Download or read book Limiter Hard X ray Emission Studies During Lower Hybrid Current Drive Experiments on the Alcator C Tokamak written by Daniel S. Pappas and published by . This book was released on 1984 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Lower Hybrid Current Drive on Alcator C Mod written by Robert Thomas Mumgaard and published by . This book was released on 2015 with total page 349 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Quantification of Lower Hybrid Wave Absorption in the Edge of the Alcator C Mod Tokamak written by Ian Charles Faust and published by . This book was released on 2016 with total page 209 pages. Available in PDF, EPUB and Kindle. Book excerpt: A 1 MW Lower Hybrid Current drive (LHCD) radiofrequency system is used to replace inductive drive on the Alcator C-Mod tokamak. It was designed to test Advanced Tokamak (AT) scenarios for future steady-state diverted, high field tokamaks. However, at reactor-relevant densities (n̄e > 1 . 10 20 m-3), an anomalous current drive loss is observed. This loss, known as the LHCD density limit, occurs in diverted plasmas and is correlated with the plasma current and plasma density. Several mechanisms have been implicated in the loss of current drive, with both experimental and theoretical results suggesting edge power loss. Power modulation is a standard technique used for characterizing power sources and plasma power balance. In this case, the Lower Hybrid radiofrequency (LHRF) power is modulated in time in a set of plasmas across the density range from efficient to negligible current drive. This data is used to characterize the absorption of LHRF power through the calculation of the LHRF power balance within 15%, typical of power balance studies. This power balance is used to derive characteristics of the cause behind the LHCD density limit. The immediate nature of LHRF-induced conducted and radiated power losses confirm that LHRF power is absorbed in the edge plasma, even at the lowest densities. The edge losses increase to balance the reduced current drive, indicating that the observed power in the scrape-off-layer (SOL) limits the available power for current drive and the edge losses represent a parasitic mechanism. Unlike edge losses of other radiofrequency systems, this absorption occurs with a high degree of toroidal symmetry near the plasma separatrix. This indicates absorption occurs just inside the separatrix, or just outside the separatrix over multiple SOL traversals. Measurements of the poloidal distribution of ionization and recombination in the edge were made using a specially designed Ly[alpha] pinhole camera. It utilizes a MgF2 filter and AXUV diode array to measure Ly[alpha] emission from the lower to upper divertor. Edge deposited LHRF power was found to promptly ionize the active divertor plasma in all diverted topologies. This result highlights the power flow and importance of the divertor plasma in the LHCD density limit. Three independent characteristics indicate the thermal absorption of LHRF power. First, in- /out balance of radiated and conducted LHRF power change with the reversal of the tokamak magnetic fields. Second, comparisons of the conducted heat via Langmuir probes and IR thermography are similar with and without LHRF power. Lastly, the Langmuir probe ratio of Vf l/Te does not significantly modulate with modulated LHRF. A second experiment utilized a high strike-point diverted discharge to determine the edge loss of fast electrons. The high strike point could be observed using the hard X-ray camera, which can compare core and edge X-ray emission. The measured count rates from thick-target bremsstrahlung were interpreted into fast electron fluxes using the Win X-ray code. Theoretical treatments of the fast-electron confinement time were also calculated for Alcator C-Mod. In all cases the fast-electron edge losses are minimal and will be unimportant for future tokamaks due to the small fast electron diffusivity and their large size. The loss of current drive in high density diverted plasmas correlates with high edge plasma collisionality. The newly derived characteristics set stringent requirements in nk for electron Landau damping to cause the edge absorption of LHRF power. Several observed attributes, namely high frequency modulation and low density absorption do not correlate with Landau damping characteristics. However, parasitic collisional absorption in the divertor plasma yields the necessary plasma current, topology, symmetry, thermal, and ionization characteristics. High divertor plasma collisionality is expected if not required for future tokamaks. LHRF systems of future tokamaks must must avoid propagation through collisional regions, even on the first traversal through the SOL.
Download or read book High Energy X ray Measurements During Lower Hybrid Current Drive on the Alcator C Tokamak written by Scott Charles Texter and published by . This book was released on 1986 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Lower Hybrid Heating and Current Drive on the Alcator C Mod Tokamak written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: On the Alcator C-Mod tokamak, lower hybrid current drive (LHCD) is being used to modify the current profile with the aim of obtaining advanced tokamak (AT) performance in plasmas with parameters similar to those that would be required on ITER. To date, power levels in excess of 1 MW at a frequency of 4.6 GHz have been coupled into a variety of plasmas. Experiments have established that LHCD on C-Mod behaves globally as predicted by theory. Bulk current drive efficiencies, n20IlhR/Plh ~ 0.25, inferred from magnetics and MSE are in line with theory. Quantitative comparisons between local measurements, MSE, ECE and hard x-ray bremsstrahlung, and theory/simulation using the GENRAY, TORIC-LH CQL3D and TSC-LSC codes have been performed. These comparisons have demonstrated the off-axis localization of the current drive, its magnitude and location dependence on the launched n.
Download or read book Lower Hybrid Current Drive Experiments on the Alcator C and the Versator II Tokamaks written by Alcator C Group and published by . This book was released on 1983 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Lower Hybrid Current Drive Experiments on the MIT Alcator C and Versator II Tokamaks written by Alcator C Group and published by . This book was released on 1985 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Lower Hybrid Current Drive Experiments in Alcator C Mod written by and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A Lower Hybrid Current Drive (LHCD) system has been installed on the Alcator C-MOD tokamak at MIT. Twelve klystrons at 4.6 GHz feed a 4x22 waveguide array. This system was designed for maximum flexibility in the launched parallel wave-number spectrum. This flexibility allows tailoring of the lower hybrid deposition under a variety of plasma conditions. Power levels up to 900 kW have been injected into the tokomak. The parallel wave number has been varied over a wide range, n.
Download or read book Energy Research Abstracts written by and published by . This book was released on 1987 with total page 644 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book RLE Progress Report written by Massachusetts Institute of Technology. Research Laboratory of Electronics and published by . This book was released on 1984 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Lower Hybrid Heating Current Drive Experiments on the Alcator C and Versator II Tokamaks written by Miklos Porkolab and published by . This book was released on 1982 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Modelling of Lower Hybrid RF Heating and Current Drive Experiments in the Alcator C Tokamak written by P. T. Bonoli and published by . This book was released on 1987 with total page 49 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book ERDA Energy Research Abstracts written by and published by . This book was released on 1983 with total page 1144 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Energy Confinement Studies of Lower Hybrid Current Driven Discharges in the Alcator C Tokamak written by S. F. Knowlton and published by . This book was released on 1985 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Energy Confinement Studies of Lower Hybrid Current Driven Plasmas in the Alcator C Tokamak written by Yuichi Takase and published by . This book was released on 1986 with total page 54 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1986 with total page 1040 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Lower Hybrid Heating and Current Drive and Ion Cyclotron Heating Experiments on the Alcator C and the Versator II Tokamaks written by Alcator Group and published by . This book was released on 1984 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt:
