Speaker
Mr
Vsevolod Soukhanovskii
(USA)
Description
Recent NSTX results demonstrate that the snowflake divertor (SFD) configuration may provide a promising solution for mitigating steady-state and transient divertor heat loads and target plate erosion, and project favorably to future fusion devices. In NSTX, a medium-size spherical tokamak with high divertor heat flux (q_peak ≤ 15 MW/m^2, q_|| ≤ 200 MW/m^2), steady-state SFD configurations lasting up to 0.6 s (≤10 tau_E) in 4 MW NBI-heated H-mode discharges. In agreement with theory, the SFD geometry increased the plasma-wetted area, the X-point connection length, and the divertor volume. The SFD formation led to a stable partial detachment of the outer strike point otherwise inaccessible in the standard divertor at P_SOL=3 MW in NSTX. Peak divertor heat flux was reduced from 3-7 MW/m^2 to 0.5-1 MW/m^2, while radiated power and recombination rate increased. Additional seeding of deuterated methane increased divertor radiation further. Heat fluxes from Type I ELMs (Delta_W/W=7-10 %) were also significantly dissipated: peak target temperatures measured at peak ELM times reached 1000-1200 deg. C in the standard divertor phase and only 300-500 deg. C in the SFD phase. H-mode core confinement was maintained albeit the radiative detachment, while core carbon concentration was reduced by up to 50 %. To project SFD properties to future devices, a two-dimensional multi-fluid edge transport model based on the UEDGE code is developed, and initial simulations indicate large reductions in T_e , T_i, particle and heat fluxes due to the SFD geometry effects. In the planned NSTX Upgrade, two up-down symmetric sets of four divertor coils will be used to test the SFD for handling the projected steady-state 20-30 MW/m^2 peak divertor heat fluxes in 2 MA discharges up to 5 s long with up to 12 MW NBI heating. Supported by the U.S. DOE under Contracts DE-AC52-07NA27344, DE-AC02-09CH11466, DE-AC05-00OR22725, and DEFG02-99ER54519.
Country or International Organization of Primary Author
USA
Primary author
Mr
Vsevolod Soukhanovskii
(USA)
Co-authors
Dr
A. G. McLean
(LLNL)
Dr
A. L. Roquemore
(PPPL)
Dr
Ahmed Diallo
(PPPL)
Dr
B. P. Leblanc
(PPPL)
Dr
D. Battaglia
(PPPL)
Dr
D. D. Ryutov
(LLNL)
Dr
D. Mueller
(PPPL)
Dr
E. Kolemen
(PPPL)
Dr
E. Meier
(LLNL)
Mr
F. Scotti
(PPPL)
Dr
J. E. Menard
(PPPL)
Dr
M. Podesta
(PPPL)
Dr
M. V. Umansky
(LLNL)
Dr
R. E. Bell
(PPPL)
Dr
R. Kaita
(PPPL)
Dr
R. Maingi
(ORNL)
Dr
R. Raman
(U. Washington)
Dr
S. F. Paul
(PPPL)
Dr
S. Kaye
(PPPL)
Dr
S. P. Gerhardt
(PPPL)
Dr
T. D. Rognlien
(LLNL)
