Dependence of the Heat Flux Width on the Connection Length in DIII-D

The heat flux width characterizes the scale length of peak power deposition in the divertor. The total heat flux width, $\lambda_{int}\approx \lambda_q+1.74S$, has contributions from the scrape-off layer itself, characterized by the quantity $\lambda_q$, and from the private flux region, characterized by a Gaussian-like width, $S$. Most work to date has focused on the physics of $\lambda_q$, with the essential finding that it depends approximately inversely on the plasma current. Here, the emphasis is on the $S$ parameter and, in particular, its dependence on the connection length, $L_{conn}$. Data from high X-point discharges ($L_{conn}\sim\,$30 m) have been used to extend the DIII-D heat flux width database beyond discharges with a standard divertor configuration ($L_{conn}\sim\,$20 m). Snowflake divertor discharges ($L_{conn}>40\,$m) will also be analyzed to further extend the range of $L_{conn}$. Preliminary results indicate that $S$ increases with Lconn, consistent with $S$ being determined by a diffusive process. This result has important implications for advanced divertor designs as it demonstrates that long connection lengths increase the heat flux width.