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Study of the mass and energy resolution of the E parallel B charge exchange analyzer for TFTR

Description: The charge exchange diagnostic for TFTR requires simultaneous multispecie (H/sup +/, D/sup +/, ..gamma../sup +/) analysis of particles in the energy range of 0.5 - 150 keV. The analyzer design chosen to provide this capability employs a wide gap semi-circular region of superimposed parallel electric and magnetic fields to accomplish mass and energy resolution, respectively. Combined with a large area, multi-anode microchannel plate detector, this arrangement will enable the energy distributions of protons, deuterions, and tritons to be measured concurrently as a function of time during each discharge. A computer simulation program for calculating ion trajectories through the analyzer was written that includes a realistic model of the magnetic and electrostatic fringe fields. This report presents the results of a study of the proposed E parallel B analyzer, and it reveals that the fringe fields are not detrimental to the performance of the analyzer.
Date: September 1, 1979
Creator: Kaita, R. & Medley, S.S.
Partner: UNT Libraries Government Documents Department

Improvement in Plasma Performance with Lithium Coatings in NSTX

Description: Lithium as a plasma-facing material has attractive features, including a reduction in the recycling of hydrogenic species and the potential for withstanding high heat and neutron fluxes in fusion reactors. Dramatic effects on plasma performance with lithium-coated plasma-facing components (PFC's) have been demonstrated on many fusion devices, including TFTR, T-11M, and FT-U. Using a liquid-lithium-filled tray as a limiter, the CDX-U device achieved very significant enhancement in the confinement time of ohmically heated plasmas. The recent NSTX experiments reported here have demonstrated, for the first time, significant and recurring benefits of lithium PFC coatings on divertor plasma performance in both L- and H- mode regimes heated by neutral beams.
Date: February 17, 2009
Creator: Kaita, R
Partner: UNT Libraries Government Documents Department

Fast time resolution charge-exchange measurements during the fishbone instability in the poloidal divertor experiment

Description: Measurements of fast ion losses due to the fishbone instability during high ..beta../sub T/q neutral beam heated discharges in the Poloidal Divertor Experiment have been made using two new vertical-viewing charge-exchange analyzers. The measurements show that the instability has an n=1 toroidal mode number, and that it ejects beam ions in a toroidally rotating beacon directed outward along a major radius. Observations of ejected ions with energies up to twice the beam injection energy at R approx. = R/sub 0/ + a indicate the presence of a non-..mu..-conserving acceleration mechanism.
Date: January 1, 1984
Creator: Beiersdorfer, P.; Kaita, R. & Goldston, R.J.
Partner: UNT Libraries Government Documents Department

Characteristics of solid-target charge-exchange analyzers for energetic ion diagnostics on tokamaks

Description: Compact electrostatic charge-exchange analyzers have been constructed for installation in areas of high magnetic fields and restricted access near tokamak fusion devices. The analyzers employed carbon stripping foils, and have been calibrated for proton energies between 1 and 70 keV. They have been successfully used to study charge-exchange losses in auxiliary-heated tokamak plasmas.
Date: May 1, 1987
Creator: Beiersdorfer, P.; Roquemore, A.L. & Kaita, R.
Partner: UNT Libraries Government Documents Department

Plasma Performance Improvement with Lithium-Coated Plasma-Facing Components in NSTX

Description: Lithium as a plasma-facing material has many attractive features, including a reduction in the recycling of hydrogenic species and the potential for withstanding high heat and neutron fluxes in fusion reactors. Recent NSTX experiments have shown, for the first time, significant and recurring benefits of lithium coatings on plasma-facing components (PFC's) to the performance of divertor plasmas in both L- and H- mode confinement regimes heated by high-power neutral beams. They included decreases in the plasma density and inductive flux consumption, and increases in the electron temperature, ion temperature, energy confinement time, and DD neutron rate. Extended periods of MHD quiescence were also achieved, and measurements of the visible emission from the lower divertor showed a reduction in the deuterium, carbon, and oxygen line emission. Other salient results with lithium evaporation included a broadening of the electron temperature profile, and changes in edge density gradients that benefited electron Bernstein wave coupling. There was also a reduction in ELM frequency and amplitude, followed by a period of complete ELM suppression. In general, it was observed that both the best and the average confinement occurred after lithium deposition and that the increase in WMHD occurs mostly through an increase in We. In addition, a liquid lithium divertor (LLD) is being installed on NSTX this year. As the first fully-toroidal liquid metal divertor target, experiments with the LLD can provide insight into the behavior of metallic ITER PFC's should they liquefy during high-power divertor tokamak operations. The NSTX lithium coating and LLD experiments are important near-term steps in demonstrating the potential of liquid lithium as a solution to the first-wall problem for both magnetic and inertial fusion reactors.
Date: September 29, 2008
Creator: Kaita, R., et. al.
Partner: UNT Libraries Government Documents Department

