Hydrogen and Helium Edge-Plasmas Comparison of high and low recycling T.D. Rognlien and M.E. Rensink Lawrence Livermore National Lab Presented at the ALPS/APEX Meeting Argonne National Lab May 8-12, 2
Outline 1. High- and low-recycling hydrogen plasmas 2. ARIES-RS results 3. Helium spatial concentrations
High and low recycling have similar plate heat flux profiles ITER-like geometry with 15 MW into SOL Heat flux to plate (MW/m**2) 8 4 R = 1 R is particle recycling coeff. R =.5 1-D plasma pressure balance is broken by radial transport for R=.5 case 4 8 12 Distance from separatrix at plate (cm) 2 Electron temperature (ev) 1 R =.5 n ~ 1/T e R = 1 4 8 12 Distance from separatrix at plate (cm)
Edge plasma changes from low to high recycling Ion parallel velocity (km/s) 8 4 Ion parallel velocity v for high recycling (R=1).1 x v for low recycling (R=.25) Electron temperature in SOL (ev) 4 2 Electron temperature Low recycling High recycling X-point 4 8 12 Poloidal distance (m) Top of machine Divertor plate
Low recycling yields hot edge plasma unless there is very large DT particle fueling Separatrix electron temperature (ev) 12 8 4 Low recycling, R=.25 T e 4 8 n i Core DT particle fueling current (ka) 4 2 19 3 Separatrix density (1 1/m )
Mesh obtained for standard ARIES-RS with symmetric double-null divertor 8 Symmetry plane 7 6 5 4 Inner divertor Outer divertor 4 5 6 7
Small modification to poloidal B-field coils used to produce single-null configuration 4 Resulting divertor plasma parameters given in a memo -4 3 5 7
Low recycling hydrogen can give much better helium compression in divertor 21 1 Ion density (m -3 ) 1 2 1 19 1 18 1 17 R =.99 DT R =.99 He Helium D-T High DT recycling 16 1 1 2 D-T Ion density (m -3 ) 1 19 1 18 R =.5 DT R =.99 He Low DT recycling Helium 1 17 X-point 5 1 15 Poloidal distance from top (m) Orthogonal plate
Helium flux displaced toward outer wall for vertical divertor plate 1% helium at the core-edge boundary R_hydrogen =.5, R_helium =.95 Orthogonal divertor plate Vertical divertor plate Particle flux normal to plate (1/s m**2) Separatrix D-T D-T + Particle flux normal to plate(1/s m**2) Separatrix D-T + D-T Particle flux normal to plate (1/s m**2) He ++ Helium He + Particle flux normal to plate(1/s m**2) Helium He + He ++ Distance along divertor plate (m) Distance along divertor plate (m)
Helium ion density concentrates near wall for vertical divertor plate 17-3 R =.5, R =.99, n at core boundary = 4 x 1 m DT He He Vertical position (m) 4 3 Orthogonal divertor plate Helium density 1 17 1 18 1 19 2 vertical position (m) 4 3 Helium density 1 16 1 17 1 18 2 Vertical divertor plate 7 8 9 Major radius (m)
Helium gas density also concentrates near wall for vertical plate 2.6 Vertical position (m) 2.4 2.2 He gas density 1 17 1 18 1 19 Orthogonal plate 8. 8.2 8.4 3. Vertical position (m) 2.6 2.2 He gas density 1 17 1 18 1 19 Vertical plate 7.4 7.8 8.2 Major radius (m)
Summary 1. High- and low-recycling hydrogen plasmas - poloidal flow toward divertor much reduced for high recycling plamas - major impact on impurities - edge density for low recycling is controlled by fueling; more analysis of cases with low edge density needed 2. ARIES-RS results - an MHD equilibrium for single null now available - divertor plasma weakly attached assuming 9% of core power radiated; strongly attached otherwise 3. Helium spatial concentrations - low recycling with large fueling causes large helium densities near the plate - enhances duct pumping - tilted divertor plate forces helium toward outer wall