Author: John E. RicePublisher:
ISBN:
Category :
Languages : en
Pages : 13
Book Description
Observations of Alcator C-Mod Plasmas from a 5 Chord High Energy Resolution X-ray Spectrometer Array
X-ray Observations of Up-down Impurity Density Asymmetries in Alcator C-Mod Plasmas
Author: John E. RiceChemical Abstracts
Author: X-ray Observations of Central Toroidal Rotation in Ohmic Alcator C-Mod Plasmas
Author: John E. RiceFusion Nucléaire
Author: X-ray and VUV Observations of Mo23-Mo33 Brightness Profiles from Alcator C-Mod Plasmas
Author: John E. RiceObservations of Cold, High Density Plasma in the Private Flux Region of the Alcator C-Mod Divertor
Author: Christopher James BoswellPublisher:
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.
Lower Hybrid Current Drive on Alcator C-Mod
Author: Robert Thomas MumgaardPublisher:
ISBN:
Category :
Languages : en
Pages : 349
Book Description
Lower Hybrid Current Drive (LHCD) is a promising technique to sustain tokamak plasmas and provide control over the current profile--two important capabilities required for the development of tokamak fusion reactors. Upgraded measurement capabilities on the Alcator C-Mod Tokamak create a unique opportunity to study the plasma's toroidal electric current profile at magnetic fields, plasma densities, and magnetic geometries anticipated in future reactors in stationary discharges dominated by lhcd. The Motional Stark Effect (MSE) diagnostic uses polarized light to infer the plasma's internal current profile. The MSE diagnostic deployed on the Alcator C-Mod Tokamak previously experienced unacceptable calibration drift and sensitivity to partially-polarized background light that limited its ability to measure magnetic field pitch-angles. A comprehensive analytic study of the origin of polarization angle errors in MSE diagnostics and an experimental study using a robotic calibration system were conducted. Insight from this study guided the fabrication and installation of a first-of-a-kind in-situ calibration system for MSE diagnostics--a long sought capability-- and the development of thermal isolation schemes for the periscope. An experimental study of the effect of partially polarized background light identified this as a significant source of systematic error. Partial-polarization upon reflection was identified as the mechanism that leads to polarized light in a tokamak. Visible bremsstrahlung, divertor emission, and blackbody emission were identified as the dominant sources of light. A new technique, MSE multi-spectral line polarization (MSE-MSLP), was developed to measure the polarization on a single sight line in multiple wavelengths simultaneously using a high-throughput polarization polychromator. Wavelength-interpolation of the background light polarization utilizing this hardware decreases the error from background subtraction by a factor of 5-10 relative to time-interpolation, drastically improving the measurement quality while eliminating the need for neutral beam pulsing. The method also allows for simultaneous measurement of multiple polarized transitions within the Stark multiplet. The upgraded MSE diagnostic was used to measure the magnetic field pitch angle profile in plasmas with some or all of the plasma current driven by lhcd. Measurements were made across a range of single-parameter scans: lhcd power, loop voltage, plasma density, plasma current, and launched n// spectrum. The current profile is observed to broaden during lhcd, but consistently has significant on-axis current density, even in fully non-inductive plasmas. The current profile and hard x-ray (HXR) profiles are observed to be most sensitive to plasma current, with higher current yielding broader profiles. The current and HXR profiles as well as global current-drive efficiency are insensitive to changes in n// or loop voltage. Numerical simulations by the ray-tracing Fokker-Planck GENRAY/CQL3D code reproduce the total measured current in non-inductive conditions but fail to accurately predict the current and HXR profiles; the simulations consistently predict more current drive in the outer half of the plasma than is observed. This leads to a flattening of the HXR profile compared to the experimental profiles. These qualitative discrepancies persist across the range of plasma parameters scanned. Varying code inputs within their measurement uncertainties and adding experimentally-constrained levels of fast-electron diffusion do not reconcile profile discrepancies. Some qualitative profile trends in single parameter scans are reproduced by the simulations including broadening of profiles at higher current, and a weak dependence on the launched n//spectrum. However, HXR profile self-similarity across different densities and powers is not reproduced. These new comparisons between profile measurements and simulation suggest that the simulations are missing important physics in this operational regime.
Observations of Central Toroidal Rotation in ICRF Heated Alcator C-Mod Plasmas
Author: John E. RiceExperimental and Gyrokinetic Studies of Impurity Transport in the Core of Alcator C-Mod Plasmas
Author: Nathaniel Thomas HowardPublisher:
ISBN:
Category :
Languages : en
Pages : 238
Book Description
Using a unique set of diagnostics and modeling tools, a comprehensive study of impurity transport was performed on Alcator C-Mod L-mode discharges. A new, multi-pulse laser blow-off system was designed and constructed to introduce trace amounts of non-recycling, non-intrinsic, impurities in the plasma edge. This system was coupled with an x-ray crystal spectrometer, a single chord x-ray/ultraviolet spectrometer, and measurement of the laser blow-off neutral source at the plasma edge to provide full, time-evolving, radial profiles of a single impurity charge state. An iterative X2 minimization scheme was created to infer the experimental impurity transport coefficients and their uncertainty by minimizing the difference in the measured and STRAHL simulated emission. These measurements and data analysis methodology allowed for determination of impurity transport coefficient profiles with realistic errors from 0.0