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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

Performance of Zr-Al getter pumps under transient load conditions

Description: Testing of the pump limiter concept in the Impurity Study Experiment (ISX-B) tokamak will involve the use of Zr-Al nonevaporable getter pumps capable of handling intermittent pulses of hydrogen and/or deuterium in the presence of carbon and oxygen impurity concentrations of several percent. To study the pumping characteristics under these conditions we have installed a Zr-Al cartridge pump in a vacuum chamber equipped with a fast gas puff feed system, a quadrupole residual gas analyzer, and a high speed ion gauge for transient pressure measurements. In this paper we report on the performance of the pump over a wide range of gas loads up to that sufficient to provide tens of monolayers coverage of the getter surface. With flow rates up to 13 torr L/s, pumping speeds for hydrogen were measured to be 1200-1500 L/s at pressures up to 10 mtorr. The measurements were carried out with gas pulses ranging in length from 50 ms to over 1 s and under conditions that provided a constant pumping speed for impurity species.
Date: January 1, 1983
Creator: Emerson, L.C.; Mioduszewski, P.K. & Simpkins, J.E.
Partner: UNT Libraries Government Documents Department

Weight change measurements of erosion/deposition at beryllium limiter tiles in ISX-B

Description: The weight changes of Be tiles which functioned as a rail limiter in ISX-B for more than 3500 beam-heated discharges have been determined. The net weight loss for the limiter was 2.0 g, with the central tiles losing a total of 3.2 g and inboard tiles gaining 1.2 g. The weight loss is attributed primarily to the release of Be droplets as a result of limiter surface melting. The weight gains resulted from an inward flow of molten material along the limiter surface. The results indicate high erosion (melt loss) with incomplete and nonuniform redeposition (melt flow) of limiter material during periods of limiter melting.
Date: July 1, 1985
Creator: Roberto, J.B.; Edmonds, P.H.; England, A.C.; Gabbard, A. & Zuhr, R.A.
Partner: UNT Libraries Government Documents Department

Pumped limiter development on ISX

Description: Pumped limiter configurations are being suggested for FED and INTOR for helium ash exhaust and fuel particle control. The goal of the pump limiter studies in ISX is the selection of the most promising concept and its evaluation in the ISX-C device under the following conditions: (1) quasi steady state operation (less than or equal to 30s), (2) high edge power densities, and (3) particle control by means of mechanical devices. We are considering various options, including particle scraper and ballistic particle collection concepts as well as the current FED design. In ISX-B we will test a full-size pump limiter and directly compare the heat removal and particle control capabilities with a bundle divertor. In ISX-C the steady state operation characteristics of pump limiters will be explored.
Date: January 1, 1981
Creator: Mioduszewski, P.K.; Edmonds, P.H. & Sheffield, J.
Partner: UNT Libraries Government Documents Department

Neutral beam data systems at ORNL

Description: A control system for neutral injection beam lines has been designed, implemented, and used with much success. Despite the problems with very high power levels this system is very successful in relieving the operators burdens of slow conditioning, data recording, and mode switching. The use of computer control with multiple beam lines now appears very promising.
Date: January 1, 1982
Creator: Stewart, C.R.
Partner: UNT Libraries Government Documents Department

Observations of arcing in the ISX tokamak

Description: Arcing has been proposed as a major source of metal impurities in tokamak plasmas. Arc tracks have been observed in the ISX tokamak on the limiter, the inner-wall surface, and on the samples from the surface analysis station. Linear as well as fern-like arc tracks have been observed. From optical and SEM analysis of the tracks, it was estimated that about 10/sup 16/ to 10/sup 17/ atoms were released per arc. To study the influence of arcing on the tokamak discharge, an experiment was set up to measure electrical and optical signals of arcing in situ. In well controlled tokamak discharges, arcing was observed only during the initial breakdown of the plasma and during the quenching phase at the end of the discharge. In disrupted discharges, each plasma disruption was accompanied by arcing. The pulse-length of one single unipolar arc was measured to be about 50 ..mu..s and the current amplitude was typically about 20 A.
Date: January 1, 1979
Creator: Mioduszewski, P.; Clausing, R.E. & Heatherly, L.
Partner: UNT Libraries Government Documents Department

High-speed photographic observation of plasma-limiter interactions in ISX-B

Description: High-speed motion pictures confirm that arcing occurs during periods of plasma instability in ISX-B. Various types of plasma-limiter interactions are described and illustrated. Arcing and other visible phenomena are correlated to plasma parameters.
Date: January 1, 1981
Creator: Clausing, R.E.; Emerson, L.C. & Heatherly, L.
Partner: UNT Libraries Government Documents Department

High-beta studies in the ISX-B tokamak

Description: Experimental results from the ISX-B tokamak (major radius R/sub 0/=0.93 m, minor radius a=0.26 m, plasma current I/sub p/ 230 kA, elongation k=1.1 to 1.6, toroidal field B/sub phi/ less than or equal to 1.5 T, density anti n/sub e/ less than or equal to 1.1x10/sup 20/ m/sup -3/, neutral-beam power P/sub b/ less than or equal to 2.5 MW) at volume-averaged beta (<..beta..>) values up to 2.5% are described. Two aspects of these studies are presented: (1) empirical scaling of beta and of confinement time, and (2) MHD equilibrium analysis of ISX-B plasmas. The main points which are made are, respectively: (1) global confinement time tau/sub E/ exhibits a strong positive dependence on plasma current (I/sub p//sup 3/2/), a negative dependence on beam power (P/sub b//sup -2/3/), little or no dependence on <..beta..> or density, and no correlation with variations in the observed (m=1;n=1 dominated) MHD activity, and (2) profile analysis is coupled with an MHD equilibrium solver to obtain a model of the plasma consistent with profile, magnetic probe, and soft x-ray data, and with the boundary conditions imposed by the poloidal coil currents.
Date: January 1, 1982
Creator: Neilson, G.H.; Bates, S.C.; Bell, J.D.; Bush, C.E.; Carreras, B.A.; Charlton, L.A. et al.
Partner: UNT Libraries Government Documents Department