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Effects of anomalous transport on lower hybrid electron heating

Description: The transport of electron energy out of tokamaks is known to be far greater than that calculated using classical and neoclassical theory. However, low levels of non-axisymmetric magnetic field turbulence can couple the fast transport of electrons parallel to the magnetic field lines to radial transport, thus providing a plausible explanation for observed energy confinement. These models further predict that the electron loss rate is proportional to v/sub parallel bars/. This has subsequently been found to be consistent with data for runaway electrons in PLT, at energies up to 1 MeV. Recently it has been pointed out by Chan, Chiu and Ohkawa that anomalous transport processes should be taken into account in attempting to determine steady state electron distribution functions for cases involving RF electron tail heating, particularly in view of the v/sub parallel bars/ dependence of the loss rate. In this work these physical processes are modeled through a 2-D nonlinear program which describes the evolution of the electron distribution function in velocity magnitude; (v) and plasma radius (r), and which studies the efficiency of tail electron heating.
Date: February 1, 1981
Creator: McCoy, M.G. & Harvey, R.W.
Partner: UNT Libraries Government Documents Department

Three-dimensional simulations of electron cyclotron heating

Description: Many heating problems in tokamaks are inherently three dimensional, involving the velocity coordinates parallel and perpendicular to the ambient magnetic field and the plasma radial coordinate. We will describe a new three-dimensional, Fokker-Planck/rf quasilinear code. This code is based upon a two-dimensional in velocity space Fokker-Planck code which solves for the distribution evaluated at the outer equatorial plane (theta = 0) of each flux surface in a radial mesh.
Date: August 1, 1985
Creator: McCoy, M.G.; Kerbel, G.D. & Harvey, R.W.
Partner: UNT Libraries Government Documents Department

Revisiting the Cape Cod Bacteria Injection Experiment Using a Stochastic Modeling Approach

Description: Bromide and resting-cell bacteria tracer tests carried out in a sand and gravel aquifer at the USGS Cape Cod site in 1987 were reinterpreted using a three-dimensional stochastic approach and Lagrangian particle tracking numerical methods. Bacteria transport was strongly coupled to colloid filtration through functional dependence of local-scale colloid transport parameters on hydraulic conductivity and seepage velocity in a stochastic advection-dispersion/attachment-detachment model. Information on geostatistical characterization of the hydraulic conductivity (K) field from a nearby plot was utilized as input that was unavailable when the original analysis was carried out. A finite difference model for groundwater flow and a particle-tracking model of conservative solute transport was calibrated to the bromide-tracer breakthrough data using the aforementioned geostatistical parameters. An optimization routine was utilized to adjust the mean and variance of the lnK field over 100 realizations such that a best fit of a simulated, average bromide breakthrough curve is achieved. Once the optimal bromide fit was accomplished (based on adjusting the lnK statistical parameters in unconditional simulations), a stochastic particle-tracking model for the bacteria was run without adjustments to the local-scale colloid transport parameters. Good predictions of the mean bacteria breakthrough data were achieved using several approaches for modeling components of the system. Simulations incorporating the recent Tufenkji and Elimelech [1] equation for estimating single collector efficiency were compared to those using the Rajagopalan and Tien [2] model. Both appeared to work equally well at predicting mean bacteria breakthrough using a constant mean bacteria diameter for this set of field conditions, with the Rajagopalan and Tien model yielding approximately a 30% lower peak concentration and less tailing than the Tufenkji and Elimelech formulation. Simulations using a distribution of bacterial cell diameters available from original field notes yielded a slight improvement in the model and data agreement compared to simulations using an ...
Date: November 22, 2006
Creator: Maxwell, R M; Welty, C & Harvey, R W
Partner: UNT Libraries Government Documents Department

