Disentangling volumetric power and momentum losses in the JET-ILW scrape-off layer*

A large variation in the measured volumetric power, (1-f_cooling), and momentum, (1-f_mom), loss factors has been observed in theJET-ILW scrape-off layer (SOL), leveraging spectroscopic target electron temperature measurements and JET’s unique capability for separating the main-ion-driven net dissipation effects from impurity radiation. SOLPS-ITER and EDGE2D-EIRENE fluid-neutral edge plasma simulations have been carried out to decompose the dominant momentum and power loss channels in unseeded, high recycling  and low recycling nitrogen seeded seeded L-mode scenarios. The simulations show that while momentum losses in the unseeded cases are dominated by atom-molecule-plasma interactions, a similar momentum loss trend is obtained for the low recycling nitrogen seeding scan, consistent with experiment, due to a combination of poloidal viscosity, radial transport and atom-plasma interactions, even in the absence of significant molecular densities at the target. The steeper power loss trend in the low recycling nitrogen seeding scan results in a factor of three reduction in the (1-f_cooling)/(1-f_mom) ratio, demonstrating for the first time the variation in this important parameter in the context of two point model separatrix density scaling and SOL-pedestal integration.