DEGAS 2 Presentations and Papers

• Sherwood Meeting, Philadelphia, PA, 1996
  • Charles Karney's poster titled "Scoring in DEGAS 2",
  • Daren Stotler's poster titled "Atomic and Surface Physics Data in DEGAS 2",
  • Much of this material has since been incorporated into the User's Manual.
• IAEA Meeting, Montreal, Canada, 1996
  • The paper, entitled "DEGAS 2 Neutral Transport Modeling of High Density, Low Temperature Plasmas" was published in Proceedings of the Sixteenth International Conference on Plasma Physics and Controlled Nuclear Fusion Research, (Montreal, Canada, September 1996) (International Atomic Energy Agency, Vienna, Austria, 1997), Vol. 2, p. 633-639.
  • A preprint version is available as PPPL Report, PPPL-3221 in PostScript or PDF format.
• APS-DPP Meeting, Denver, CO, 1996
  • Presented a poster titled "DEGAS 2 Neutral Transport Modeling of High Density, Low Temperature Plasmas"
• International Conference on Computational Physics, San Jose, CA, 1997
  • Charles Karney presented a poster titled "Hybrid Simulation of Neutral Gas Interacting with a Plasma", available in PDF or Postscript format.
• APS-DPP Meeting, Pittsburgh, PA, 1997
  • Charles Karney's poster titled "Advances in Neutral Transport Modeling with DEGAS 2" is availabled here as ugly html or as a prettier PostScript format in a tar file.)
  • Daren Stotler's poster titled "DEGAS 2 Modeling of Spatial and Spectral Distributions of Line Emissions in Alcator C-Mod" can also be found in HTML format or as PostScript in a tar file.)
• 13th Plasma Surface Interactions Conference, San Diego, CA, 1998
  • The paper, "B2-EIRENE Simulations of the Death Ray in Alcator C-Mod" (no DEGAS 2 work here, yet :-) was published in J. Nucl. Mater. 266 - 269 (1999) 947.
  • The corresponding poster is available as a PDF file.
  • A separate poster discusses the original DEGAS 2 - EIRENE benchmark.
• Computational Research in Princeton seminar, July 17, 1998
  • Charles Karney described in a talk the random number generator used by DEGAS 2.
• 12th Topical Conference on High-Temperature Plasma Diagnostics, Princeton, NJ, 1998
  • The paper entitled "Spectroscopic Measurements of Hydrogen Ion Temperature During Divertor Recombination" was published in Review of Scientific Instruments 70 (1999) 344.
  • The poster is available as a PDF or PostScript file.
• 7th International Workshop on Plasma Edge Theory in Fusion Devices, Tajimi, Japan, 1999
  • The paper entitled "Coupling of Parallelized DEGAS 2 and UEDGE Codes" was published in Contrib. Plasma Phys. 40 (2000) 221.
  • The poster, in PDF format, is pretty complete.
• 14th Plasma Surface Interactions Conference, Rosenheim, Germany, 2000
  • All of these are PDF files. If you require another format, please let us know.
  • This paper represents modeling work carried out in support of the experimental paper given by Spencer Pitcher (MIT-PSFC). The above poster has, for clarity, a few slides borrowed from Spencer's invited talk.
  • The DEGAS 2 simulations are described in the paper titled "Modeling of Alcator C-Mod Divertor Baffling Experiments", available as PPPL Report, PPPL-3523,
  • Later published in J. Nucl. Mater. 290 - 293 (2001) 967.
  • The poster contains additional information and color plots.
• PPPL Computational Plasma Physics Group Seminar, June 13, 2000
  • Title: "Use of FWEB in DEGAS 2 to Expedite Documentation and Maintainability"
  • This talk describes several of the ways that FWEB is used in DEGAS 2 with specific examples from the code.
• APS-DPP Meeting, Quebec, Canada, 2000
  • Essentially a repeat of the information presented at the 2000 PSI; see the link to that paper above for details.
  • The poster has a few new wrinkles that experts will be interested in.
