  $Nb_{3}Sn$ performance in RF fields is limited to fields far below its
superheating critical field. Poor thermal conductivity of $Nb_{3}Sn$ has been
speculated to be the reason behind this limit. In order to better understand
the contribution of $Nb_{3}Sn$ thermal conductivity to its RF performance, we
simulated numerically with Matlab program*(based on SRIMP and HEAT codes) the
limiting fields under different realistic conditions. Our simulations indicate
that limiting fields observed presently in the experiments with RF fields
cannot be explained by the thermal impedance of $Nb_{3}Sn$ alone. The results
change significantly in the presence of higher losses due to extrinsic
mechanisms.
