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Design of microwave vitrification systems for radioactive waste

Description: Oak Ridge National Laboratory (ORNL) is involved in the research and development of high-power microwave heating systems for the vitrification of Department of Energy (DOE) radioactive sludges. Design criteria for a continuous microwave vitrification system capable of processing a surrogate filtercake sludge representative of a typical waste-water treatment operation are discussed. A prototype 915-MHz, 75-kW microwave vitrification system or ``microwave melter`` is described along with some early experimental results that demonstrate a 4 to 1 volume reduction of a surrogate ORNL filtercake sludge.
Date: December 31, 1995
Creator: White, T.L.; Wilson, C.T.; Schaich, C.R. & Bostick, T.L.
Partner: UNT Libraries Government Documents Department

Combline antenna modeling for plasma heating

Description: The combline antenna for plasma heating, as proposed by General Atomics, has unique potential for solving many plasma drive problems. The benefit of the combline design is the utilization of the coupling between elements that avoids a more cumbersome multidrive system. This design is being investigated using computational EM modeling codes in the 100-400 MHz band using resources at General Atomics and LLNL. Preliminary experimental results, using a combline mockup, agree well with 3D modeling efforts including resonant frequency alignment and amplitudes. These efforts have been expanded into an endeavor to optimize the combline design using both time and frequency domain codes. This analysis will include plasma coupling but to date has been limited to antenna effects. The combline antenna system is modeled in 3D using a combination of computational tools in the time domain, for temporal feature isolation purposes, and in the frequency domain, for resonant structure analysis. Both time and frequency domain modeling details include the Faraday shield elements, the strap elements, and the feed structure.
Date: May 15, 1995
Creator: Nelson, S.D.; Kamin, G. & Van Maren, R.
Partner: UNT Libraries Government Documents Department

R.F. heating near the lower hybrid frequency in the FM-1 spherator

Description: Plasma heating experiments at frequencies near the lower hybrid frequency have been carried out at modest powers (.05 to 4kW). The antenna structure operating at 68 MHz was comprised of two plates driven out of phase on the exterior of the plasma. High electron heating efficiency (greater than 40 percent) in both helium and argon plasmas was observed with only a weak density dependence. At low densities (n/sub e/ less than or equal to 1 x 10$sup 11$ cm$sup -3$), the heating was uniform across the plasma while at higher densities the heating was preferentially on the exterior portion of the plasma. The heating of the exterior of the plasma was found not to correspond to absorption at the lower hybrid resonance layer. The electron heating efficiency was found to be a weak function of rf power when the incident rf power was varied from 1 to 15 times the experimentally observed threshold power for parametric instabilities. Ion temperatures were determined by measuring the Doppler broadening of an Argon ion line using a Fabry-Perot interferometer. Low efficiency main body ion heating (1 to 3 percent) was observed. (auth)
Date: December 1, 1975
Creator: Hawryluk, R.J.; Davis, S.L. & Schmidt, J.A.
Partner: UNT Libraries Government Documents Department

Measurements of edge density profile modifications during IBW on TFTR

Description: Ion Bernstein wave (IBW) antennas are known to have substantial localized effects on the plasma edge. To allow better understanding and measurement of these effects, the TFTR edge reflectometer has been relocated to the new IBW antenna. This move was facilitated by the incorporation of a diagnostic access tube in the IBW antenna identical to the original diagnostic tube in the fast-wave (FW) antenna. This allowed the reflectometer launcher to simply be moved from the old FW antenna to the new IBW antenna. Only a moderate extension of the waveguide transmission line was required to reconnect the reflectometer to the launcher in its new location. Edge density profile modification during IBW experiments has been observed. Results from IBW experiments will be presented and contrasted to the edge density modifications previously observed during FW heating experiments.
Date: June 1, 1997
Creator: Hanson, G. R.; Bush, C. E. & Wilgen, J. B.
Partner: UNT Libraries Government Documents Department

