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Experience with Zr-Al getter pumps in the ISX-B tokamak

Description: Zr-Al getter pumps have been used in the ISX-B tokamak in connection with a series of pump limiter experiments. Experience with these pumps in this environment has revealed several problems that may limit their usefulness under typical tokamak operating conditions. Although the pumps perform satisfactorily while in operation with hydrogenic pumping speeds of 1-2 x 10/sup 3/ L/s at pressures of approx. 10 mtorr, some unknown mechanism, on occasion, slightly activates pumps that had been previously passive. Such behavior precludes the use of any operations that require high hydrogen pressures in the torus. Additionally, discharge cleaning operations cannot be safely carried out after the pumps are fully activated. Continued use of the pumps eventually leads to destruction of two getter cartridges from hydrogen embrittlement.
Date: January 1, 1983
Creator: Emerson, L.C.; Mioduszewski, P.K. & Simpkins, J.E.
Partner: UNT Libraries Government Documents Department

Design of the ISX-B differentially pumped bellows

Description: The structural design and operational aspects of the ISX-B differentially pumped bellows assembly are discussed. The ISX-B vacuum vessel consists of two monolithic halves which are rectangular in cross section and joined together by short bellows which provide electrical resistance around the vesel in the toroidal direction. The bellows are unable to withstand atmospheric pressure and must be mounted within an outer, thick-wall vessel with the space between bellows and wall being pumped down to a partial vacuum.
Date: January 1, 1977
Creator: Goranson, P.L.
Partner: UNT Libraries Government Documents Department

0. 4 mm interferometer system using dielectric waveguide

Description: A 0.4 mm submillimeter-wave, phase-modulated polarimeter/interferometer is used for simultaneous time-dependent measurement of line-averaged electron density and poloidal field-induced Faraday rotation along chords of the plasma column in ISX-B tokamak. Heterodyna detection and hollow dielectric waveguide are utilized to achieve the high sensitivity required for the multichord equipment.
Date: January 1, 1982
Creator: Hutchinson, D. P.; Ma, C. H.; Staats, P. A. & Vander Sluis, K. L.
Partner: UNT Libraries Government Documents Department

High beta results in ISX-B with intense neutral beam injection

Description: Experiments on the ISX-B device show a deterioration in confinement at high beam power. In particular the electron energy confinement time falls catastrophically with increasing beam power. The maximum volume averaged beta values achieved are <2.5%; this is much less than would be predicted by extrapolating the low power data. Elongation has not been observed to have any significant effect on the maximum attainable beta, perhaps due to the limited range of both internal and external elongation. The electron energy confinement time does not follow Alcator scaling at high injection powers. There are two likely candidates for the loss of confinement. The phenomena may be ..beta../sub p/ specific and caused by the gradual onset of resistive MHD pressure driven modes producing deteriorating confinement through fluctuations in the poloidal magnetic field. Alternatively the phenomena may be specific to the method of heating, neutral injection, being caused, for example, by plasma rotation, where the rotation speed approaches the ion thermal velocity. Experiments are in progress to investigate both of these possibilities.
Date: January 1, 1982
Creator: Edmonds, P.H.; Bates, S.C. & Bell, J.D.
Partner: UNT Libraries Government Documents Department

Gettering in ISX-B

Description: Gettering is used in the ISX-B tokamak to reduce the impurity concentration. This paper documents the gettering process used, and compares the expected changes in recycling and radiation with those observed experimentally. The enlargement of the operating regime (1/q, anti n/sub e/ R/B/sub phi/ space) is discussed. Finally, the effect on one of the objectives of the experimental program, that of obtaining high values of beta, is described.
Date: January 1, 1982
Creator: Wootton, A.J.; Edmonds, P.H.; Isler, R.C. & Mioduszewski, P.
Partner: UNT Libraries Government Documents Department

ISX-A graphite limiter experiment

Description: Graphite limiters were installed and tested in the ISX-A tokamak as part of the ISX-A surface physics program and the TFTR materials research program. The puropse of the experiment was to compare plasma performance using graphite limiters as opposed to the standard ISX-A stainless steel limiters. Heaters were installed in the graphite limiters so that the effects of operation at elevated temperatures could be evaluated.
Date: January 1, 1979
Creator: Langley, R.A.; Colchin, R.J.; Isler, R.C.; Murakami, M.; Simpkins, J.E.; Cecchi, J.L. et al.
Partner: UNT Libraries Government Documents Department