Measurements of energetic helium-3 minority distributions during ion cyclotron radio-frequency heating in the Princeton Large Torus

Description: Ion cyclotron radio-frequency heating experiments were performed with a /sup 3/He minority ion species in a /sup 4/He majority plasma in the Princeton Large Torus. The energetic /sup 3/He ion ''tail'' was measured directly with a charge exchange neutral analyzer for the first time. Comparisons with bounce-averaged quasi-linear calculations suggest a modestly peaked radi-frequency power deposition profile. The double charge exchange process /sup 3/He/sup + +/ )plus) /sup 4/He/sup 0/ )plus) /sup 3/He/sup 0/ )plus) /sup 4/He/sup + +/ demonstrated in these measurements may be useful as part of an alpha particle diagnostic in a fusion reactor experiment. 18 refs., 4 figs.
Date: March 1, 1988
Creator: Hammett, G.W.; Kaita, R. & Wilson, J.R.
Partner: UNT Libraries Government Documents Department

Monte Carlo simulation of ion trajectories in the modified PDX thermal charge exchange analyzer

Description: An improved design for the present PDX thermal charge exchange analyzer (MACE) has been proposed by one of the authors, in which the five cylindrical electrostatic plates for mass separation are replaced by a single flat, electrostatic deflection plate. An existihg Monte Carlo code that simulated the passage of ions through the MACE analyzer was modified to examine the feasibility of this change. The resulting calculations were used to optimize detector positions and collimation requirements. The first analyzer to be placed on PDX will be of the old design, similar to the present PLT analyzer. However, if the design reported here is successful on the test stand, the future PDX analyzers will all be of the new, single electrostatic plate variety. A further advantage will be the ability to install as many as ten detectors instead of the current five, thus providing twice as many energy channels for each shot. Also, both mass species (H, D) can be measured concurrently, if desired.
Date: December 1, 1978
Creator: Kaita, R.; Davis, S.L. & Medley, S.S.
Partner: UNT Libraries Government Documents Department

Observation of neoclassical effects on neutral beam injected ions in PLT

Description: The horizontally-scanning charge exchange analyzer on the Princeton Large Torus (PLT) was used to measure fast co-moving ions during counter-injection of neutral beams. The large flux of charge exchange neutrals observed under these circumstances exhibited a sharp cutoff as the analyzer was moved toward more parallel radii of tangency. At a fixed angle and beam energy, the cutoff showed a strong dependence on the plasma current. Monte-Carlo calculations using a Fokker-Planck formalism and full toroidal geometry give substantive agreement with the experimental data, indicating that neoclassical effects on neutral beam injected ions were directly observed.
Date: January 1, 1981
Creator: Kaita, R.; Goldston, R.J. & Bussac, J.P.
Partner: UNT Libraries Government Documents Department

Neutral beam species measurements using in situ Rutherford backscatter spectrometry

Description: This work describes a new in situ method for measuring the neutral particle fractions in high power deuterium neutral beams, used to heat magnetically confined fusion plasmas. Deuterium beams, of variable energies, pulse lengths, and powers up to 47 keV, 100 msec, 1.6 MW, were Rutherford backscattered at 135/sup 0/ from TiC inner neutral beam armor of the PDX, and detected using an electrostatic analyzer with microchannel plates. Complete energy scans were made every 20 msec and data were obtained simultaneously from five different positions across the beam profile. The neutral particle fractions were measured to be D/sup 0/(E):D/sup 0/(E/2):D/sup 0/(E/3)=53:32:15. The corresponding neutral power fractions were P/sup 0/(E):P/sup 0/(E/2):P/sup 0/(E/3)=72:21:7, and the associated ionic fractions at the output of the ion source were D/sub 1//sup +/(E):D/sub 2//sup +/(E):D/sub 3//sup +/(E)=74:20:6. The measured neutral particle fractions were relatively constant over more than 70% of the beam power distribution. A decrease in the yield of the full energy component in the outer regions of the beam was observed. Other possible experimental configurations and geometries are discussed.
Date: December 1, 1984
Creator: Kugel, H.W.; Kaita, R.; Gammel, G. & Williams, M.D.
Partner: UNT Libraries Government Documents Department

