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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

Far-infrared interferometry/polarimetry on the ISX-B tokamak

Description: Theoretical analyses have shown that the current density distribution in a tokamak plasma can be obtained indirectly by the measurement of the poloidal magnetic field created by the current flowing in the plasma discharge. The distribution of this field may be determined by projecting linearly polarized far-infrared (FIR) laser beams through the plasma and measuring the Faraday rotation of the polarization. Since the rotation angle of the polarization vector is proportional to the line integral of electron density times the poloidal magnetic field along the path, the electron density profile must also be measured simultaneously in order to unfold the current distribution. The amount of Faraday rotation expected in a typical plasma experiment is calculated to be on the order of 5 to 10 degrees. Therefore the authors have constructed a multichord modulated FIR polarimeter/interferometer that measures both the phase delay of four laser beams passing through a plasma discharge and the instantaneous polarization of these same beams. The phase shift of each of the beams is directly proportional to the line-averaged electron density and the polarization rotation is directly proportional to the line-averaged density times poloidal field.
Date: January 1, 1984
Creator: Hutchinson, D.P.; Ma, C.H.; Staats, P.A. & Vander Sluis, K.L.
Partner: UNT Libraries Government Documents Department

PLT and ISX neutral beam injectors

Description: Six high power (40 keV--60 A) injection systems, four for PLT (Princeton Plasma Physics Laboratory) and two for ISX (Oak Ridge National Laboratory) tokamaks, have been developed, fabricated, and operated. Each injector delivers 750 kW (1000 kW) of H (D) neutral power to the tokamak plasma. An in-depth system parameter study has revealed unique features: high atomic yield (approximately 85%), improved ion optics due to a preacceleration technique, near steady-state operation (up to 500 msec), and a possible technique to control species yield. Routine operation includes high duty cycle (approximately 10%), long filament lifetime (several months), high arc efficiency, and the reliability necessary for application on a fusion device. The program status and injection parameters will be discussed.
Date: January 1, 1978
Creator: Haselton, H H; Barber, G C & Becraft, W R
Partner: UNT Libraries Government Documents Department

Recalling ISX shot data files from the off-line archive

Description: This document describes a set of computer programs designed to allow access to ISX shot data files stored on off-line disk packs. The programs accept user requests for data files and build a queue of end requests. When an operator is available to mount the necessary disk packs, the system copies the requested files to an on-line disk area. The program runs on the Fusion Energy Division's DECsystem-10 computer. The request queue is implemented under the System 1022 data base management system. The support programs are coded in MACRO-10 and FORTRAN-10.
Date: February 1, 1981
Creator: Stanton, J.S.
Partner: UNT Libraries Government Documents Department

Langmuir probe measurements of the scrape-off plasma in ISX-A

Description: A fixed double Langmuir probe was used to investigate the temporal behavior of the scrape-off plasma in the ISX-A tokamak. During gas puffing, the ion saturation current dropped rapidly to a very low level while the line average density showed a steady increase. This sudden transition was due mainly to a density change of more than a factor of five while the electron temperature remained relatively constant at approximately 10 eV. This behavior was easily observed at points away from the limiter with mild and moderate gas puffing rates, and near the inner edge of the limiter with strong gas puffing. In order to explain the phenomenon, it is suggested that there may be two distinct layers in the scrape-off plasma and that the boundary between the layers moves inward toward the limiter. The existence of the boundary has been confirmed indirectly by sudden shifts of the plasma during feedback control experiments.
Date: November 1, 1978
Creator: Namkung, W.; England, A. C. & Eldridge, O. C.
Partner: UNT Libraries Government Documents Department

Discharge cleaning and plasma purity in ISX-B

Description: Two simply measured parameters are shown to be useful in characterizing the vacuum vessel and plasma cleanliness and in predicting plasma performance in the ISX-B tokamak. It is demonstrated that the parameter P/sub rad//anti n/sub e/, measured at the start of each tokamak discharge, is related to both the available operating space (I/sub p/, anti n/sub e/) with Ohmic heating and the energy confinement times achieved with neutral beam injection. An assessment of P/sub rad//anti n/sub e/ on both a shot-to-shot and a day-to-day basis then determines the changing cleanliness of the plasma. It is further shown that P/sub rad//anti n/sub e/ can be predicted by the results of a residual gas analysis performed after discharge cleaning; specifically, it is directly proportional to the fractional concentration of water vapor.
Date: January 1, 1984
Creator: Wootton, A.J. & Mioduszewski, P.K.
Partner: UNT Libraries Government Documents Department

Tokamak instrumentation and controls

Description: The three areas of study emphasis to date are: (1) Physics implications for controls, (2) Computer simulation, and (3) Shutdown/aborts. This document reports on the FY 78 efforts (the first year of these studies) to address these problems. Transient scenario options for the startup of a tokamak are developed, and the implications for the control system are discussed. This document also presents a hybrid computer simulation (analog and digital) of the Impurity Study Experiment (ISX-B) which is now being used for corroborative controls investigations. The simulation will be expanded to represent a TNS/ETF machine.
Date: February 1, 1979
Creator: Becraft, W. R.; Bettis, E. S.; Houlberg, W. A.; Onega, R. J. & Stone, R. S.
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