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The fragmentation process in massive star-forming regions is one of thecontemporary problems in astrophysics, and several physical processes have beenproposed to control the fragmentation including turbulence, magnetic field,rotation, stellar feedback, and gravity. However, the fragmentation process hasbeen poorly studied at small spatial scales well below 1000 AU. We aim to useALMA (Atacama Large Millimeter and Submillimeter Array) high angular resolutiondata to identify the fragments in W51 IRS2 and to study the fragmentationproperties on a spatial scale of 200 AU. We used ALMA data of W51 IRS2 fromthree projects, which give an angular resolution of 0.028$^{\prime\prime}$ (144AU) at millimeter wavelengths. We identified compact fragments by using {\ituv}-range constrained 1.3 mm continuum data. A Mean Surface Density ofCompanions (MSDC) analysis has been performed to study the separations betweenfragments. A total number of 33 continuum sources are identified and 29 out ofthem are defined as fragments in the surveyed region.The MSDC analysis revealstwo breaks corresponding to spatial sales of 1845 AU and 7346 AU, indicative ofa two-level clustering phenomenon, along with a linear regime below 1845 AU,mostly associated with W51 North, whose slope is consistent with the slope forthe clustering regime of other cluster-like regions in the Galaxy. The typicalmasses and separations of the fragments as well as the relation between densityand number of fragments can be explained through a thermal Jeans processoperating at high temperatures of 200--400 K, consistent with previousmeasurements of the temperature in the region, and produced by the nearbymassive stars. Therefore, although W51 IRS2 seems to be undergoing a thermallyinhibited fragmentation phase, this does not seem to prevent the formation of aprotocluster associated with W51 North.

W51North: A protocluster emerging out of a thermally inhibited fragmenting cloud