High time resolution ion temperature profile measurements on PBX

Description: Ion temperature profiles with a time resolution of 2 to 5 ms have been measured on PBX by charge-exchange-recombination spectroscopy (CXRS) and a neutral-particle charge-exchange analyzer (NPA). The sightlines of both diagnostics crossed the trajectory of a near-perpendicular heating beam, which enhanced the local neutral density (proportional to signal strength) and provided spatial resolution. The time resolution of these two independent techniques is sufficient to see sawtooth oscillations and other MHD activity. Effects of these phenomena on the toroidal rotation velocity profile, v/sub phi/(r), are clearly observed by CXRS. For example, a sharp drop in the central v/sub phi/ occurs at the sawtooth crash, followed by a linear rise during the quiescent phase. The NPA results are compared with those from CXRS.
Date: May 1, 1986
Creator: Gammel, G.; Kaita, R.; Fonck, R.; Jaehnig, K. & Powell, E.
Partner: UNT Libraries Government Documents Department

Electron Density Measurements in the National Spherical Torus Experiment Detached Divertor Region Using Stark Broadening of Deuterium Infrared Paschen Emission Lines

Description: Spatially resolved measurements of deuterium Balmer and Paschen line emission have been performed in the divertor region of the National Spherical Torus Experiment using a commercial 0.5 m Czerny-Turner spectrometer. While the Balmer emission lines, Balmer and Paschen continua in the ultraviolet and visible regions have been extensively used for tokamak divertor plasma temperature and density measurements, the diagnostic potential of infrared Paschen lines has been largely overlooked. We analyze Stark broadening of the lines corresponding to 2-n and 3-m transitions with principle quantum numbers n = 7-12 and m = 10-12 using recent Model Microfield Method calculations (C. Stehle and R. Hutcheon, Astron. Astrophys. Supl. Ser. 140, 93 (1999)). Densities in the range (5-50) x 10{sup 19} m{sup -3} are obtained in the recombining inner divertor plasma in 2-6 MW NBI H-mode discharges. The measured Paschen line profiles show good sensitivity to Stark effects, and low sensitivity to instrumental and Doppler broadening. The lines are situated in the near-infrared wavelength domain, where optical signal extraction schemes for harsh nuclear environments are practically realizable, and where a recombining divertor plasma is optically thin. These properties make them an attractive recombining divertor density diagnostic for a burning plasma experiment.
Date: April 27, 2007
Creator: Soukhanovskii, V A; Johnson, D W; Kaita, R & Roquemore, A L
Partner: UNT Libraries Government Documents Department

The Impact Of Lithium Wall Coatings On NSTX Discharges And The Engineering Of The Lithium Tokamak eXperiment (LTX)

Description: Recent experiments on the National Spherical Torus eXperiment (NSTX) have shown the benefits of solid lithium coatings on carbon PFC's to diverted plasma performance, in both Land H- mode confinement regimes. Better particle control, with decreased inductive flux consumption, and increased electron temperature, ion temperature, energy confinement time, and DD neutron rate were observed. Successive increases in lithium coverage resulted in the complete suppression of ELM activity in H-mode discharges. A liquid lithium divertor (LLD), which will employ the porous molybdenum surface developed for the LTX shell, is being installed on NSTX for the 2010 run period, and will provide comparisons between liquid walls in the Lithium Tokamak eXperiment (LTX) and liquid divertor targets in NSTX. LTX, which recently began operations at the Princeton Plasma Physics Laboratory, is the world's first confinement experiment with full liquid metal plasma-facing components (PFCs). All materials and construction techniques in LTX are compatible with liquid lithium. LTX employs an inner, heated, stainless steel-faced liner or shell, which will be lithium-coated. In order to ensure that lithium adheres to the shell, it is designed to operate at up to 500 - 600 oC to promote wetting of the stainless by the lithium, providing the first hot wall in a tokamak to operate at reactor-relevant temperatures. The engineering of LTX will be discussed.
Date: March 18, 2010
Creator: Majeski, R.; Kugel, H. & Kaita, R.
Partner: UNT Libraries Government Documents Department