Lower hybrid accessibility in a large, hot reversed field pinch

Description: Accessibility and damping of the slow wave in a reversed field pinch (RFP) plasma is investigated theoretically, using projected Reversed Field Experiment (RFX) plasma parameters. By numerically solving the hot plasma dispersion relation, regions of propagation are found and the possibility of mode conversion is analyzed. If the parallel index of refraction of the wave is chosen judiciously at the edge of the plasma, the slow wave is accessible to a target region located just inside the reversal surface without mode conversion. Landau damping is also optimized in this region. A representative fast electron population is then added in order to determine its effect on accessibility and damping. The presence of these electrons, whose parameters were estimated by extrapolation of Madison Symmetric Torus (MST) data, does not affect the accessibility of the wave. However, the initial phase velocity of the wave needs to be increased somewhat in order to maintain optimal damping in the target zone.
Date: November 1, 1995
Creator: Dziubek, R. A.; Harvey, R. W.; Hokin, S. A. & Uchimoto, E.
Partner: UNT Libraries Government Documents Department

Interaction of fast waves with ions

Description: To fully utilize the available power sources in DIII-D (FW, NBI, ECH), understanding of the synergism between the heating mechanisms is important. In this paper the ion distribution, under simultaneous application of NBI and FW, is calculated from Fokker-Planck code CQL3D coupled to ray-tracing code CURRAY. It is found that interaction between energetic ions and FW can be minimized or maximized by adjusting various parameters such as magnetic field, density, beam energy, and FW frequency. Specifically, in DIII-D, the authors find negligible interactions above 1.8 T and above 80 MHz, while the interaction increases at lower fields and frequencies. The results are compared with experiments in DIII-D including the calculated neutron rate. Energetic ion orbit losses may play an important role in the ion distribution, and this effect is being investigated.
Date: June 1, 1995
Creator: Chiu, S.C.; deGrassie, J.S. & Harvey, R.W.
Partner: UNT Libraries Government Documents Department

RADIAL TRANSPORT EFFECTS ON ECCD IN THE TCV AND DIII-D TOKAMAKS AND ON OHMIC DISCHARGES IN THE MST RFP

Description: The comprehensive CQL3D Fokker-Planck/Quasilinear simulation code has been benchmarked against experiment over a wide range of electron cyclotron conditions in the DIII-D tokamak (C.C. Petty et al., 14th Topical Conf. on RF Power in Plasmas, 2002). The same code, in disagreement with experiment, gives 560 kA of ECCD for a well documented, completely ECCD-driven, 100 kA TCV shot [O. Sauter et al, PRL, 2000]. Recent work (R.W. Harvey et al, Phys. Rev. Lett., 2002) has resolved the differences as due to radial transport at a level closely consistent with ITER scaling. Transport does not substantially affect DIII-D ECCD, but at similar ECH power has an overwhelming effect on the much smaller TCV. The transport is consistent with electrostatic-type diffusion (D{sub {rho}{rho}} constant in velocity-space) and not with a magnetic-type diffusion (D{sub {rho}{rho}} {proportional_to} |v{parallel}|). Fokker-Planck simulation of Ohmic reversed field pinch (RFP) discharges in the MST device reveals transport velocity dependence stronger than |v{parallel}| will give agreement with current and soft X-ray spectra in standard discharges, but in the higher confinement, current profile controlled PPCD discharges, transport is again electrostatic-like. This is consistent with the object of PPCD, which is to replace magnetic turbulence driven current with auxiliary CD to improve transport. The tokamak and high-confinement RFP results mutually reinforce the constant-in-velocity-space ''electrostatic-type turbulence'' conclusion. The steady-state energy and toroidal current are governed by the same radial transport equation.
Date: July 1, 2002
Creator: HARVEY, R.W.; SAUTER, O.; PRATER, R.; NIKKOLA, P.; O'CONNELL, R. & FOREST, C.B.
Partner: UNT Libraries Government Documents Department

EBW-Bootstrap Current Synergy in the National Spherical Torus Experiment (NSTX)