Applications of fast wave in spherical tokamaks

Description: In spherical tokamaks (ST), the magnetic field strength varies over a wide range across the plasma, and at high betas it deviates significantly from the 1/R dependence of conventional tokamaks. This, together with the high density expected in ST, poses challenging problems for RF heating and current drive. In this paper, the authors investigate the various possible applications of fast waves (FW) in ST. The adjoint technique of calculating current drive is implemented in the raytracing code CURRAY. The applicability of high harmonic and subharmonic FW to steady state ST is considered. They find that high harmonic FW tends to be totally absorbed before reaching the core and may be considered a candidate for off axis current drive while the subharmonic FW tends to be absorbed mainly in the core region and may be considered for central current drive. A difficult problem is the maintenance of current at the startup stage. In the bootstrap ramp-up scenario, the current ramp-up is mainly provided by the bootstrap current. Under this condition, the role of rf becomes mainly the sustainment of plasma through electron heating. Using a slab full-wave code SEMAL, the authors find that the ion-ion-hybrid mode conversion scheme is a promising candidate. The effect of possible existence of edge Alfven resonance and high harmonic cyclotron resonance is investigated and regimes of minimization of edge heating identified.
Date: April 1, 1997
Creator: Chiu, S.C.; Chan, V.S.; Lin-Liu, Y.R.; Miller, R.L.; Prater, R. & Politzer, P.
Partner: UNT Libraries Government Documents Department

High-harmonic fast wave heating experiments in CDX-U

Description: One of the primary objectives of the proposed National Spherical Tokamak Experiment (NSTX) is the investigation of very high {beta} regimes. Consequently, finding efficient methods of non-inductive heating and current drive required to heat and sustain such plasmas is of considerable importance. High-frequency fast waves are a promising candidate in this regard. However, in NSTX, the field-line pitch at the outer midplane will range from 0 up to 60 degrees from plasma start-up to current flattop. Thus, antenna strap orientation with respect to the edge magnetic field may have a serious impact on power coupling and absorption. To address this issue, the vacuum vessel of the Current Drive Experiment -- Upgrade (CDX-U) spherical tokamak has been upgraded to accommodate a rotatable two-strap antenna capable of handling several hundred kilowatts in short pulses. Details of the antenna design and results from loading measurements made as a function of power, strap angle, and strap phasing will be presented. Results from microwave scattering experiments will also be discussed.
Date: December 1, 1997
Creator: Menard, J.; Majeski, R.; Ono, M.; Wilson, J.R.; Munsat, T. & Seki, T.
Partner: UNT Libraries Government Documents Department

Continued development of modeling tools and theory for RF heating

Description: Mission Research Corporation (MRC) is pleased to present the Department of Energy (DOE) with its renewal proposal to the Continued Development of Modeling Tools and Theory for RF Heating program. The objective of the program is to continue and extend the earlier work done by the proposed principal investigator in the field of modeling (Radio Frequency) RF heating experiments in the large tokamak fusion experiments, particularly the Tokamak Fusion Test Reactor (TFTR) device located at Princeton Plasma Physics Laboratory (PPPL). An integral part of this work is the investigation and, in some cases, resolution of theoretical issues which pertain to accurate modeling. MRC is nearing the successful completion of the specified tasks of the Continued Development of Modeling Tools and Theory for RF Heating project. The following tasks are either completed or nearing completion. (1) Anisotropic temperature and rotation upgrades; (2) Modeling for relativistic ECRH; (3) Further documentation of SHOOT and SPRUCE. As a result of the progress achieved under this project, MRC has been urged to continue this effort. Specifically, during the performance of this project two topics were identified by PPPL personnel as new applications of the existing RF modeling tools. These two topics concern (a) future fast-wave current drive experiments on the large tokamaks including TFTR and (c) the interpretation of existing and future RF probe data from TFTR. To address each of these topics requires some modification or enhancement of the existing modeling tools, and the first topic requires resolution of certain theoretical issues to produce self-consistent results. This work falls within the scope of the original project and is more suited to the project`s renewal than to the initiation of a new project.
Date: December 1, 1998
Partner: UNT Libraries Government Documents Department

Design of the HHFW heating and current drive system for NSTX

Description: The National Spherical Tokamak Experiment (NSTX) is a low aspect ratio (A = 1.25) tokamak being built at Princeton Plasma Physics Laboratory (PPPL), with major radius = 0.8 m, B{sub T} = 0.32 T and I{sub p} up to 1 MA. The machine requires on the order of 6 MW of auxiliary heating in order to test {beta} limits and it needs electron heating/current drive in order to extend the pulse length and demonstrate non-inductive startup. The high harmonic fast wave (HHFW) system, operating at 30 MHz, is being designed to meet these objectives.
Date: November 1, 1998
Creator: Ryan, P.M.; Carter, M.D. & Swain, D.W.
Partner: UNT Libraries Government Documents Department

Macroscopic time and altitude distribution of plasma turbulence induced in ionospheric modification experiments

