Abstract
Alcator C-MOD has compared plasma performance with plasma facing components (PFCs) coated with boron to all-metal PFCs to assess projections of energy confinement from current experiments to next generation burning tokamak plasmas. Low-Z coatings reduce metallic impurity influx and diminish radiative losses leading to higher H mode pedestal pressure that improves global energy confinement through profile stiffness. RF sheath rectification along flux tubes that intersect the RF antenna is found to be a major cause of localized boron erosion and impurity generation. Initial lower-hybrid current drive (LHCD ) experiments (P{sub LH} < 900 kW) have demonstrated fully noninductive current drive at I{sub p} = 1.0 MA with good efficiency, I{sub drive} 0.4P{sub LH}/neoR (MA,MW, 10{sup 20}/m{sup -3},m). Understanding the mechanisms responsible for regulating the H-mode pedestal height is also crucial for projecting performance in ITER. Modeling of H-mode edge fueling indicates high self-screening to neutrals in the pedestal and scrape off layer (SOL), and reproduces experimental density pedestal response to changes in neutral source, including a weak variation of pedestal height and constant width. Similar to the scaling of edge pressure gradients in the H-mode pedestal observed previously, pressure gradients in the near SOL of Ohmic L-mode plasmas are observed
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Scott, S;
[1]
Bader, A;
[2]
Bakhtiari, M
[3]
- Princeton Plasma Physics Laboratory, Princeton (United States)
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA (United States)
- University of Wisconsin, Madison, WI (United States)
Citation Formats
Scott, S, Bader, A, and Bakhtiari, M.
Overview of Alcator C-Mod research program.
IAEA: N. p.,
2007.
Web.
Scott, S, Bader, A, & Bakhtiari, M.
Overview of Alcator C-Mod research program.
IAEA.
Scott, S, Bader, A, and Bakhtiari, M.
2007.
"Overview of Alcator C-Mod research program."
IAEA.
@misc{etde_20877643,
title = {Overview of Alcator C-Mod research program}
author = {Scott, S, Bader, A, and Bakhtiari, M}
abstractNote = {Alcator C-MOD has compared plasma performance with plasma facing components (PFCs) coated with boron to all-metal PFCs to assess projections of energy confinement from current experiments to next generation burning tokamak plasmas. Low-Z coatings reduce metallic impurity influx and diminish radiative losses leading to higher H mode pedestal pressure that improves global energy confinement through profile stiffness. RF sheath rectification along flux tubes that intersect the RF antenna is found to be a major cause of localized boron erosion and impurity generation. Initial lower-hybrid current drive (LHCD ) experiments (P{sub LH} < 900 kW) have demonstrated fully noninductive current drive at I{sub p} = 1.0 MA with good efficiency, I{sub drive} 0.4P{sub LH}/neoR (MA,MW, 10{sup 20}/m{sup -3},m). Understanding the mechanisms responsible for regulating the H-mode pedestal height is also crucial for projecting performance in ITER. Modeling of H-mode edge fueling indicates high self-screening to neutrals in the pedestal and scrape off layer (SOL), and reproduces experimental density pedestal response to changes in neutral source, including a weak variation of pedestal height and constant width. Similar to the scaling of edge pressure gradients in the H-mode pedestal observed previously, pressure gradients in the near SOL of Ohmic L-mode plasmas are observed to scale as I{sub p}{sup 2} squared and furthermore show a significant dependence on X-point topology. Fast camera images of intermittent turbulent structures at the plasma edge show they travel coherently through the SOL with a broad radial velocity distribution having a peak at about 1% of the ion sound speed, in qualitative agreement with theoretical models. Fast D{sub a} diagnostics during gas puff imaging show a complex behavior of discrete ELMs, starting with an N{sub toroidal} = 10 precursor oscillation followed by a rapid primary ejection as the pedestal crashes and then multiple, slower secondary ejections. The potential to mitigate disruptions in ITER through massive gas-jet impurity puffing has been extended to higher plasma pressures and shorter disruption times. The fraction of total plasma energy radiated increases with the Z of the impurity gas, reaching 90% for krypton. A Phase Contrast Imaging diagnostic has been used to study the structure of Alfven cascades and turbulent density fluctuations in plasmas with an internal transport bar. (author)}
place = {IAEA}
year = {2007}
month = {Mar}
}
title = {Overview of Alcator C-Mod research program}
author = {Scott, S, Bader, A, and Bakhtiari, M}
abstractNote = {Alcator C-MOD has compared plasma performance with plasma facing components (PFCs) coated with boron to all-metal PFCs to assess projections of energy confinement from current experiments to next generation burning tokamak plasmas. Low-Z coatings reduce metallic impurity influx and diminish radiative losses leading to higher H mode pedestal pressure that improves global energy confinement through profile stiffness. RF sheath rectification along flux tubes that intersect the RF antenna is found to be a major cause of localized boron erosion and impurity generation. Initial lower-hybrid current drive (LHCD ) experiments (P{sub LH} < 900 kW) have demonstrated fully noninductive current drive at I{sub p} = 1.0 MA with good efficiency, I{sub drive} 0.4P{sub LH}/neoR (MA,MW, 10{sup 20}/m{sup -3},m). Understanding the mechanisms responsible for regulating the H-mode pedestal height is also crucial for projecting performance in ITER. Modeling of H-mode edge fueling indicates high self-screening to neutrals in the pedestal and scrape off layer (SOL), and reproduces experimental density pedestal response to changes in neutral source, including a weak variation of pedestal height and constant width. Similar to the scaling of edge pressure gradients in the H-mode pedestal observed previously, pressure gradients in the near SOL of Ohmic L-mode plasmas are observed to scale as I{sub p}{sup 2} squared and furthermore show a significant dependence on X-point topology. Fast camera images of intermittent turbulent structures at the plasma edge show they travel coherently through the SOL with a broad radial velocity distribution having a peak at about 1% of the ion sound speed, in qualitative agreement with theoretical models. Fast D{sub a} diagnostics during gas puff imaging show a complex behavior of discrete ELMs, starting with an N{sub toroidal} = 10 precursor oscillation followed by a rapid primary ejection as the pedestal crashes and then multiple, slower secondary ejections. The potential to mitigate disruptions in ITER through massive gas-jet impurity puffing has been extended to higher plasma pressures and shorter disruption times. The fraction of total plasma energy radiated increases with the Z of the impurity gas, reaching 90% for krypton. A Phase Contrast Imaging diagnostic has been used to study the structure of Alfven cascades and turbulent density fluctuations in plasmas with an internal transport bar. (author)}
place = {IAEA}
year = {2007}
month = {Mar}
}