Description: Current driven by electron Bernstein waves (EBW) and by the electron bootstrap effect are calculated separately and concurrently with a kinetic code, to determine the degree of synergy between them. A target {beta} = 40% NSTX plasma is examined. A simple bootstrap model in the CQL3D Fokker-Planck code is used in these studies: the transiting electron distributions are connected in velocity-space at the trapped-passing boundary to trapped-electron distributions which are displaced radially by a half-banana width outwards/inwards for the co-/counter-passing regions. This model agrees well with standard bootstrap current calculations, over the outer 60% of the plasma radius. Relatively small synergy net bootstrap current is obtained for EBW power up to 4 MW. Locally, bootstrap current density increases in proportion to increased plasma pressure, and this effect can significantly affect the radial profile of driven current.
Date: February 2, 2005
Creator: Harvey, R.W. & Taylor, G.
Partner: UNT Libraries Government Documents Department

Altitude starting characteristics of an afterburner with autoignition and hot-streak ignition

Description: From Introduction: "Ignition of the fuel-air mixture in an afterburner of turbojet engine at altitude has often proved to be a different problem to solve. Electrical ignition has not proven satisfactory because of the unreliability of such systems (ref. 1). The ignition data reported herein were obtained for two after-burner configurations. Autoignition data are included for both configurations and hot-streak-ignition data, for only one. "
Date: April 6, 1953
Creator: Renas, P E; Jansen, E T & Harvey, R W , Sr
Partner: UNT Libraries Government Documents Department

ECRH/EBWH SYSTEM FOR NSTX-

Description: The National Spherical Torus Experiment Upgrade (NSTX-U) will operate at an axial toroidal field of up to 1 T, about twice the field available on NSTX. A 28 GHz electron cylotron resonance heating (ECRH) system is currently being planned for NSTX-U. A 1 MW 28 GHz gyrotron will be employed. Intially the system will use short, 10-50 ms, 1 MW pulses for ECRH-assisted discharge start-up. Later the pulse length will be extended to 1-5 s to study electron Bernstein wave heating (EBWH) during the plasma current flat top. A mirror launcher will be used to couple microwave power to the plasma via O-mode to the slow X-mode to EBW (O-X-B) double mode conversion. This paper presents a pre-conceptual design for the ECRH/EBWH system proposed for NSTX-U and includes ray tracing and Fokker-Planck modeling results for 28 GHz ECRH during plasma start-up and EBW heating and current drive during the plasma current flattop of a NSTX-U advanced H-mode plasma scenario.
Date: June 15, 2012
Creator: Taylor, G.; Ellis, R. A.; Harvey, R. W.; Hosea, J. C. & Smirnov, A. P.
Partner: UNT Libraries Government Documents Department

Long Pulse High Performance Plasma Scenario Development for the National Spherical Torus Experiment

Description: The National Spherical Torus Experiment [Ono et al., Nucl. Fusion, 44, 452 (2004)] is targeting long pulse high performance, noninductive sustained operations at low aspect ratio, and the demonstration of nonsolenoidal startup and current rampup. The modeling of these plasmas provides a framework for experimental planning and identifies the tools to access these regimes. Simulations based on neutral beam injection (NBI)-heated plasmas are made to understand the impact of various modifications and identify the requirements for (1) high elongation and triangularity, (2) density control to optimize the current drive, (3) plasma rotation and/or feedback stabilization to operate above the no-wall limit, and (4) electron Bernstein waves (EBW) for off-axis heating/current drive (H/CD). Integrated scenarios are constructed to provide the transport evolution and H/CD source modeling, supported by rf and stability analyses. Important factors include the energy confinement, Zeff, early heating/H mode, broadening of the NBI-driven current profile, and maintaining q(0) and qmin>1.0. Simulations show that noninductive sustained plasmas can be reached at IP=800 kA, BT=0.5 T, 2.5, N5, 15%, fNI=92%, and q(0)>1.0 with NBI H/CD, density control, and similar global energy confinement to experiments. The noninductive sustained high plasmas can be reached at IP=1.0 MA, BT=0.35 T, 2.5, N9, 43%, fNI=100%, and q(0)>1.5 with NBI H/CD and 3.0 MW of EBW H/CD, density control, and 25% higher global energy confinement than experiments. A scenario for nonsolenoidal plasma current rampup is developed using high harmonic fast wave H/CD in the early low IP and low Te phase, followed by NBI H/CD to continue the current ramp, reaching a maximum of 480 kA after 3.4 s.
Date: January 1, 2006
Creator: Kessel, C.E.; Bell, R.E.; Bell, M.G.; Gates, D.A. & Harvey, R.W.
Partner: UNT Libraries Government Documents Department