Description: This is the final report of a three-year Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This research concentrated on the time dependence of the heater, induced-turbulence, and electron-density profiles excited in the ionosphere by a powerful radio-frequency heater wave. The macroscopic density is driven by the ponderomotive pressure and the density self-consistently determines the heater propagation. For typical parameters of the current Arecibo heater, a dramatic quasi-periodic behavior was found. For about 50 ms after turn-on of the heater wave, the turbulence is concentrated at the first standing-wave maximum of the heater near reflection altitude. From 50--100 ms the standing-wave pattern drops by about 1--2 km in altitude and the quasi-periodicity reappears at the higher altitudes with a period of roughly 50 ms. This behavior is due to the half-wavelength density depletion grating that is set up by the ponderomotive pressure at the maxima of the heater standing-wave pattern. Once the grating is established the heater can no longer propagate to higher altitudes. The grating is then unsupported by the heater at these altitudes and decays, allowing the heater to propagate again and initiate another cycle. For stronger heater powers, corresponding to the Arecibo upgrade and the HAARP heater now under construction, the effects are much more dramatic.
Date: March 1, 1996
Creator: Rose, H.; Dubois, D.; Russell, D. & Hanssen, A.
Partner: UNT Libraries Government Documents Department

Measurement of rf voltages on the plasma-touching surfaces of ICRF antennas

Description: Measurements of the rf voltages on Faraday shields and protection bumpers have been made for several loop antennas, including the mock-up antenna and Al for JET, the original antenna for Tore Supra, the present ASDEX-U antenna, and the folded waveguide. The loop antennas show voltages that scale to {approx}12 kV for a maximum input voltage of 30 kV with 0/0 phasing. The voltages are dramatically reduced for 0/{pi} phasing. These voltages are significant in that they can substantially increase the rf sheath potential beyond the levels associated with the simple electromagnetic field linkage from the current straps that results in plasma heating. In this paper, we investigate and measure the source of these voltages, their scaling with antenna impedance, and the differences between the loop arrays.
Date: September 1995
Creator: Hoffman, D. J.; Baity, F. W.; Bell, G. L.; Bigelow, T. S.; Caughman, J. B. O.; Goulding, R. H. et al.
Partner: UNT Libraries Government Documents Department

Waveguide and loop coupling to fast MHD toroidal eigenmodes

Description: Heating of plasmas by wave techniques requires an effective method of coupling rf energy to the plasma. In cavities the presence of weakly damped eigenmodes will enhance the loading of antennas when the wave frequency equals an eigenmode frequency. This report considers two methods of coupling to fast MHD eigenmodes in a toroidal cavity: one is by a waveguide mounted perpendicular to the vacuum vessel wall; and the other by a loop placed within the cavity. (auth)
Date: December 1, 1975
Creator: Paoloni, F.J.
Partner: UNT Libraries Government Documents Department

Self-consistent microwave plasma heating rates

Description: Under conditions within a hot overdense plasma corona where the field frequency is much less than the electron plasma frequency and the field period is much less than the hydrodynamic expansion time it is shown that electron field reversal heating can exceed the combined classical heating rates due to inverse bremsstrahlung (skin effect) and field pressure (PdV) by a factor approximately v/ sub e//2v/sub i/ (half the ratio of electron and ion thermal velocities). In particular this rate can exceed the inertial expansion cooling rate at a collisionless corona density of approximately 1 percent solid core density and could be realized experimentally at core temperatures approximately 3--5 keV and microwave field intensities approximately 1 MG. (auth)
Date: October 1, 1975
Creator: Ensley, D.L. & White, R.H.
Partner: UNT Libraries Government Documents Department

A high power experimental traveling wave antenna for fast wave heating and current drive in DIII-D and relevance to ITER

Description: The impact of a contemplated conversion of the directly driven high power antenna arrays in DIII-D to externally tuned and coupled traveling wave antennas (TWAs) is evaluated based on empirical modeling, computer simulation and low power experiments. A regime of operation is predicted within the TWA passband in which the reflected power from the TWA approaches 0.1% during ELM-free H-mode. Furthermore, this reflected power does not exceed 1% and the optimum phase velocity produced by the TWA decreases less than 5% during ELMs. This resilient operating regime is phase shifted using external tuning stubs, thus providing considerable experimental flexibility. Over 90% plasma coupling efficiency is achieved by recovering the TWA output power using a novel traveling wave recirculator. Combining the above attributes with efficient plasma coupling even at large antenna-plasma distances and the lack of need for dynamic tuning, TWAs appear to offer great promise for ITER.
Date: October 1, 1995
Creator: Phelps, D.A.; Ikezi, H. & Moeller, C.P.
Partner: UNT Libraries Government Documents Department

