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Stabilization of the axisymmetric instability in the PDX tokamak

Description: Passive stabilization, associated with the mutual inductances of the field shaping coils with the plasma and with each other, can stabilize the axisymmetric magnetohydrodynamic instability in the Princeton Poloidal Divertor Experiment device that was observed in earlier numerical studies.
Date: December 1, 1977
Creator: Jardin, S.C.
Partner: UNT Libraries Government Documents Department

Experimental determination of the vertical instability strength in PDX tokamak

Description: The instability strength of a diverted plasma with vertical elongation is measured for a range of the magnetic field decay index, -1.5 < n < +0.5, in the standard-D and inverted-D configurations. The range of the instability growth time is from one to four orders of magnitude greater than previously published results. When the plasma current is in the range, 170 to 310 ka, the instability can be suppressed by passive stabilization due to currents induced in a discrete coil system together with a moderate power (100 kw) active feedback system. The inverted-D configuration is three times more unstable than the standard-D configuration for the same ellipticity. The inverted-D configuration is destabilized by its negative triangularity and the standard-D is stabilized by its positive triangularity.
Date: July 1, 1982
Creator: Takahashi, H.; Bol, K.; Maeda, H.; Okabayashi, M. & Reusch, M.
Partner: UNT Libraries Government Documents Department

Preliminary particle scoop limiter measurements in PDX

Description: A plasma edge particle scoop limiter has been installed on the equator of the Princeton Divertor Experiment (PDX), a large tokamak. The scoop limiter is unique in that it is designed such that the plasma plugs the entrance throat thereby impeding the return flow of neutralized gas to the discharge. Neutral gas pressures of the order of 50 microns were measured inside the scoop. The pressure dependence on electron density in the scrapeoff plasma at the throat entrance was stronger than linear.
Date: August 1, 1981
Creator: Jacobsen, R.
Partner: UNT Libraries Government Documents Department

Vertical poloidal asymmetries of low-Z element radiation in the PDX tokamak

Description: Vertical poloidal asymmetries of hydrogen isotopes and low-Z impurity radiation in the PDX tokamak may be caused by poloidally asymmetric sources of these elements at gas inlet valves, limiters or vacuum vessel walls, asymmetric magnetic field geometry in the region beyond the plasma boundary, or by ion curvature drifts. Low ionization states of carbon (C II- C IV) are more easily influenced by edge conditions than is CV. Vertical poloidal asymmetries of CV are correlated with the direction of the toroidal field. The magnitude of the asymmetry agrees with the predictions of a quasifluid neoclassical model. Experimental data and numerical simulations are presented to investigate different models of impurity poloidal asymmetries.
Date: June 1, 1983
Creator: Brau, K.; Suckewer, S. & Wong, S.K.
Partner: UNT Libraries Government Documents Department

Reduction of recycling by pumping at the PDX limiter

Description: We have installed two arrays of Zr-Al getters adjacent to the PDX limiter to affect the pumping of neutrals formed in this region. The projected area of the getters is approximately 0.4% of the plasma area, and the measured H/sub 2/ pumping speed is 16,000 l/sec. During ohmic discharges, the getters reduced the electron density decay time from 340 to 180 msec. This result, combined with H/sub ..cap alpha..'/ data indicates that the recycling coefficient decreases by 10% or more.
Date: February 1, 1983
Creator: Cecchi, J.L.; Knize, R.J.; Dylla, H.F.; Fonck, R.J.; Owens, D.K. & Sredniawski, J.J.
Partner: UNT Libraries Government Documents Department

Mass-resolving charge-exchange system on PDX

Description: The PDX charge-exchange system is comprised of four, ten channel, mass-resolved, charge-exchange analyzers. Each analyzer is constructed with parallel electric and magnetic fields and is calibrated over an energy range of 0.5 to 40 keV. The mass rejection between hydrogen and deuterium has been measured as better than 1000 to 1. For ohmic heated discharges the system can provide single shot radial ion temperature profiles (4 point) with 1 msec time resolution. For neutral beam heated discharges complete radial and temporal profiles can be obtained in 2 to 4 shots. The system is also equipped with a vertically aimed diagnostic neutral beam to allow local ion-energy distribution measurements. This report describes the analyzer system and its calibration, and presents results from ohmic and neutral beam heated discharges.
Date: October 1, 1982
Creator: Davis, S.L.; Mueller, D. & Keane, C.J.
Partner: UNT Libraries Government Documents Department