Te (R,t) Measurements using Electron Bernstein Wave Thermal Emission on NSTX

Description: The National Spherical Torus Experiment (NSTX) routinely studies overdense plasmas with ne of (1–5) X 1019 m-3 and total magnetic field of <0.6 T, so that the first several electron cyclotron harmonics are overdense. The electrostatic electron Bernstein wave (EBW) can propagate in overdense plasmas, exhibits strong absorption, and is thermally emitted at electron cyclotron harmonics. These properties allow thermal EBW emission to be used for local Te measurement. A significant upgrade to the previous NSTX EBW emission diagnostic to measure thermal EBW emission via the oblique B-X-O mode conversion process has been completed. The new EBW diagnostic consists of two remotely steerable, quad-ridged horn antennas, each of which is coupled to a dual channel radiometer. Fundamental (8–18 GHz) and second and third harmonic (18–40 GHz) thermal EBW emission and polarization measurements can be obtained simultaneously.
Date: June 9, 2006
Creator: Diem, S J; Efthimion, P C; LeBlanc, B P; Carter, M; Caughman, J; Wilgen, J B et al.
Partner: UNT Libraries Government Documents Department

Refractive and Relativistic Effects on ITER Low Field Side Reflectometer Design

Description: The ITER low field side reflectometer faces some unique design challenges, among which are included the effect of relativistic electron temperatures and refraction of probing waves. This paper utilizes GENRAY, a 3- D ray tracing code, to investigate these effects. Using a simulated ITER operating scenario, characteristics of the reflected RF waves returning to the launch plane are quantified as a function of a range of design parameters, including antenna height, antenna size, and antenna radial position. Results for edge/SOL measurement with both O- and X-modes using proposed antennas are reported.
Date: June 1, 2010
Creator: Wang, G.; Rhodes, T. L.; Peebles, W. A.; Harvey, R. W. & Budny, R. V.
Partner: UNT Libraries Government Documents Department

Measurements of optically thin electron cyclotron emission from relativistic electrons

Description: Electron cyclotron emission (ECE) from hot, relativistic electrons has been measured simulataneously at several optically thin frequencies (f/f/sub ce/ = 4.6, 7.0, and 9.6) on the Tandem Mirror Experiment-Upgrade. A method to determine the temporal evolution of the hot electron density, n/sub h/, and temperature T/sub h/ is discussed. Calculations of T/sub h/ agree with the analysis of the high energy x-ray spectra. Heating rates vary between 3 keV/ms and 13 keV/ms and temperatures over 300 keV have been reached by the end of the 50 ms discharge. The ECE analysis provides an order of magnitude improvement in time resolution over the x-ray analysis and shows that fast reductions in the diamagnetic loop signals are predominantly a loss of perpendicular energy stored by the mirror trapped hot electrons. These techniques for determining n/sub h/(t) and T/sub t/(t) will be used on the DIII-D tokamak in order to parameterize the nonthermal electron tail produced during ECH current drive experiments. A vertical view will be utilized and a fast (70 Hz) scanning Michelson interferometer will be used to measure the ECE spectrum between the 2nd and the 15th harmonic. 11 refs., 7 figs.
Date: October 1, 1987
Creator: James, R.A.; Silver, E.; Boyd, D.; Ellis, R.F.; Jantz, S.; Lasnier, C.J. et al.
Partner: UNT Libraries Government Documents Department

