Breakdown of 3He-A superflow in low magnetic fields

Using a sensitive differential pressure gauge, we have measured the limits to dissipationless superflow in bulk superfluid 3He-A far from stabilizing walls. We report the first quantitative measurements of the breakdown of bulk superflow in the A phase. In addition to confirming the existence of a finite critical current in bulk uniform textures, we have discovered an unexpected tortuous texture in which there is an even larger critical current. These results indicate that the current theoretical models for determining textures are incomplete.