by Fermilab, and several other smaller experiments.
Ten days after the fire, the first crew of scientists returned to the laboratory as electricians began restoring power. Residue of fire-fighting foam was found across large parts of the laboratory, however, researchers from CDMS found no apparent damage to their experiment. During the 10-day power outage, the experiment, which operates ultra-sensitive particle detectors at a temperature of about 50 mk, warmed to room temperature without losing vacuum. When the team turned the power back on, all cryogenic systems functioned as normal.
No water or foam was found on the electronics for MINOS. The experiment’s large electromagnetic coil was partially immersed in water and will be carefully dried out before being used once more. The coil provides the neutrino detector with a magnetic field for charged-particle identification.
There are several smaller experiments in the mine, including the CoGeNT dark-matter search. An assessment of these experiments will be made when full access to the underground laboratory is available.
Complete clean-up, final assessment and restart of the experiments will occur once a new power cable has been installed in the shaft, allowing full power to be restored to the laboratory.