A design study for the ECH launcher for ITER

Description: The Design Description Document for ITER calls for 50 MW of electron cyclotron power at a frequency of 170 GHz, upgradeable to 100 MW. This power is intended to heat the plasma from Ohmic temperatures to ignition, in concert with power from some combination of neutral injection and/or ICRF heating. The second major application of ECH power is current drive. In the advanced steady-state scenarios, the total current is 12 to 16 MA, of which 75% is driven by bootstrap effects. The current drive requirement is 2 to 3 MA at a relative minor radius of 0.7, plus a small current near the center of the discharge. ECH power is also used for plasma initiation and startup, using a separate ECH system of two fixed frequencies between 90 to 140 GHz and total power to 6 MW. Suppression or control of MHD instabilities like neoclassical tearing modes, sawteeth, ELMs, and locked modes are also important objectives for the ECH systems. However, the launching and power characteristics of the ECH for these applications is highly specialized. The ability to modulate at high frequency (at least several tens of kHz), the ability to redirect the beams with precision at relatively high speed, and the requirement that the stabilization be carried out at the same time as the bulk heating and current drive imply that separate and specialized ECH systems are needed for the stabilization activities. For example, for stabilization of neoclassical tearing modes current must be driven inside the islands near the q = 2 surface. If this is done near the outboard mid plane, a system with optimized frequency might be much more effective than what could be done with the main 170 GHz system. This paper does not treat the launchers for the stabilization systems.
Date: April 1, 1997
Creator: Prater, R.; Grunloh, H.J.; Moeller, C.P.; Doane, J.L.; Olstad, R.A.; Makowski, M.A. et al.
Partner: UNT Libraries Government Documents Department

Modeling of Trapped Electron Effects on Electron Cyclotron Current Drive for Recent DIII-D Experiments

Description: Owing to its potential capability of generating localized non-inductive current, especially off-axis, Electron Cyclotron Current Drive (ECCD) is considered a leading candidate for current profile control in achieving Advanced Tokamak (AT) operation. In recent DIII-D proof-of-principle experiments [1], localized off-axis ECCD has been clearly demonstrated for first time. The measured current drive efficiency near the magnetic axis agrees well with predictions of the bounce-averaged Fokker-Planck theory [2,3]. However, the off-axis current drive efficiency was observed to exceed the theoretical results, which predict significant degradation of the current drive efficiency due to trapped electron effects. The theoretical calculations have been based on an assumption that the effective collision frequency is much smaller than the bounce frequency such that the trapped electrons are allowed to complete the banana orbit at all energies. The assumption might be justified in reactor-grade tokamak plasmas, in which the electron temperature is sufficiently high or the velocity of resonant electrons is much larger than the thermal velocity, so that the influence of collisionality on current drive efficiency can be neglected. For off-axis deposition in the present-day experiments, the effect of high density and low temperature is to reduce the current drive efficiency, but the increasing collisionality reduces the trapping of current-carrying electrons, leading to compensating increases in the current drive efficiency. In this work, we use the adjoint function formulation [4] to examine collisionality effects on the current drive efficiency.
Date: August 1999
Creator: Lin-Liu, Y. R.; Sauter, O.; Harvey, R. W.; Chan, V. S.; Luce, T. C. & Prater, R.
Partner: UNT Libraries Government Documents Department

Electron cyclotron heating and current drive: Present experiments to ITER

Description: Electron cyclotron (EC) power has technological and physics advantages for heating and current drive in a tokamak reactor, and advances in source development make it credible for applications in ITER. Strong single pass absorption makes heating to ignition particularly simple. The optimized EC current drive (ECCD) efficiency (<n>IR/P) shows a linear temperature scaling at temperatures up to {approximately}15 keV. For temperatures above 30 keV, the efficiency saturates at approximately 0.3{center_dot}10{sup 20} A/(m{sup 2}W) for a frequency of 220 GHz in an ITER target plasma with toroidal field of 6 T, due primarily to harmonic overlap and to a lesser extent due to limitations arising from relativistic effects. The same efficiency can also be obtained at 170 GHz for the same plasma equilibrium except that the magnetic field is reduced to (170/200) {times} 6 T = 4.6 T. The ECCD efficiencies are obtained with the comprehensive 3D, bounce-averaged Fokker-Planck CQL3D codes and BANDIT3D.
Date: August 1, 1995
Creator: Harvey, R.W.; Nevins, W.M.; Smith, G.R.; Lloyd, B.; O`Brien, M.R. & Warrick, C.D.
Partner: UNT Libraries Government Documents Department