• APS-DPP Meeting, Long Beach, California, 2001
  • Title: "Neutral Gas Transport Simulations of Gas Puff Imaging Experiments on NSTX and Alcator C-Mod"
  • This is a preliminary look at material to be presented at the 2002 Plasma Surface Interactions Conference, Gifu, Japan.
  • The poster is a bit large (1.5 MB), but pretty detailed.
• 13th APS Topical Conference on Atomic Processes in Plasmas
  • An invited talk titled "Understanding of Neutral Gas Transport in the Alcator C-Mod Tokamak Divertor" represents the conclusion of the work reported at the 14th Plasma Surface Interactions Conference.
  • The talk slides are available here in PDF format. Anyone interested in seeing the corresponding PowerPoint slides and movies should mail me.
  • The paper is available as a PPPL Report,
  • It will be published in AIP Conference Proceedings.
• 15th Plasma Surface Interactions Conference, Gifu, Japan, 2002
  • This paper, titled "Neutral Transport Simulations of Gas Puff Imaging Experiments on Alcator C-Mod", was promised at the Long Beach APS-DPP meeting. However, because of length restrictions and interesting complications provided by molecular contributions to the Balmer-alpha emission, only the simulations of Alcator C-Mod were discussed.
  • The poster has some extra detail and plots that did not fit into the paper.
  • The paper is available as a PPPL Report.
  • It will eventually be published in J. Nucl. Mater..
• APS-DPP Meeting, Orlando, Florida, 2002
  • Title: "Neutral Transport Simulations of Gas Puff Imaging Experiments on NSTX"
  • This poster focuses more on the impact of plasma perturbations on the neutral density profile and the consequences for the spatial structure of the emission patterns.
  • The poster is huge (8 MB), hence, you will be much better off downloading it rather than reading it online.
• 9th International Workshop on Plasma Edge Theory in Fusion Devices, San Diego, California, 2003
  • Title: "Three-Dimensional Neutral Transport Simulations of Gas Puff Imaging Experiments"
  • This paper and poster describes 3-D extensions to the NSTX modeling of Gas Puff Imaging experiments reported at the 2002 APS-DPP meeting. The principal addition was the emulation of the 81 x 161 pixel camera. This allowed direct benchmarking of the simulations and a quantitative estimate of the effect of the toroidal extent of the gas cloud on radial resolution.
  • Following the PET Workshop, a smaller, 1 day "US-Japan Workshop on Spatiotemporal Description of Edge Plasma Transport in Theory and Experiment" was held. This talk provides an overview of the GPI experiments on NSTX and Alcator C-Mod, as well as some of the efforts to analyze and simulate those experiments. This PDF file does not, of course, contain the movies. However, the GPI movies can be accessed from Stewart Zweben's web site.
• APS-DPP Meeting, Albuquerque, New Mexico, 2003
  • Title: "Neutral Transport Simulations of Gas Puff Imaging Experiments on NSTX"
  • This poster is very similar to the one presented at PET 9. New additions include a 3-D visualization (you may need the DivX codec to view this movie) and some further analysis of the variation of the experimental emission cloud orientation. Be warned that this file is 5 MB.
• 16th Plasma Surface Interactions Conference, Portland, Maine, 2004
  • The abstract for this meeting was entitled "Three-Dimensional Simulation of Gas Conductance Measurement Experiments on Alcator C-Mod and NSTX". Earlier simulations of the divertor bypass experiments (e.g., see my 2000 PSI paper and Steve Lisgo's thesis) used approximate representations of the C-Mod subdivertor. Brian LaBombard performed some measurements of gas flows through these structures to permit quantitative benchmarks of the neutral transport codes. This paper was intended to document DEGAS 2 simulations of those experiments and some analogous simulations of NSTX.
  • For various reasons, the NSTX work was not completed in time for the conference and was omitted from the paper. Plus, the conference's length constraints were strained by the inclusion of a separate (and very instructive) benchmarking of the code against gas flow in a rectangular pipe. So, the final title of the paper is "Three-Dimensional Simulation of Gas Conductance Measurement Experiments on Alcator C-Mod". The PDF version of the paper is now available as a PPPL report and will later be published in the Journal of Nuclear Materials.
