This paper describes results from the initial thermal barrier experiments in the Tandem Mirror Experiment-Upgrade (TMX-U). Strong end plugging has been produced using a combination of ECRH gyrotrons with sloshing ion beam injection. Plugging has been achieved with a central cell higher than that of the end plugs. In these low-density central cell experiments (7 x 10/sup 11/ cm/sup -3/) the axial losses (tau/sub parallel to/ = 20 to 80 ms) are smaller than the radial losses (tau/sub perpendicular to/ = 4 to 8 ms). Although no direct measurements are yet available to determine if a thermal barrier potential dip is generated, these experiments support many theoretical features of the thermal barrier concept.