Observations of Cold, High Density Plasma in the Private Flux Region of the Alcator C-Mod Divertor PDF Download
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Author: Christopher James Boswell Publisher: ISBN: Category : Languages : en Pages : 10
Book Description
Significant plasma density has been observed in the private flux zone of the Alcator C-Mod tokamak. The behavior of the Dg emission profiles is consistent with the source of the plasma being due to an E x B drift generated by a poloidal temperature gradient. The plasma flux due to this drift is derived and evaluated. A plasma flux into the private flux zone is inferred by measurements of volumetric recombination using a tangentially viewing CCD camera and several spectroscopic views observing the high n-lines of the Do Balmer series. For the case of an attached divertor the inferred plasma flux to the PFZ has a linear scaling with respect to plasma pressure, as is expected from the temperature-gradient-induced, E x B drift.
Author: Christopher James Boswell Publisher: ISBN: Category : Languages : en Pages : 10
Book Description
Significant plasma density has been observed in the private flux zone of the Alcator C-Mod tokamak. The behavior of the Dg emission profiles is consistent with the source of the plasma being due to an E x B drift generated by a poloidal temperature gradient. The plasma flux due to this drift is derived and evaluated. A plasma flux into the private flux zone is inferred by measurements of volumetric recombination using a tangentially viewing CCD camera and several spectroscopic views observing the high n-lines of the Do Balmer series. For the case of an attached divertor the inferred plasma flux to the PFZ has a linear scaling with respect to plasma pressure, as is expected from the temperature-gradient-induced, E x B drift.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Calculations have been performed which demonstrate the possibility of operating poloidal divertors at high densities and low temperatures. This operating regime is caused primarily by ionization of recycling neutral gas near the divertor neutralizer plate which amplifies the input particle flux thereby raising the plasma density and lowering the plasma temperature. Low temperature, high density operation of poloidal divertors would ease the design requirements for future large tokamaks such as INTOR or FED by reducing the erosion rate in the divertor and reducing the neutral density and the associated charge exchange erosion near the main plasma. This regime may have already been observed on several divertor and limiter experiments.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
We study experiments in Alcator C-Mod to assess the level of toroidal asymmetry in divertor conditions resulting from poloidally and toroidally localized extrinsic impurity gas seeding show a weak toroidal peaking (~1.1) in divertor electron temperatures for high-power enhanced D-alpha H-modeplasmas. This is in contrast to similar experiments in Ohmically heated L-modeplasmas, which showed a clear toroidal modulation in the divertor electron temperature. Modeling of these experiments using the 3D edge transport code EMC3-EIRENE [Y. Feng et al., J. Nucl. Mater. 241, 930 (1997)] qualitatively reproduces these trends, and indicates that the different response in the simulations is due to the ionization location of the injected nitrogen. Low electron temperatures in the private flux region (PFR) in L-mode result in a PFR plasma that is nearly transparent to neutral nitrogen, while in H-mode the impurities are ionized in close proximity to the injection location, with this latter case yielding a largely axisymmetric radiation pattern in the scrape-off-layer. In conclusion, the consequences for the ITER gas injection system are discussed. Quantitative agreement with the experiment is lacking in some areas, suggesting potential areas for improving the physics model in EMC3-EIRENE.
Author: Publisher: ISBN: Category : Languages : en Pages : 4
Book Description
Recently, much effort has been dedicated to understanding the bifurcation involved in the transition from a low to high confinement regime. While several theories have been brought forward, many factors remain to be elucidated, one of which involves the role played by neutral particles in the evolution of a transport barrier near the edge of the plasma. Alcator C-Mod is especially well suited for the study of neutral particle effects, mainly because of its high plasma and neutral densities, and closed divertor geometry. Alcator C-Mod employs ICRF as auxiiiary heating for obtaining a high confinement regime, although ohmic H-modes are routinely obtained as well. The neutrals can enter the edge dynamics through the particle, momentum and energy balance. In the particle balance, the source of neutrals has to be evaluated vis-8-vis the formation of the edge density pedestal. It is widely believed that plasma rotation is an important factor in reducing transport. In this case, neutrals could act as a momentum sink, through the charge-exchange process. That same process can also modify the energy balance of the plasma near the edge by increasing the cross-field heat flux. These effects are quite difficult to measure experimentally, in large part because neutral particle diagnosis is not an easy task, and because of the inherent 3-dimensional aspect of the problem. Consequently, the neutral s spatial and energy distributions are usually not well known. In Alcator C-Mod, we recently implemented a series of diagnostics for the purpose of measuring these distributions. They include measurements of the neutral pressure at many locations around the tokamak, and spatially resolved measurements of Lyman-a and charge-exchange power emission. A high-resolution multichord (20 channels) tangential view of neutral deuterium emission (Lyman-a) has been recently installed near the midplane. The viewing area covers approximately 4 cm across the separatrix, with a nominal 2 mm radial resolution. Standard Abel inversion techniques give the local Lyman-a emission. In conjunction with electron density and temperature, we can infer the local ionization rate and neutral density profiles. Two types of bolometer arrays (16 channels each), one being sensitive and the other insensitive to power carried by neutrals, view the plasma cross-section, tangentially at the midplane of the tokamak. By Abel inverting the difference between the 2 measurements, we infer the local power emissivity carried by neutrals[11].
Author: Christopher James Boswell
Author: Christopher James Boswell
Author: John E. Rice
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Author: John E. Rice
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Author: A. Niemczewski
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Author: John Anthony Goetz