  • The poster goes over the same material in a little more depth and includes a few slides introducing the NSTX work still to be done.
• APS-DPP Meeting, Savannah, Georgia, 2004
  • Title: "Three-Dimensional Simulation of Gas Conductance Measurement Experiments on NSTX and Alcator C-Mod".
  • This poster is largely the same material as the above PSI poster. The introductory material has a different emphasis since the objective is now to do neutral transport simulations in NSTX. Some additional refinements since PSI have been included, although the C-Mod and pipe-flow simulations are ongoing.
• Workshop on New Directions for Advanced Computer Simulations and Experiments in Fusion-Related Plasma-Surface Interactions (PSIF), Oak Ridge, Tennessee, 2005
  • Title: "Plasma-Surface Interaction Processes in a Neutral Transport Code - What's Not in the Model".
  • The workshop was organized to identify plasma-material interaction data needs and to assess the current and future state of experimental and computational approaches to obtaining those data.
  • This talk briefly described the PMI model currently used in DEGAS 2 and listed some of the various pieces of physics not handled by that model.
• 2005 Transport Task Force Meeting, Napa, California, 2005
  • Title: "Why Should I Believe My Code? - The Quest for Verification & Validation".
  • This was an invited, preview talk discussing the verification and validation of DEGAS 2. Suggestions for going further, particularly with regard to dedicated validation experiments, were also made.
  • The workshop also featured two parallel working sessions devoted to verification and validation presentations and discussions. Those interested in learning more should check the TTF web site; PDF versions of the talks have been promised.
• IAEA Technical Meeting: Establishment of A+M Computer Code Network, Vienna, Austria, 2005
  • Title: "Atomic & Molecular Data Usage in the DEGAS 2 Monte Carlo Neutral Transport Code".
  • This basic talk describes the atomic and molecular (and, to a lesser extent, the plasma-material interaction) data used in DEGAS 2, where they came from and how they were processed into DEGAS 2's format.
  • For more on atomic data for fusion (and, eventually for the product of this meeting), check out the IAEA Atomic and Molecular Data Unit's home page.
• 2006 Transport Task Force Meeting, Myrtle Beach, South Carolina, 2006
  • Title: "An Example 'Reference Problem' for Code Verification".
  • This is a follow-on to the verification and validation activity that began at the 2005 Transport Task Force Meeting. In particular, at and following that meeting, the Edge Coordinating Committee proposed to collect a set of "reference problems" to be used in testing edge simulation codes. This talk describes the proposed format for the reference problem and provides an example of one.
• 17th Plasma Surface Interactions Conference, Hefei, China, 2006
  • Title: "Details of Neutral Transport in Gas Puff Imaging Experiments".
  • The rather nebulous title is the result of trying to cover two almost separate topics in one paper. The first topic is an investigation of the validity and time resolution provided by the helium collisional radiative models. This analysis largely relies on criteria derived by Greenland and is carried out for GPI-relevant parameters. The happy result is that the familiar single state CR model is valid for the parameters of interest and provides the microsecond level of time resolution needed. The second topic is a second attempt at the 3-D simulations begun in 2003 (see paper presented at the 9th PET Workshop). As a result of more thorough geometric calibrations of the GPI camera and of a quantification of the nonlinearity in the camera response, the comparison here is vastly improved. In fact, the remaining discrepancies are well within the error bars.
  • The poster has slightly more material than the paper.
  • The conference referee's numerous comments on the paper led to a reexamination of some questions left open in the original version of the paper. Somewhat surprisingly, these questions were largely answered with a modest amount of work, resulting in a vastly improved paper.
• 2006 Atomic, Molecular, Optical Sciences Research Meeting, Warrenton, Virginia, 2006
  • Title: "Atomic Physics in ITER - The Foundation for the Next Step to Fusion Power"
  • This talk provides an introduction to the key roles played by atomic physics processes in ITER and fusion devices in general. Much of the emphasis is on edge and divertor plasmas, although three core plasma diagnostics with strong atomic physics connections are also discussed.
