Cea Saclay, in collaboration with the French SMI Sigmaphi, have fabricated a 50 kg solenoid with 2 km of Columbus MgB2 rectangular wire (3*0.7 mm²). The magnet was powered with 100 A at about 10 K and reached 4.2 T on the wire, with an external magnetic field of 3 T. A comparison between the protection and stability theoretical study and experimental results is presented. The quench propagation measurements have been performed at various temperatures, coil currents, and external fields. More than 20 quenches have been triggered using quench heaters mainly around the nominal design condition (10 K; 4 T and 50 A/mm² of overall conductor current). These measurements values are compared to the results of the design calculations. The differences with the numerical model are analyzed and a possible explanation of these differences is given by not taking into account eddy currents and ground insulation thickness. The validation of the experimental parameters is necessary for designing the protection of high field MgB2 magnets magnet in the frame of our development program. The performances of recent MgB2 wires allows us to reach magnetic fields over 5 T.