An irrigated ablation catheter includes a tip electrode with a thin shell and a plug, defining a plenum chamber. The tip electrode has an inlet of a predetermined size and noncircular shape, and a predetermined number of outlet fluid ports having a predetermined diameter in the shell wall. The tip electrode thus considers a diffusion ratio of total fluid output area to fluid input area, and a fluid port ratio, and considers a fluid inlet aspect ratio where the fluid inlet has a noncircular radial cross-section. The plenum chamber has a narrow proximal portion opening to a wider distal portion so that fluid pressure decreases while fluid velocity increases thereby increasing turbulence which decreases momentum for a more uniform distribution of fluid in the tip electrode. Extending distally from the plug is a baffle member shaped to diffuse fluid entering the tip electrode and to house an electromagnetic position sensor.