ISX objectives and physics

Description: The ISX-B program has achieved average beta values of 1.8% in a relatively clean plasma with neutral beam injection power greater than 10 times ohmic power input. Total beta has increased smoothly with beam power so far and exceeded theoretical limits with no indication that ballooning or any other instability is significantly increasing the energy loss rate.
Date: January 1, 1979
Creator: Mihalczo, J.T.
Partner: UNT Libraries Government Documents Department

MHD activity in the ISX-B tokamak: experimental results and theoretical interpretation

Description: The observed spectrum of MHD fluctuations in the ISX-B tokamak is clearly dominated by the n=1 mode when the q=1 surface is in the plasma. This fact agrees well with theoretical predictions based on 3-D resistive MHD calculations. They show that the (m=1; n=1) mode is then the dominant instability. It drives other n=1 modes through toroidal coupling and n>1 modes through nonlinear couplings. These theoretically predicted mode structures have been compared in detail with the experimentally measured wave forms (using arrays of soft x-ray detectors). The agreement is excellent. More detailed comparisons between theory and experiment have required careful reconstructions of the ISX-B equilibria. The equilibria so constructed have permitted a precise evaluation of the ideal MHD stability properties of ISX-B. The present results indicate that the high ..beta.. ISX-B equilibria are marginally stable to finite eta ideal MHD modes. The resistive MHD calculations also show that at finite ..beta.. there are unstable resistive pressure driven modes.
Date: January 1, 1982
Creator: Carreras, B.A.; Dunlap, J.L.; Bell, J.D.; Charlton, L.A.; Cooper, W.A.; Dory, R.A. et al.
Partner: UNT Libraries Government Documents Department

Determination of the global recombination rate coefficient for the ISX-B Tokamak

Description: The global recombination rate coefficient for hydrogen has been measured for the ISX-B tokamak vacuum vessel for various surface conditions. The measurements were performed by observing the rate of decrease of gas pressure in the vessel during a glow discharge. The parameters of the glow discharge and the complete experimental method are described. Previously published analytic and numerical models are used for data analysis. The effects of surface contamination on the results are described. For ''unclean'' wall conditions sigmak/sub r/ = 1.8 x 10/sup -28/ cm/sup 4//atom.s at 296 K and increases to sigmak/sub r/ = 4.4 x 10/sup -28/ cm/sup 4//atoms.s for ''clean'' conditions and remains constant until subsequent exposure to air.
Date: January 1, 1983
Creator: Langley, R.A. & Howe, H.C.
Partner: UNT Libraries Government Documents Department

Determination of plasma shape from poloidal field measurements on ISX-B

Description: The ISX-B tokamak has a poloidal coil system designed to produce circular, elliptical, and D-shaped plasmas. Plasma shape and low-order multipole moments of the plasma current distribution are determined from experimental measurements of B/sub Z/, B/sub R/, and/or psi around the periphery of the vacuum chamber. The experimental arrangement and method of analysis of results, using a least squares method to fit the data points to a finite current filament model, are described in this report. Plasma shape results for circular and D-shaped plasmas with b/a less than or equal to 1.5 and an analysis of the sensitivity of the technique to measurement errors are presented. The results indicate that this method gives accurate measurements of the plasma boundary and is relatively insensitivie to errors.
Date: March 1, 1980
Creator: Swain, D.W.; Bates, S.; Neilson, G.H. & Peng, Y.K.M.
Partner: UNT Libraries Government Documents Department

Assembly of ISX

Description: The Impurity Study Experiment, a moderate size tokamak, was recently assembled at ORNL. Demountable toroidal field coils allowed for the assembly of major components at remote locations and rapid installation into ISX. A discharge cleaning plasma was generated in ISX six weeks after the arrival of the final toroidal field coil. A chronological summary of the assembly is presented, emphasizing features designed to aid in assembly and maintenance. A cross-section of the machine showing the major mechanical components to be discussed is given.
Date: January 1, 1977
Creator: Durfee, N.W.
Partner: UNT Libraries Government Documents Department

Design and fabrication of the impurity study experiment (ISX) coils

Description: ISX, an Impurity Study Experiment, is a moderately sized tokamak that has recently begun operation at Oak Ridge National Laboratory. The details of the design and construction of the coil sets are emphasized. A very brief summary of the basic parameters is presented and an overall view of the tokamak is shown.
Date: January 1, 1977
Creator: Lousteau, D.C. & Hussung, R.O.
Partner: UNT Libraries Government Documents Department