Spreading of wave-driven currents in a tokamak

Description: Lower hybrid current drive (LHCD) in the tokamak Princeton Beta Experiment-Modification (PBX-M) is computed with a dynamic model in order to understand an actual discharge aimed at raising the central q above unity. Such configurations offer advantages for steady-state operation and plasma stability. For the particular parameters of this PBX-M experiment, the calculation found singular profiles of plasma current density J and safety factor q developing soon after LHCD begins. Smoothing the lower hybrid-driven current and power using a diffusion-Eke equation and a velocity-independent diffusivity for fast-electron current brought the model into reasonable agreement with the measurements if D{sub fast} {approx} 1.0 m{sup 2}/s. Such a value for D{sub fast} is in the range suggested by other work.
Date: January 1996
Creator: Ignat, D. W.; Kaita, R.; Jardin, S. C. & Okabayashi, M.
Partner: UNT Libraries Government Documents Department

Current profile modification during lower hybrid current drive in the Princeton Beta Experiment-Modification

Description: Current profile modification with lower hybrid waves has been demonstrated in the Princeton Beta Experiment-Modification tokamak. When the n{parallel} spectrum of the launched waves was varied, local changes in the current profile were observed according to equilibria reconstructed from motional Stark effect polarimetry measurements. Changes in the central safety factor (q) were also determined to be a function of the applied radio frequency (rf) power. These results have been modeled with the Tokamak Simulation Code/Lower Hybrid Simulation Code, which is able to duplicate the general trends seen in the data.
Date: February 1, 1996
Creator: Kaita, R.; Bell, R. & Batha, S.H.
Partner: UNT Libraries Government Documents Department

Rogowski Loop design for NSTX

Description: The Rogowski Loop is one of the most basic diagnostics for tokamak operations. On the National Spherical Torus Experiment (NSTX), the plasma current Rogowski Loop had the constraints of the very limited space available on the center stack, 5,000 volt isolation, flexibility requirements as it remained a part of the Center Stack assembly after the first phase of operation, and a +120 C temperature requirement. For the second phase of operation, four Halo Current Rogowski Loops under the Center Stack tiles will be installed having +600 C and limited space requirements. Also as part of the second operational phase, up to ten Rogowski Loops will installed to measure eddy currents in the Passive Plate support structures with +350 C, restricted space, and flexibility requirements. This presentation will provide the details of the material selection, fabrication techniques, testing, and installation results of the Rogowski Loops that were fabricated for the high temperature operational and bakeout requirements, high voltage isolation requirements, and the space and flexibility requirements imposed upon the Rogowski Loops. In the future operational phases of NSTX, additional Rogowski Loops could be anticipated that will measure toroidal plasma currents in the vacuum vessel and in the Passive Plate assemblies.
Date: January 6, 2000
Creator: McCormack, B.; Kaita, R.; Kugel, H. & Hatcher, R.
Partner: UNT Libraries Government Documents Department

Diagnostic Development on NSTX

Description: Diagnostics are described which are currently installed or under active development for the newly commissioned NSTX device. The low aspect ratio (R/a less than or equal to 1.3) and low toroidal field (0.1-0.3T) used in this device dictate adaptations in many standard diagnostic techniques. Technical summaries of each diagnostic are given, and adaptations, where significant, are highlighted.
Date: December 16, 1999
Creator: Roquemore, A.L.; Johnson, D.; Kaita, R. & al, et
Partner: UNT Libraries Government Documents Department

Plasma ion temperature measurements via charge-exchange recombination radiation

Description: Spatially and temporally resolved plasma ion temperatures can be determined by measuring the Doppler-broadened line profiles of transitions excited by charge-exchange recombination reactions between fast hydrogen atoms and fully ionized low-Z ions. Plasma rotation velocity profiles can also be obtained. A sample result from the PDX tokamak using He/sup +/ radiation is presented, and expected line intensities for model cases for PDX and TFTR are calculated.
Date: November 1, 1982
Creator: Fonck, R.J.; Goldston, R.J.; Kaita, R. & Post, D.E.
Partner: UNT Libraries Government Documents Department

Neutral Probe Beam q-profile measurements in PDX and PBX-M

Description: Using the Fast Ion Diagnostic Experiment (FIDE) technique, a Neutral Probe Beam (NPB) can be aimed to inject tangentially to a magnetic surface. The resultant ion orbit shifts, due to conservation of canonical toroidal angular momentum, can be measured with a multi-sightline charge-exchange analyzer to yield direct measurements of radial magnetic flux profiles, current density profiles, the radial position of the magnetic axis, flux surface inner and outer edges, q-profiles, and central-q time dependencies. An extensive error analysis was performed on previous PDX q-measurements in circular plasmas and the resulting estimated contributions of various systematic effects are discussed. Preliminary results of fast ion orbit shift measurements at early times in indented PBX-M plasmas are given. Methods for increasing the absolute experimental precision of similar measurements in progress on PBX-M are discussed. 4 refs., 3 figs.
Date: June 1, 1988
Creator: Kugel, H.W.; Gammel, G.M.; Kaita, R.; Reusch, M.F. & Roberts, D.W.
Partner: UNT Libraries Government Documents Department