  • Note that there is not much specific discussion of DEGAS 2 here, although EIRENE does appear in a few places. Nonetheless, some of these atomic physics processes are already in DEGAS 2; the remainder will be or could be incorporated into the code.
• 5th International Conference on Atomic and Molecular Data and Their Applications (ICAMDATA), Meudon, France, 2006
  • Title: "Atomic Physics in ITER - The Foundation for the Next Step to Fusion Power"
  • This invited keynote talk is similar to the one presented at the AMOS meeting, but is 15 minutes shorter and includes an introduction to the ITER experiment. The same comments apply; i.e., there is very little DEGAS 2 related material here.
  • There is an associated paper that will be published with the conference proceedings by AIP.
  • While in Paris, a second talk was presented at the LIMHP. This is essentially the same as the one given at PSIF, slightly updated and with a little more introductory material.
• APS-DPP Meeting, Philadelphia, Pennsylvania, 2006
  • Title: "Validation of DEGAS 2 with NSTX Gas Puff Imaging Experiments"
  • This poster covers the revised DEGAS 2 simulations described in the final PSI paper, providing additional details and improvements made following the Hefei PSI conference.
  • A secondary purpose of this presentation is to begin a more serious discussion of code validation. The rather affirmative sounding title for the poster is misleading. Instead, the intent is to underscore the need for quantitative measures of code validation and to illustrate how achieving that objective requires more careful analysis than the more familiar qualitative approaches to "validation".
• 2007 Transport Task Force Meeting, San Diego, California, 2007
  • Title: "A Step Closer to a Validation Exercise"
  • This talk and poster pick up with the validation discussion begun in the poster at the 2006 APS-DPP meeting. Validation metrics are discussed in more detail, and two are evaluated using the data from the DEGAS 2 simulations of the NSTX Gas Puff Imaging experiments. However, the assumptions of these metrics are not applicable to this situation. Hence, these metric evaluations are suitable only as examples.
  • Note that the talk consists of slides 1 through 9 in this file; the poster utilized all 17.
• ARIES Town Meeting on "Edge Plasma Physics and Plasma Material Interactions in the Fusion Power Plant Regime", 2010
  • Title: "Neutral Transport from Wall to Scrape-Off Layer"
  • This invited talk provides an overview of neutral sources and transport, emphasizing their role in ITER and fusion power plants.
• 19th Plasma Surface Interactions Conference, San Diego, California, 2010 & APS-DPP Meeting, Chicago, Illinois, 2010
  • Title: "Simulations of Diffusive Lithium Evaporation onto the NSTX Vessel Walls"
  • The poster and paper presented at the PSI meeting describes DEGAS 2 simulations of the evaporation of lithium into the (gaseous) helium filled NSTX vacuum vessel. The objective of the modeling was to concoct an optimized prescription for coating all of the plasma facing tiles with lithium.
  • Because of the relative simplicity of the model, these simulations and the associated experiments also made for a nice validation example.
  • The final paper and the contemporaneous poster at the 2010 APS-DPP meeting incorporate revisions prompted by comments from the PSI reviewers.
• " Comparison of Gas Puff Imaging Data in NSTX with DEGAS 2 Simulations ", B. Cao, D. P. Stotler, S. J. Zweben, M. Bell, A. Diallo, and B. LeBlanc.
  • This latest in the series of comparisons of DEGAS 2 with GPI data was carried out by Chinese visitor Bin Cao.
  • The radial profiles of the observed and simulated light emission agreed to within the estimated uncertainties, about 0.3 cm, as in the 2006 comparison.
  • However, absoluted calibrations of the GPI camera and gas puffing system allowed a quantitative comparison of the number of photons seen by the camera per puffed deuterium atom. The experimental result was 1/89 photons per atom (+/- 34%), while DEGAS 2 yielded 1/75 +/-18%; again, the results are within the estimated uncertainties.
  • The paper describing this work can be obtained as a PPPL report or as a journal article (Fusion Science and Technology, to appear July 2013).