Electron cyclotron heating and current drive: Present experiments to ITER. Revision 1

Description: Electron cyclotron (EC) power has technological and physics advantages for heating and current drive in a tokamak reactor, and advances in source development make it credible for applications in ITER. Strong single pass absorption makes heating to ignition particularly simple. The optimized EC current drive (ECCD) efficiency ({l_angle}n{r_angle}IR/P) shows a linear temperature scaling at temperatures up to {approximately} 15 keV. For temperatures above 30 keV, the efficiency saturates at approximately 0.3{center_dot}10{sup 20} A/(m{sup 2}W) for a frequency of 220 GHz in an ITER target plasma with toroidal field of 6 T, due primarily to harmonic overlap [G.R. Smith et al., Phys. Fluids 30 3633 (1987)] and to a lesser extent due to limitations arising from relativistic effects [N.J. Fisch, Phys. Rev. A 24 3245 (1981)]. The same efficiency can also be obtained at 170 GHz for the same plasma equilibrium except that the magnetic field is reduced to (170/220) {times} 6 T = 4.6 T. The ECCD efficiencies are obtained with the comprehensive 3D, bounce-averaged Fokker-Planck CQL3D codes [R.W. Harvey and M.G. McCoy, Proc. IAEA TCM/Advances in Simulation and Modeling in Thermonuclear Plasmas 1992, Montreal], and BANDIT3D [M.R. O`Brien, M. Cox, C.D. Warrick, and F. S. Zaitsev, ibid.].
Date: August 1, 1995
Creator: Harvey, R.W.; Nevins, W.M.; Smith, G.R.; Lloyd, B.; O`Brien, M.R. & Warrick, C.D.
Partner: UNT Libraries Government Documents Department

DETAILED MEASUREMENTS OF THE ELECTRON CYCLOTRON CURRENT DRIVE EFFICIENCY ON DIIID

Description: Electron cyclotron current drive (ECCD) experiments on the DIII-D tokamak are solidifying the physics basis for localized, off-axis current drive, the goal being to validate a predictive model for ECCD. The ECCD profiles are determined from the magnetic field pitch angles measured by motional Stark effect (MSE) polarimetry. The measured ECCD switches from the co to the counter direction as the toroidal injection angle is varied with a profile width that is in accordance with ray tracing calculations. Tests of electron trapping in low beta plasmas show that the ECCD efficiency decreases rapidly as the deposition is moved off-axis and towards the outboard side of the plasma, but the detrimental effects of electron trapping on the current drive are greatly reduced in high beta plasmas. Overall, the measured ECCD is in good agreement with theoretical calculations using a quasilinear Fokker-Planck code over a wide range of injection angles and plasma parameters.
Date: May 1, 2002
Creator: PETTY, C.C.; PRATER, R.; LOHR, J.; LUCE, T.C.; FOX,W.R.; HARVEY, R.W. et al.
Partner: UNT Libraries Government Documents Department

Modeling of fast wave current drive experiments on DIII-D

Description: Modeling of fast wave current drive experiments for D3-D has been improved to include calculation of target temperature profiles consistent with the D3-D database and more accurate modeling of the launched spectrum. The calculations indicate that a measurable current will be driven by fast wave in the near-term (30--200 kA). Modeling of the long-range goal of 2 MA non-inductive at high {beta} indicates the proposed 18 MW of rf power will be adequate. The optimum frequency for the intermediate scenario is 120 MHz; this frequency selection is also adequate for the long-term goals. 8 refs., 2 figs., 2 tabs.
Date: September 1, 1991
Creator: Luce, T.C.; Chiu, S.C.; Harvey, R.W.; Mayberry, M.J.; Petty, C.C.; Pinsker, R.I. et al.
Partner: UNT Libraries Government Documents Department