PDX multichannel interferometer

Description: A 10 channel, 140 GHz homodyne interferometer is described for use on PDX. One feature of this interferometer is the separation of the signal source and electronics from the power splitters, delay line, and receiving systems. The latter is situated near the upper and lower vacuum ports between the toroidal field magnets. A second feature is the signal stabilization of the EIO source by means of an AFC system. The complete interferometer is described including block diagrams, circuit diagrams, test data, and magnetic field test conducted on the preamplifiers, microwave diodes, isolators, etc., to determine the extent of magnetic shielding required. The description of the tracking filters and digital phase display circuit is referenced to accompanying reports.
Date: October 1, 1980
Creator: Bitzer, R.; Ernst, W. & Cutsogeorge, G.
Partner: UNT Libraries Government Documents Department

Development of the ion source for PDX neutral beam injection

Description: The paper describes the development of the ion source for neutral beam injection heating of PDX plasma. After a brief description of the plasma generator, the performance characteristics of the source, with different types of grids, are described. Based on test stand results it is concluded that at least two different versions of the source should be able to meet and even exceed the neutral power and energy requirements expected out of PDX injectors.
Date: January 1, 1979
Creator: Menon, M.M.; Tsai, C.C.; Gardner, W.L.; Barber, G.C.; Haselton, H.H.; Ponte, N.S. et al.
Partner: UNT Libraries Government Documents Department

Soft x-ray measurements from the PDX tokamak

Description: Temporally and spatially-resolved profiles of the PDX soft x-ray spectra have been measured during single tokamak pulses of circular and divertor plasmas with a recently developed pulse height analyzer. This detection system incorporates an array of five vertically displaced sets of lithium-drifted silicon detectors, each consisting of three independent channels optimized for rapid data collection in adjacent energy regions. Simultaneous measurement of x-ray emission integrated along five chords of the plasma cross section can thereby be achieved. Abel inversion of these data yields temporally-resolved radial profiles of the local electron temperature from the slope of the continuum, concentrations of high-Z impurities from the characteristic line intensities, and a measure of Z/sub eff/ from the continuum intensity. The techniques of x-ray pulse height analysis, with illustrations featuring the results from the initial PDX circular plasma experiments are discussed in detail. In addition, comparisons between circular and divertor plasmas on PDX, derived from the x-ray measurements, are also presented.
Date: May 1, 1982
Creator: Silver, E.H.; Bitter, M.; Brau, K.; Eames, D.; Greenberger, A.; Hill, K.W. et al.
Partner: UNT Libraries Government Documents Department

DAS performance analysis

Description: This report begins with an overview of the Data Acquisition System (DAS), which supports several of PPPL's experimental devices. Performance measurements which were taken on DAS and the tools used to make them are then described.
Date: February 1, 1984
Creator: Bates, G.; Bodine, S.; Carroll, T. & Keller, M.
Partner: UNT Libraries Government Documents Department

In-situ impurity measurements in PDX Edge plasma

Description: The surface analysis station of PDX combines several surface analysis techniques (AES, XPS, SIMS) for in-situ measurement of impurity fluxes in the edge-plasma. The major impurities deposited on a sample surface during nondiverted PDX discharges are oxygen, titanium (limiter material) and chlorine. The impurity fluxes measured at different radial positions decreased by a factor of ten from the plasma edge to the wall. The sample surface collecting the impurity ions is located behind a circular aperture. The observed broadening of the deposition profile of Ti relative to the aperture diameter enables an estimate to be made of the ratio of charge state/energy of Ti ions in the edge plasma. Time-resolved analyses of the deposited impurities are presented which indicate that the time behavior for various impurities may be quite different for different impurity species. This aspect is discussed in relation to probable impurity release mechanisms.
Date: July 1, 1980
Creator: Staib, P.; Dylla, H.F. & Rossnagel, S.M.
Partner: UNT Libraries Government Documents Department

Disruption characteristics in PDX with limiter and divertor discharges

Description: A comparison has been made between the characteristics of disruptions with limiter and divertor configurations in PDX. A large data base on disruptions has been collected over four years of machine operation, and a total of 15,000 discharges are contained in the data file. It was found that divertor discharges have less disruptions during ramp up and flattop of the plasma current. However, for divertor discharges a large number of fast, low current disruptions take place during the current ramp down. These disruptions are probably caused by the deformation of the plasma shape.
Date: September 1, 1986
Creator: Couture, P. & McGuire, K.
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

