Access to pedestal pressure relevant to burning plasmas on the high magnetic field tokamak Alcator C-Mod

Dataset · Wed Oct 03 00:00:00 EDT 2018

DOI:https://doi.org/10.7910/DVN/0JOUCX· OSTI ID:1878746

Hughes, J. W.; Snyder, P. B.; Reinke, M. L.; LaBombard, B.; Mordijck, S.; Scott, S.; Tolman, E.; Baek, S. G.; Golfinopoulos, T.; Granetz, R. S.; Greenwald, M.; Hubbard, A. E.; Marmar, E.; Rice, J. E.; White, A. E.; Whyte, D. G.; Wilks, T.; Wolfe, S.

Experiments on the Alcator C-Mod tokamak have utilized reactor-relevant magnetic fields to sustain substantially higher pedestal pressure than in other devices and allow close approach to the ITER H-mode baseline target pedestal pressure of 90 kPa. The EPED model, which couples the physics of transport driven by kinetic ballooning modes and MHD instabilities arising from peeling-ballooning modes, predicts the pressure profile at the onset of edge-localized modes (ELMs), and yields to lowest order a critical-βN like behavior for the pedestal: p∝Bt×Bp ( ∝Bt^2 for fixed edge q). C-Mod routinely accesses edge plasma pressure in excess of 30 kPa, often by using a high-density (ne>3×10^20 m^-3) approach to high confinement, taking advantage of a regime known as enhanced D-alpha (EDA) H-mode. In the EDA H-mode, plasma transport regulates both the pedestal profiles and the core impurity content, thus holding the pedestal stationary at just below the peeling-ballooning stability boundary. This stationary ELM-suppressed regime has approached the maximum pedestal predicted by EPED at these densities: 60 kPa. This in turn gives rise to volume-averaged core plasma pressure in excess of 0.2MPa, a world record value for a magnetic fusion device. Another approach to achieving high pressure utilizes a pedestal limited by current-driven modes at low collisionality, in which pressure increases with density and which allows access to a higher EPED solution, termed “super-H”. C-Mod experiments at reduced density (ne<2×10^20 m^-3) and strong plasma shaping (δ>0.5) accessed this regime, producing pedestals with pressures up to 80kPa (approximately 90% of the ITER target) and temperatures of nearly 2 keV. In a number of these hot H-modes, we observe strong edge instabilities at low toroidal mode number (n=1) when pedestal pressure approaches predicted values from EPED, showing that current-driven MHD modes can serve as a limit on the pedestal in a metal-walled tokamak at high pressure and low collisionality.

• Research Organization: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center; General Atomics, San Diego, CA (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); College of William and Mary, Williamsburg, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• DOE Contract Number: FC02-99ER54512; FG02-95ER54309; FC02-06ER54873; AC02-09CH11466; AC05-00OR22725; SC0007880
• OSTI ID: 1878746
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY