Particle control via cryopumping and its impact on the edge plasma profiles of Alcator C-Mod
[1];
[2];
[1];
[3];
[4]
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
- College of William and Mary, Williamsburg, VA (United States)
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
At the high ne proposed for high-field fusion reactors, it is uncertain whether ionization, as opposed to plasma transport, will be most influential in determining ne at the pedestal and separatrix. A database of Alcator C-Mod discharges is analyzed to evaluate the impact of source modification via cryopumping. The database contains similarly-shaped H-modes at fixed IP = 0.8 MA and Bt = 5.4 T, spanning a large range in Pnet and ionization. Measurements from an edge Thomson scattering system are combined with those from a midplane-viewing Lyα camera to evaluate changes to ne and Te in response to changes in ionization rates, Sion ∙ $$n^{sep}_e$$ and $$T^{ped}_e$$ are found to be most sensitive to changes to $$S^{sep}_{ion}$$, as opposed to $$n^{ped}_e$$ and $$T^{sep}_e$$. Dimensionless quantities, namely αMHD and v*, are found to regulate attainable pedestal values. Select discharges at different values of Pnet and in different pumping configurations are analyzed further using SOLPS-ITER. It is determined that changes to plasma transport coefficients are required to self-consistently model both plasma and neutral edge dynamics. Pumping is found to modify the poloidal distribution of atomic neutral density, n0, along the separatrix, increasing n0 at the active X-point. Opaqueness to neutrals from high ne in the divertor is found to play a role in mediating neutral penetration lengths and hence, the poloidal distribution of neutrals along the separatrix. Pumped discharges thus require a larger particle diffusion coefficient than that inferred purely from 1D experimental profiles at the outer midplane.
- Research Organization:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Fusion Energy Sciences (FES)
- Grant/Contract Number:
- AC05-00OR22725; SC0007880; SC0014264; SC0021629
- OSTI ID:
- 2483922
- Journal Information:
- Nuclear Materials and Energy, Journal Name: Nuclear Materials and Energy Vol. 42; ISSN 2352-1791
- Publisher:
- ElsevierCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Similar Records
Separating divertor closure effects on divertor detachment and pedestal shape in DIII-D
Comparison of Plasma Parameters Between QH and ELMing Phases of the Same Discharges