PDX infrared TV camera system

Description: An infrared TV camera system has been developed for use on PDX. This system is capable of measuring the temporal and spatial energy deposition on the limiters and divertor neutralizer plates; time resolutions of 1 ms are achievable. The system has been used to measure the energy deposition on the PDX neutralizer plates and the temperature jump of limiter surfaces during a pulse. The energy scrapeoff layer is found to have characteristic dimensions of the order of a cm. The measurement of profiles is very sensitive to variations in the thermal emissivity of the surfaces.
Date: August 1, 1981
Creator: Jacobsen, R.A.
Partner: UNT Libraries Government Documents Department

Performance of the PDX neutral beam wall armor

Description: The PDX wall armor was designed to function as an inner wall thermal armor, a neutral beam diagnostic, and a large area inner toroidal plasma limiter. In this paper we discuss its thermal performance as wall armor during two years of PDX neutral beam heating experiments. During this period it provided sufficient inner wall protection to permit perpendicular heating injections into normal and disruptive plasmas as well as injections in the absence of plasma involving special experiments, calibrations, and tests important for the optimization and development of the PDX neutral beam injection system. Many of the design constraints and performance issues encountered in this work are relevant to the design of larger fusion devices.
Date: February 1, 1985
Creator: Kugel, H.W.; Eubank, H.P.; Kozub, T.A. & Williams, M.D.
Partner: UNT Libraries Government Documents Department

Particle and heat flux measurements in PDX edge plasmas

Description: This paper describes the use of novel combined Langmuir-calorimeter probes to measure edge plasma conditions near the midplane in PDX. The probes consisted of up to five Langmuir probes and up to two calorimeters. Single and double probe characteristics yield n/sub e/ and T/sub e/ which are compared with that derived from a triple probe analysis. The calorimeters measure heat flux in the electron and ion drift directions. This paper presents time-resolved radial profiles of n/sub e/, T/sub e/, V/sub F/ (floating potential), and P (heat flux) during high power neutral beam-heated, single-null discharges and circular scoop limiter discharges. The temporal dependence of these quantities displays the previous observed behavior with respect to gross discharge characteristics; however, an additional dependence on confinement mode has been observed. During the H-mode of energy confinement, a transient depression of n/sub e/, T/sub e/, and P occurs in the scrape-off plasma.
Date: December 1, 1983
Creator: Budny, R. & Manos, D.
Partner: UNT Libraries Government Documents Department

PDX experimental results in FY82

Description: This report presents a detailed summary of the major experimental results of PDX in FY82 and represents the efforts of the entire PDX group. Topics covered include ..beta..-scaling and fishbone studies, fluctuations, disruptions, impurities and impurity transport, power handling, limiter conditioning, edge studies, plasma fueling, counter-injection, and diagnostic development. A less detailed version will appear as the FY82 PDX contribution to the PPPL Annual Report.
Date: August 1, 1983
Creator: Kaye, S.M.; Bell, M.; Bol, K.; Bitter, M.; Buchenauer, D.; Budny, R. et al.
Partner: UNT Libraries Government Documents Department

Particle and energy transport in the plasma scrape-off zone and its impact on limiter design

Description: The design of limiters for fusion devices depends critically on the transport properties of the plasma edge. Recent data from Langmuir Probe experiments and calorimeter probe experiments on the Poloidal Divertor Experiment (PDX) have provided information about the transport of particles and energy in the edge region of a plasma. These data have been used as input to a simple one-dimensional model in which the particle and thermal diffusion coefficients are permitted to be functions of the density and temperature. The transport coefficients deduced from the data are then applied to the cases of the TFTR device and a device like FED/INTOR to predict the optimum design for limiters or pump limiters. The results indicate the optimum limiter should have a concave shape when viewed from the plasma. The effect of the uncertainties in the deduced coefficients on the optimum design performance are also discussed.
Date: March 1, 1983
Creator: Ulrickson, M. & Post, D.E.
Partner: UNT Libraries Government Documents Department