Plasma rotation and rf heating in DIII-D

Description: In a variety of discharge conditions on DIII-D it is observed that rf electron heating reduces the toroidal rotation speed and core ion temperature. The rf heating can be with either fast wave or electron cyclotron heating and this effect is insensitive to the details of the launched toroidal wavenumber spectrum. To date all target discharges have rotation first established with co-directed neutral beam injection. A possible cause is enhanced ion momentum and thermal diffusivity due to electron heating effectively creating greater anomalous viscosity. Another is that a counter directed toroidal force is applied to the bulk plasma via rf driven radial current.
Date: May 1, 1999
Creator: deGrassie, J.S.; Baker, D.R. & Burrell, K.H.
Partner: UNT Libraries Government Documents Department

Heating and current drive on NSTX and HHFW experiments on CDX-U

Description: The NSTX (National Spherical Torus Experiment) device to be built at Princeton is a low-aspect-ratio toroidal device that has the achievement of high toroidal beta ({approximately} 45%) and noninductive operation as two of its main research goals. To achieve these goals, significant auxiliary-heating and current-drive systems are required. Present plans include ECH (electron cyclotron heating) for preionized and start-up assist, HHFW (high harmonic fast wave) for heating and current drive, and, eventually, NBI (neutral-beam injection) for heating, current drive and plasma rotation. In support of the NSTX program, experimental tests of HHFW physics have been performed on the Current Drive Experiment-Upgrade (CDX-U).
Date: July 1, 1998
Creator: Wilson, J.R.; Hosea, J. & Grisham, L.
Partner: UNT Libraries Government Documents Department

Experiments on ion cyclotron damping at the deuterium fourth harmonic in DIII-D

Description: Absorption of fast Alfven waves by the energetic ions of an injected beam is evaluated in the DIII-D tokamak. Ion cyclotron resonance absorption at the fourth harmonic of the deuteron cyclotron frequency is observed with deuterium neutral beam injection (f = 60 MHz, B{sub T} = 1.9 T). Enhanced D-D neutron rates are evidence of absorption at the Doppler-shifted cyclotron resonance. Characteristics of global energy confinement provide further proof of substantial beam acceleration by the rf. In many cases, the accelerated deuterons cause temporary stabilization of the sawtooth (monster sawteeth), at relatively low rf power levels of {approximately}1 MW.
Date: May 1, 1999
Creator: Pinsker, R.I.; Petty, C.C.; Baity, F.W.; Bernabei, S.; Greenough, N.; Heidbrink, W.W. et al.
Partner: UNT Libraries Government Documents Department

Radio frequency wave experiments on the MST reversed field pinch

Description: Experiments, simulations, and theory all indicate that the magnetic fluctuations responsible for the poor confinement in the reversed field pinch (RFP) can be controlled by altering the radial profile of the current density. The magnetic fluctuations in the RFP are due to resistive MHD instabilities caused by current profile peaking; thus confinement in the RFP is ultimately the result of a misalignment between inductively driven current profiles and the stable current profiles characteristic of the Taylor state. If a technique such as rf current drive can be developed to non-inductively sustain a Taylor state (a current profile linearly stable to all tearing modes), the confinement of the RFP and its potential as a reactor concept are likely to increase. Whether there is a self-consistent path from poor confinement to greatly improved confinement through current profile modification is an issue for future experiments to address if and only if near term experiments can demonstrate: (1) coupling to and the propagation of rf waves in RFP plasmas, (2) efficient current drive, and (3) control of the power deposition which will make it possible to control the current profile. In this paper, modeling results and experimental plans are presented for two rf experiments which have the potential of satisfying these three goals: high-n{sub {parallel}} lower hybrid (LH) waves and electron Bernstein waves (EBWs).
Date: April 1, 1999
Creator: Forest, C.B.; Chattopadhyay, P.K.; Nornberg, M.D.; Prager, S.C.; Thomas, M.A.; Uchimoto, E. et al.
Partner: UNT Libraries Government Documents Department

Electron thermal transport in enhanced core confinement regimes

Description: The cause of the anomalous electron thermal transport in a region of suppressed ion thermal transport is investigated using a comprehensive gyrokinetic stability code. Analysis of a DIII-D negative central shear discharge with additional fastwave electron heating is presented. It is found that the electron heating excites the electron temperature gradient mode (ETG). The enhanced electron thermal transport from power balance analysis is consistent with the increased growth rate for the ETG mode. The ion thermal transport barrier is observed to retreat towards the plasma center during the fastwave heating (FW). Transport modeling with self-consistent E x B velocity shear reproduces this effect for on-axis electron heating. The same transport model predicts that off-axis electron heating can extend the region of reduced transport outward.
Date: July 1998
Creator: Staebler, G. M.; Waltz, R. E. & Greenfield, C. M.
Partner: UNT Libraries Government Documents Department