Ion temperature by charge exchange neutral analysis from vertical sightlines on the Tokamak Fusion Test Reactor

Description: The Fokker-Planck code FPPRF is used to calculate the expected deuterium charge exchange flux along vertical sighlines from TFTR neutral-beam-injected discharges. The feasibility of obtaining central ion temperature measurements by fitting the spectra obtained from these sightlines at two energy regions--above the highest neutral beam injection energy (> 100 keV) and from 20-80 keV--is investigated. It is demonstrated that the central ion temperature can be obtained from the central vertical slightline for fitting the high energy data. The deuterium neutral particle flux energy distribution below the neutral beam injection energy is insentive to the code input ion temperature, however. 6 refs., 12 figs., 1 tab.
Date: December 1, 1987
Creator: Fiore, C.L.; Medley, S.S.; Hammett, G.W.; Kaita, R. & Scott, S.D.
Partner: UNT Libraries Government Documents Department

Measurements of beam-ion confinement during tangential beam-driven instabilities in PBX (Princeton Beta Experiment)

Description: During tangential injection of neutral beams into low density tokamak plasmas with ..beta.. > 1% in the Princeton Beta Experiment (PBX), instabilities are observed that degrade the confinement of beam ions. Neutron, charge-exchange, and diamagnetic loop measurements are examined in order to identify the mechanism or mechanisms responsible for the beam-ion transport. The data suggest a resonant interaction between the instabilities and the parallel energetic beam ions. Evidence for some nonresonant transport also exists.
Date: January 1, 1987
Creator: Heidbrink, W.W.; Kaita, R.; Takahashi, H.; Gammel, G.; Hammett, G.W. & Kaye, S.
Partner: UNT Libraries Government Documents Department

Magnetic Diagnostics for Equilibrium Reconstructions in the Presence of Nonaxisymmetric Eddy Current Distributions in Tokamaks

Description: The lithium tokamak experiment #2;LTX#3; is a modest-sized spherical tokamak #2;R0=0.4 m and a =0.26 m#3; designed to investigate the low-recycling lithium wall operating regime for magnetically confined plasmas. LTX will reach this regime through a lithium-coated shell internal to the vacuum vessel, conformal to the plasma last-closed-flux surface, and heated to 300-400 oC. This structure is highly conductive and not axisymmetric. The three-dimensional nature of the shell causes the eddy currents and magnetic fields to be three-dimensional as well. In order to analyze the plasma equilibrium in the presence of three-dimensional eddy currents, an extensive array of unique magnetic diagnostics has been implemented. Sensors are designed to survive high temperatures and incidental contact with lithium and provide data on toroidal asymmetries as well as full coverage of the poloidal cross-section. The magnetic array has been utilized to determine the effects of nonaxisymmetric eddy currents and to model the start-up phase of LTX. Measurements from the magnetic array, coupled with two-dimensional field component modeling, have allowed a suitable field null and initial plasma current to be produced. For full magnetic reconstructions, a three-dimensional electromagnetic model of the vacuum vessel and shell is under development.
Date: December 10, 2010
Creator: Kaita, R.; Kozub, T.; Logan, N.; Majeski, R.; Menard, J. & Zakharov, L.
Partner: UNT Libraries Government Documents Department

Measuring the Density of a Molecular Cluster Injector via Visible Emission from an Electron Beam

Description: A method to measure the density distribution of a dense hydrogen gas jet is pre- sented. A Mach 5.5 nozzle is cooled to 80K to form a flow capable of molecular cluster formation. A 250V, 10mA electron beam collides with the jet and produces Hα emission that is viewed by a fast camera. The high density of the jet, several 10<sup>16</sup>cm<sup>-3</sup>, results in substantial electron depletion, which attenuates the H<sub>α</sub> emission. The attenuated emission measurement, combined with a simplified electron-molecule collision model, allows us to determine the molecular density profile via a simple iterative calculation.
Date: June 28, 2010
Creator: Lundberg, D. P.; Kaita, R.; Majeski, R. M. & Stotler, D. P.
Partner: UNT Libraries Government Documents Department