Passive stabilization in a linear MHD stability code

Description: Utilizing a Galerkin procedure to calculate the vacuum contribution to the ideal MHD Lagrangian, the implementation of realistic boundary conditions are described in a linear stability code. The procedure permits calculation of the effect of arbitrary conducting structure on ideal MHD instabilities, as opposed to the prior use of an encircling shell. The passive stabilization of conducting coils on the tokamak vertical instability is calculated within the PEST code and gives excellent agreement with 2-D time dependent simulations of PDX.
Date: March 1, 1980
Creator: Todd, A.M.M.
Partner: UNT Libraries Government Documents Department

PDX neutral-beam reionization losses

Description: Reionization losses for 1.5 MW H/sup 0/ and 2 MW D/sup 0/ neutral beams injected into the PDX tokamak were studied using pressure gauges, photo-transistors, thermocouples, surface shielding, and surface sample analysis. Considerable outgassing of conventionally prepared 304SS ducts occurred during initial injections and gradually decreased with the cumulative absorption of beam power. Reionization power losses are presently about 5% in the ducts and about 12% total for a beamline including the duct. Present duct pressures are attributed primarily to gas from the ion source and neutralizer with much smaller contributions from residual wall desorption. Physical mechanisms for the observed duct outgassing are discussed.
Date: February 1, 1982
Creator: Kugel, H.W.; Dylla, H.F.; Eubank, H.P.; Kozub, T.A.; Moore, R.; Schilling, G. et al.
Partner: UNT Libraries Government Documents Department

Plasma rotation in the PDX tokamak

Description: Toroidal and poloidal rotation has been measured in the Poloidal Divertor Experiment (PDX) tokamak in ohmic- and neutral-beam-heated plasmas in a variety of discharge conditions and in both circular and diverted configurations. Rotation velocities were deduced from Doppler shifts of magnetic dipole (M1) lines and lines of optically allowed transitions in the visible and uv regions, from K/sub ..cap alpha../ emission, and also from an array of magnetic pickup loops. Poloidal and toroidal rotation velocities in ohmically heated discharges were unusually less than 3 x 10/sup 5/ cm/sec. Near the plasma edge the toroidal-rotation velocity varies with poloidal angle both before and during neutral-beam injection. No systematic poloidal rotation was observed during neutral-beam injection centered about or displaced 10 cm from the horizontal midplane, which implies that the poloidal damping time tau/sub theta/ < 0.5 tau/sub ii/, consistent with theoretical estimates.
Date: June 1, 1983
Creator: Brau, K.; Bitter, M.; Goldston, R.J.; Manos, D.; McGuire, K. & Suckewer, S.
Partner: UNT Libraries Government Documents Department

Millimeter radiometer techniques for plasma temperature diagnostics

Description: Radiometers have been employed in radio telescopes to measure stellar plasma temperatures. However, when electron temperature measurements are made on hot dense plasmas in thermonuclear fusion research, radiometry techniques are modified. This report discusses these modifications as they are incorporated in radiometers on the PLT device. Included is a list of proposed radiometer developments and techniques for the PLT, PDX, and TFTR devices.
Date: November 1, 1979
Creator: Bitzer, R.A.
Partner: UNT Libraries Government Documents Department

He/sup + +/ transport in the PDX tokamak

Description: A powerful new approach to the study of particle transport and helium ash confinement in high-temperature fusion plasmas is demonstrated by charge-exchange recombination spectroscopy of He/sup + +/ in ohmically heated PDX discharges. Time and space resolved measurements of He/sup + +/ density following a short puff of helium gas into the plasma edge are fitted using a diffusive/convective transport model with coefficients D = (2.1 +- 0.9) x 10/sup 4/ cm/sup 2/ s/sup -1/ and v(r)/D = (0.8 +- 0.3) delta (ln n/sub e/)/deltar.
Date: December 1, 1983
Creator: Fonck, R.J. & Hulse, R.A.
Partner: UNT Libraries Government Documents Department

Titanium density measurements in the PDX Tokamak using TiXVII forbidden line

Description: A spectrum line observed at 3834.4 +- 0.2 A and identified as a 2s/sup 2/2p/sup 2/ /sup 3/P/sub 2/ ..-->.. /sup 3/P/sub 1/ magnetic dipole transition in the TiXVII ground configuration, was used for titanium density measurements in the Poloidal Divertor Experiment (PDX).
Date: July 1, 1979
Creator: Suckewer, S.; Hinnov, E. & Bol, K.
Partner: UNT Libraries Government Documents Department