Physical Requirements and Implementation of SETC for Heat Flux Measurement in the Shape and Volume Rise Divertor of DIII-D

The upper divertor in the DIII-D facility has been optimized into a modular configuration to facilitate geometric modifications. The first phase involves implementing the Shape and Volume Rise (SVR) divertor to increase plasma volume and edge pressure, requiring careful consideration of heat flux measurements. By positioning the X-point in close proximity to the divertor targets, the SVR configuration maximizes plasma volume but imposes significant constraints on the power dissipation area, leading to radiation peaks near the divertor target. Meanwhile, it also broadens the flux expansion due to the shortened leg length. Therefore, heat flux measurements in the SVR divertor must encompass not only the region near the separatrix but also the broader divertor surface, accounting for the heat flux carried by various components. To achieve this, six specialized tiles were designed and installed in the upper divertor to mount Surface Eroding Thermocouples (SETCs). A poloidal array of 27 SETCs ensures heat flux measurement coverage across the entire modular divertor. Furthermore, a recessed SETC paired with a standard flush SETC was installed to provide comprehensive heat flux measurements, allowing for the differentiation between charged and non-charged particle contributions.