Review of the beta situation

Description: This note lists some of the possible causes of beta limitation in tokamak and discusses what is known and what is involved in investigating them. The motivation for preparing this note is the observed degradation of confinement with increasing beta poloidal ..beta../sub p/ and beam power P/sub b/ in ISX-B.
Date: January 18, 1982
Creator: Sheffield, J.
Partner: UNT Libraries Government Documents Department

Impurity studies in fusion devices using laser-fluorescence-spectroscopy

Description: Resonance fluorescence excitation of neutral atoms using tunable radiation from dye lasers offers a number of unique advantages for impurity studies in fusion devices. Using this technique, it is possible to perform local, time-resolved measurements of the densities and velocity distributions of metallic impurities in fusion devices without disturbing the plasma. Velocities are measured by monitoring the fluorescence intensity while tuning narrow bandwidth laser radiation through the Doppler - broadened absorbtion spectrum of the transition. The knowledge of the velocity distribution of neutral impurities is particularly useful for the determination of impurity introduction mechanisms. The laser fluorescence technique will be described in terms of its application to metallic impurities in fusion devices and related laboratory experiments. Particular attention will be given to recent results from the ISX-B tokamak using pulsed dye lasers where detection sensitivities for neutral Fe of 10/sup 6/ atoms/cm/sup 3/ with a velocity resolution of 600 m/sec (0.1 eV) have been achieved. Techniques for exciting plasma particles (H,D) will also be discussed.
Date: August 1, 1980
Creator: Husinsky, W.R.
Partner: UNT Libraries Government Documents Department

Plasma position dynamics of ISX tokamak

Description: Perturbation equations of a tokamak plasma equilibrium position have been developed. Neglecting second and higher order effects, oscillatory high frequency solution is obtained, and an approximated low frequency plasma motion dynamics transfer function is derived. This function allows a manageable study of a tokamak plasma equilibrium position stability and practical syntheses of the associated plasma position feedback control systems. One of the major parameters governing plasma equilibrium position stability of a tokamak is shown to be the vacuum vessel eddy current delay time constant.
Date: January 1, 1977
Creator: Burenko, O.
Partner: UNT Libraries Government Documents Department

Submillimeter wave propagation in tokamak plasmas

Description: The propagation of submillimeter-waves (smm) in tokamak plasmas has been investigated both theoretically and experimentally to ensure successful measurements of electron density and plasma current distributions in tokamak devices. Theoretical analyses have been carried out to study the polarization of the smm waves in TFTR and ISX-B tokamaks. A multichord smm wave interferometer/polarimeter system has been employed to simultaneously measure the line electron density and poloidal field-induced Faraday rotation in the ISX-B tokamak. The experimental study on TFTR is under way. Computer codes have been developed and have been used to study the wave propagation and to reconstruct the distributions of plasma current and density from the measured data. The results are compared with other measurements.
Date: January 1, 1985
Creator: Ma, C.H.; Hutchinson, D.P.; Staats, P.A.; Vander Sluis, K.L.; Mansfield, D.K.; Park, H. et al.
Partner: UNT Libraries Government Documents Department

Particle removal with pump limiters in ISX-B

Description: First pump limiter experiments were performed on ISX-B. Two pump limiter modules were installed in the top and bottom of one toroidal sector of the tokamak. The modules consist of inertia cooled, TiC coated graphite heads and Zr-Al getter pumps each with a pumping speed of 1000 to 2000 l/s. The objective of the initial experiments was the demonstration of plasma particle control with pump limiters. The first set of experiments were performed in ohmic discharges (OH) in which the effect of the pump limiters on the plasma density was clearly demonstrated. In discharges characterized by: I/sub p/ = 110 kA, B/sub T/ = 15 kG, anti n/sub e/ = 1 - 5 x 10/sup 13/ cm/sup -3/ and t = 0.3 s the pressure rise in the pump limiters was typically 2 mTorr with the pumps off and 0.7 mTorr after activating the pumps. When the pumps were activated, the line-average plasma density decreased by up to a factor 2 at identical gas flow rates. The second set of measurements were performed in neutral beam heated discharges (NBI) with injected powers between 0.6 MW and 1.0 MW. Due to a cooling problem on one of the Zr-Al pumps the NBI experiments were carried out with one limiter only. The maximum pressure observed in NBI-discharges was 5 mTorr without activating the pumps, i.e., approximately twice as high as in OH-discharges. The exhaust efficiency, which is defined as the removed particle flux over the total particle flux in the scrape-off layer is estimated to be 5%.
Date: January 1, 1983
Creator: Mioduszewski, P.; Emerson, L.C.; Simpkins, J.E.; Wootton, A.J.; Bush, C.E.; Carnevali, A. et al.
Partner: UNT Libraries Government Documents Department

