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 Spectrum and Propagation of Lower Hybrid Waves in the Alcator C Tokamak written by R. L. Watterson and published by . This book was released on 1984 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Radio Frequency Edge Physics on the Alcator C Mod Tokamak written by James Christian Reardon and published by . This book was released on 1999 with total page 152 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 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 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 Engineering Aspects of Lower Hybrid Microwave Injection Into the Alcator C Tokamak written by Jack Jerome Schuss and published by . This book was released on 1983 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Investigation of Full wave Effects on Lower hybrid Wave Propagation Absorption and Current Drive written by Samuel Frank (Nuclear engineer) and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lower hybrid current drive (LHCD) has been used as a radio-frequency (RF) heating and current drive actuator in tokamaks for over 40 years. However, despite being one of the first experimentally demonstrated sources of RF current drive, LHCD has never been consistently predicted by numerical simulation using coupled raytracing Fokker-Planck (FP) models. One frequently cited source of this discrepancy is the breakdown of the WKB approximation raytracing is based upon and "full-wave" effects such as diffraction and interference which raytracing cannot resolve. However, this claim has never been thoroughly investigated. In this work, we replace the raytracing model for wave propagation and damping in LHCD simulations with TORLH, a semi-spectral full-wave model that directly solves for the wave fields in order to assess the validity of raytracing. Using groundbreaking TORLH simulations, we demonstrate that in most modern tokamak core scenarios LHCD raytracing/FP calculations closely match full-wave/FP results. We found that previous discrepancies between raytracing and full-wave results in many cases can be attributed to improper controls and a lack of self-consistency in the full-wave/FP iteration. Our simulations of Alcator C-Mod, DIII-D, and the Experimental Advanced Superconducting Tokamak (EAST), suggest full wave effects are unlikely to be of particular importance in reactor-like scenarios where the LH wave is single pass damped, or even in modern experiments where the lower-hybrid wave is weakly damped.

Download or read book Lower Hybrid Heating Experiments on the Alcator C and the Versator II Tokamaks written by Alcator C Group and published by . This book was released on 1982 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Transport of Particles and Energy in the Edge Plasma of the Alcator C Mod Tokamak written by Maxim V. Umansky and published by . This book was released on 1999 with total page 131 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Frequency Density and Spectrum Considerations for Lower hybrid Wave Absorption in the Tokamak de Varennes written by I. P. Shkarofsky and published by . This book was released on 1988 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Edge Turbulence Imaging in the Alcator C Mod Tokamak written by S. J. Zweben and published by . This book was released on 2001 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Lower hybrid heating Experiments on the Alcator C and the Versator II Tokamaks written by and published by . This book was released on 1982 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Initial results are reported from lower hybrid wave heating experiments carried out on the MIT Alcator C and Versator II tokamaks. In the Alcator C experiments a 4 waveguide array, with internally brazed ceramic windows has been used to inject 160 kW of microwave power at 4.6 GHz into the plasma with n0 less than or equal to 1 x 1015 cm−3, and B0 less than or equal to 12 T. An RF power density of 8 kW/cm2 has been transmitted into the plasma without RF breakdown. RF coupling studies show optimal coupling (R less than or equal to 10%) when the local density at the waveguide mouth is 25 to 50 times overdense. Initial heating experiments show an ion tail formation in hydrogen discharge peaking at a density of anti n approx. = 2.7 x 1014 cm−3 at B = 8.9 T, and bulk ion heating at a density of anti n approx. = 1.5 x 1014 c−3 at B approx. = 11 T. Evidence of RF current enhancement has been observed at a density of n approx. = 3 x 1013 cm−3. In the Versator II tokamak initial ion heating studies have been carried out using an 800 MHz, 140 kW klystron. With 50 kW of net RF power injected through a 4 waveguide grill at B = 1.3 T and anti n = 2.5 x 1013 cm−3, Doppler broadening of the OVII and NVI lines shows a .delta.T/sub i/ = 50 eV rise in the bulk ion temperature. A significant RF produced ion tail is also observed by charge exchange analysis. We have succeeded in combining a toroidal ray-tracing code and a 1-D transport code to study the heating density bands and heating efficiencies.

Download or read book Doppler Measurements in the Edge of the Alcator C Mod Tokamak Using a High resolution Visible Spectrometer written by Alexander Turner Graf and published by . This book was released on 2008 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Behavior of Lower Hybrid Waves in the Scrape Off Layer of a Diverted Tokamak written by Gregory M. Wallace and published by . This book was released on 2010 with total page 245 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) Bremsstrahlung emission and relativistic electron cyclotron emission from fast electrons in the core plasma drop suddenly above line averaged densities of 10^20 m^-3, well below the previously observed density limit. These experimental data are compared to both conventional modeling, which gives poor agreement with experiment above the density limit, and a model including edge collisional absorption, which dramatically improves agreement with experiment above the density limit. Combined together, these results show that strong absorption of LH waves in the SOL is possible on a high density tokamak. The paradigm of computationally treating the plasma core and edge as two separate regions with no or weak interaction fails when compared with the C-Mod results. These observations have spurred a shift towards simulating the core and SOL plasma together in predictive simulations of LHCD.

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 High Resolution Edge Thomson Scattering Measurements of the Alcator C Mod Tokamak written by Jerry Wayne Hughes and published by . This book was released on 2000 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: