Distinguishing Gyro-Bohm and Bohm scaling in stellarators (open access)

Distinguishing Gyro-Bohm and Bohm scaling in stellarators

With statistical analysis of global data from one, two and four stellarators, it is possible to draw limited conclusions whether Gyro- Bohm or Bohm scaling prevails. Either scaling may be favored, depending on whether corrections are included for possible {Beta} and v{sub *} corrections and whether all data are taken, or selected cases with low collisionality, or low net toroidal current, or with ECH heating applied, and so on. Monte Carlo-like simulations are used to test reliability of inferences about power-law scaling exponents made from data having substantial statistical variance and collinearity of control parameters. These show that for reliable conclusions, statistical studies should be augmented; more directed experimental studies are needed, with well controlled discharges and radially resolved data - such as those already begun on ATF and W7-AS.
Date: May 5, 1993
Creator: Dory, R.A.; Murakami, M. & Stroth, U.
Object Type: Article
System: The UNT Digital Library
Human Factors evaluation of LCS 254 and 255 (open access)

Human Factors evaluation of LCS 254 and 255

This report includes the results of the Human Factors evaluation of the local control stations (LCS) 254 and 255 performed by Savannah River Technology Center (SRTC) Human Factors. Recommendations are included in order that the panel designs will be upgraded to comply with human engineering design guidelines. Figures 1 and 2 are included as examples of recommended changes. Also, consideration was given to including the proposed engineering changes which are currently on-going for LCS 255. Appendix A identifies the human engineering requirements from NUREG-0700 which were used in the evaluation process, and the areas of the design which do not comply with the guidelines. Those areas of the panel design which fail to comply with the human engineering guidelines are label location, label content, location aids, panel layout, and control display integration. Each of these design deficiencies and proposed corrections are described in this report.
Date: May 5, 1993
Creator: Goffe, L. & Held, J. E.
Object Type: Report
System: The UNT Digital Library
Japan's Foreign Aid (open access)

Japan's Foreign Aid

Japan has quickly risen to prominence as a donor of official development assistance (ODA), providing volumes of aid on par with the United States since the late 1980s. Originally a tool to bolster Japan's postwar economic recovery, Japanese aid has gradually assumed importance as a foreign policy tool. Faced with increased pressure from the international community to play a greater role in meeting global challenges and lacking the military and diplomatic resources of other nations, Japan has increasingly turned to its foreign aid as a source of world influence.
Date: May 5, 1993
Creator: Hankes, Nancy J
Object Type: Report
System: The UNT Digital Library
Measurement of source tube radial position in cast EMC testbeam module (open access)

Measurement of source tube radial position in cast EMC testbeam module

Using a {sup 137}Cs source we have determined the position of two of the source tubes embedded in the Pb absorber in the cast EMC module used in the Fermilab test beam. Two scintillator tiles placed in the gaps on both sides of an absorber containing a source tube were readout into independent phototubes. The difference in scintillator response was measured in two towers at two different source tube layers. We find the source tube to be displaced towards the (radial) front of the EMC by about 1.6 mm in both measurements. Work is proceeding now to check other source tubes in other locations.
Date: May 5, 1993
Creator: Jankowski, D. J. & Stanek, R.
Object Type: Report
System: The UNT Digital Library
New techniques in 3D scalar and vector field visualization (open access)

New techniques in 3D scalar and vector field visualization

At Lawrence Livermore National Laboratory (LLNL) we have recently developed several techniques for volume visualization of scalar and vector fields, all of which use back-to-front compositing. The first renders volume density clouds by compositing polyhedral volume cells or their faces. The second is a ``splatting`` scheme which composites textures used to reconstruct the scalar or vector fields. One version calculates the necessary texture values in software, and another takes advantage of hardware texture mapping. The next technique renders contour surface polygons using semi-transparent textures, which adjust appropriately when the surfaces deform in a flow, or change topology. The final one renders the ``flow volume`` of smoke or dye tracer swept out by a fluid flowing through a small generating polygon. All of these techniques are applied to a climate model data set, to visualize cloud density and wind velocity.
Date: May 5, 1993
Creator: Max, N.; Crawfis, R. & Becker, B.
Object Type: Article
System: The UNT Digital Library
Radiative divertor modeling studies (open access)

Radiative divertor modeling studies

A two-dimensional fluid code called UEDGE is used to simulate the edge plasma in tokamak divertors and to evaluate methods for reducing the heat load on divertor plates by radiating some of the power before it reaches the plates. UEDGE is a fully-implicit code being developed jointly by us, D. A. Knoll and R. B. Campbell. For these studies, UEDGE uses a banded matrix solver and a fixed-fraction impurity model. Work is presently underway with Knoll and Campbell to include a memory-efficient iterative solver and a model of impurity transport. Simulations of the proposed TPX device show that a few percent nitrogen concentration in the scrape-off layer can radiate up to 80% of the divertor power, thus reducing the peak heat flux and electron temperature at the divertor plate to acceptable values. A comparison of the neutral gas distribution from UEDGE with results from the DEGAS Monte Carlo neutrals code confirms the validity of our fluid neutrals model.
Date: May 5, 1993
Creator: Rensink, M. E.; Allen, S. L.; Hill, D. N.; Kaiser, T. B. & Rognlien, T. D.
Object Type: Article
System: The UNT Digital Library
Recent developments on ECR sources at LBL (open access)

Recent developments on ECR sources at LBL

After a number of refinements, the stability and ease of tuning of the LBL AECR ion source are greatly improved. Several nuclear science experiments have now used cyclotron ion beams injected by the AECR ion source and have taken advantage of its good short and long term-stability and high performance. Refinements include installation of a dc filament power supply for the electron gun, improved gas flow control.and temperature stabilization of parts of the microwave transmission network. Measurements of the mean plasma potential and plasma potential difference were made on the AECR and the LBL ECR sources. The absolute. mean potentials of plasmas of oxygen, argon, and argon mixed with oxygen in the AECR have been determined. These plasma potentials are positive with respect to the plasma wall and are on the order of a few tens of volts for microwave power up to 600 W and normal operating gas flow. Electrons injected by an electron gun into the AECR plasma reduce the plasma potentials. Beam energy spreads of oxygen, argon and argon mixed with oxygen have also been measured. Measurement of the plasma potential difference between the first and the second stage of the LBL ECR ion source shows that …
Date: May 5, 1993
Creator: Xie, Z. Q. & Lyneis, C. M.
Object Type: Article
System: The UNT Digital Library
Status of {alpha}{sub s} measurements (open access)

Status of {alpha}{sub s} measurements

I review the current determinations of {alpha}{sub s}. Attention is given to the theoretical uncertainties inherent in most determinations. all current determinations are consistent with an average of {alpha}{sub s}(M{sub Z}) = 0.119{plus_minus}0.005. Prospects for reduction of the errors in the future are discussed.
Date: May 5, 1993
Creator: Hinchliffe, I.
Object Type: Article
System: The UNT Digital Library