Program plan for electron cyclotron heating experiments on the ISX tokamak

Description: A program of ECH on the new Oak Ridge tokamak, ISX-B, beginning in 1978 is proposed. Experiments will attempt bulk heating, preionization, and current profile control. The first experiments will be a test of the principle with a single 200-kW, 28-GHz gyrotron. It is then proposed to add one additional tube in FY 1979 for high ..beta.. studies, and--assuming successful heating experiments--an additional eight tubes during FY 1979-80 for an ECH flux conserving tokamak experiment. Target date for completion of the first experiments on ISX-B with approx. 200 kW is December 1978 at an estimated cost of $0.9 M. The second tube can be added in FY 1979 at an estimated cost of between $0.4 and $0.7 M, and the experiments with two tubes can proceed starting in the summer of 1979. Additional power up to 2 MW can be added at an estimated total cost of $1.75 to $5.00/W. These cost ranges reflect current technical uncertainties which will be resolved in the early phase(s) of the program. This report presents a design description of the proposed experiments, gives results of some theoretical analyses to predict performance, and includes estimates of costs and schedules.
Date: October 1, 1977
Creator: England, A. C.; Loring, C. M.; Eldridge, O. C.; Namkung, W.; Howe, H. C.; Campen, G. L. et al.
Partner: UNT Libraries Government Documents Department

Electron cyclotron heating experiment on the ISX-B tokamak

Description: This paper describes apparatus that will be used to provide 200 kW of microwave heating at 28 GHz to the ISX-B tokamak. The program goals and a brief explanation of the principles of microwave heating in a plasma are included in the introduction, and the current status of the project is outlined in the conclusion.
Date: January 1, 1979
Creator: Campen, G.L.; England, A.C.; Loring, C.M. & Wright, W.L.
Partner: UNT Libraries Government Documents Department

Neutral injection experiments on the ISX-B tokamak

Description: The following topics are described: (1) review of confinement scaling in ISX-B with strong neutral injection in clean plasmas, (2) discussion of observed energy confinement improvement in slightly contaminated discharges (factor less than or equal to 2), and (3) preliminary evaluation of confinement with balanced neutral beam injection. (MOW)
Date: January 1, 1983
Creator: Scott, S.D.
Partner: UNT Libraries Government Documents Department

Ray tracing package through a lens system and a spectrometer

Description: To study the light collection optics of the ISX-B two-dimensional (2-D) Thomson scattering system, we have implemented in the Oak Ridge National Laboratory (ORNL) Fusion Energy Division (FED) PDP-10 two computer programs, LENS and SPECT, that trace rays through a lens system and a spectrometer, respectively. The lens package follows the path of any kind of ray (meridional or skew) through a centered optical system formed by an arbitrary number of spherical surfaces. The spectrometer package performs geometrical ray tracing through a Czerney-Turner spectrometer and can be easily modified for studying any other configuration. Contained herein is a description of the procedures followed and a listing of the computer programs.
Date: March 1, 1980
Creator: Zurro, B.; King, P.W. & Lazarus, E.A.
Partner: UNT Libraries Government Documents Department

Structural design and analysis for the ISX-C/ATF tokamak of the vacuum vessel, coil joints, and supports

Description: The ISX-C/ATF is being designed as a test bed for advanced toroidal concepts. Because of numerous design concepts being evaluated, a flexible, easily changeable structural-design math-model was needed to afford quick evalution of the structural feasibility of the many proposed concepts. To satisfy this need, the NASTRAN Automated Multi-Stage Substructures technique was used to build a quick-changeable math model. This technique was especially needed because all the coils, first wall and diagnostic devices are to be supported by the vacuum vessel, requiring the entire structure to be analyzed as a system. Without the use of the substructuring technique, the required man hours and computer core would have made timely design analysis impossible. To illustrate the technique, the detailed design analysis of the concept Torsatron (with helical coils and T.F. coils) is presented.
Date: January 1, 1981
Creator: Mayhall, J.A.; Cain, W.D.; Hammonds, C.J.; Johnson, R.L. & Gray, W.H.
Partner: UNT Libraries Government Documents Department