Physics Design of a 28 GHz Electron Heating System for the National Spherical Torus Experiment Upgrade

Description: A megawatt-level, 28 GHz electron heating system is being designed to support non-inductive (NI) plasma current (I{sub p}) start-up and local heating and current drive (CD) in H-mode discharges in the National Spherical Torus Experiment Upgrade (NSTX-U). The development of fully NI I{sub p} start-up and ramp-up is an important goal of the NSTX-U research program. 28 GHz electron cyclotron (EC) heating is predicted to rapidly increase the central electron temperature (T{sub e}(0)) of low density NI plasmas generated by Coaxial Helicity Injection (CHI). The increased T{sub e}(0) will significantly reduce the Ip decay rate of CHI plasmas, allowing the coupling of fast wave heating and neutral beam injection. Also 28 GHz electron Bernstein wave (EBW) heating and CD can be used during the I{sub p} flat top in NSTX-U discharges when the plasma is overdense. Ray tracing and Fokker-Planck numerical simulation codes have been used to model EC and EBW heating and CD in NSTX-U. This paper presents a pre-conceptual design for the 28 GHz heating system and some of the results from the numerical simulations.
Date: July 9, 2013
Creator: Taylor, G.; Bertelli, N.; Ellis, R. A.; Gerhardt, S. P.; Harvey, R. W.; Hosea, J. C. et al.
Partner: UNT Libraries Government Documents Department

The Effects of the Scattering by Edge Plasma Density Fluctuations on Lower Hyybrid Wave Propagation

Description: Scattering effects induced by edge density fluctuations on lower hybrid (LH) wave propagation are investigated. The scattering model used here is based on the work of Bonoli and Ott [Phys. Fluids 25 (1982) 361]. It utilizes an electromagnetic wave kinetic equation solved by a Monte Carlo technique. This scattering model has been implemented in GENRAY , a ray tracing code which explicitly simulates wave propagation, as well as collisionless and collisional damping processes, over the entire plasma discharge, including the scrape-off layer (SOL) that extends from the separatrix to the vessel wall. A numerical analysis of the LH wave trajectories and the power deposition profile with and without scattering is presented for Alcator CMod discharges. Comparisons between the measured hard x-ray emission on Alcator C-Mod and simulations of the data obtained from the synthetic diagnostic included in the GENRAY/CQL3D package are shown, with and without the combination of scattering and collisional damping. Implications of these results on LH current drive are discussed.
Date: August 27, 2012
Creator: Bertelli, N.; Bonoli, P. T.; Harvey, R. W.; Smirnov, A. P.; Baek, S. G.; Parker, R. R. et al.
Partner: UNT Libraries Government Documents Department

Investigation of EBW Thermal Emission and Mode Conversion Physics in H-Mode Plasmas on NSTX

Description: High β plasmas in the National Spherical Torus Experiment (NSTX) operate in the overdense regime, allowing the electron Bernstein wave (EBW) to propagate and be strongly absorbed/emitted at the electron cyclotron resonances. As such, EBWs may provide local electron heating and current drive. For these applications, efficient coupling between the EBWs and electromagnetic waves outside the plasma is needed. Thermal EBW emission (EBE) measurements, via oblique B-X-O double mode conversion, have been used to determine the EBW transmission efficiency for a wide range of plasma conditions on NSTX. Initial EBE measurements in H-mode plasmas exhibited strong emission before the L-H transition, but the emission rapidly decayed after the transition. EBE simulations show that collisional damping of the EBW prior to the mode conversion (MC) layer can significantly reduce the measured EBE for Te &lt; 20 eV, explaining the observations. Lithium evaporation was used to reduce EBE collisional damping near the MC layer. As a result, the measured B-X-O transmission efficiency increased from &lt; 10% (no Li) to 60% (with Li), consistent with EBE simulations.
Date: March 20, 2008
Creator: Diem, S. J.; Efthimion, P. C.; Kugel, H. W.; LeBlanc, B. P.; Phillips, C. K.; Caughman, J. B. et al.
Partner: UNT Libraries Government Documents Department