Lawrence Berkeley National Laboratory

The first magnets for the muon ionization cooling experiment will be the tracker solenoids that form the ends of the MICE cooling channel. The primary purpose of the tracker solenoids is to provide a uniform 4 T field (to better than +-0.3 percent over a volume that is 1 meter long and 0.3 meters in diameter) spectrometer magnet field for the scintillating fiber detectors that are used to analyze the muons in the channel before and after ionization cooling. A secondary purpose for the tracker magnet is the matching of the muon beam between the rest of the MICE cooling channel and the uniform field spectrometer magnet. The tracker solenoid is powered by three 300 amp power supplies. Additional tuning of the spectrometer is provided by a pair of 50 amp power supplies across the spectrometer magnet end coils. The tracker magnet will be cooled using a pair of 4 K pulse tube coolers that each provide 1.5 W of cooling at 4.2 K. Final design and construction of the tracker solenoids began during the summer of 2006. This report describes the progress made on the construction of the tracker solenoids.