Passive Detection of High Energy Particle Loss using Rippled Tiles*

A novel detection approach for energetic particle loss is being implemented on DIII-D. Lost energetic ions from neutral beam injections can produce a measurable temperature change on the DIII-D outer wall. The lost ion heat profiles are however challenging to distinguish from that of the scrape-off layer heat flux. The new detection technique relies on modified tile geometries composed of short barriers that prevent small gyroradius particles from impacting the downstream wall surface and consequently create unique heat patterns on the modified tile surface. The barrier geometry sets the energetic particle energy and pitch angle sensitivity, and both are modeled to inform the tile design. Three rippled tiles are in use on DIII-D. Temperature measurements from a wide-angle, high-speed infrared camera indicate that the rippled tile shapes can affect downstream ion impacts. This passive detection technique is potentially applicable to ITER-class fusion devices.