Workshop on Burning Plasma Science
Topical Group on Boundary Science

The edge parameters of current tokamaks are more than two orders of magnitude smaller than those required in a reactor. To bridge this gap, we will need well-tested predictive models of the plasma boundary. Some aspects of these models can be developed using non-burning plasma devices. Others, such as those listed below, can only be tested in a D-T fueled, predominantly alpha-heated device. Only in such a device can the boundary and core plasma consistency required in a reactor be examined. Similarly, the effects of disruptions and related 'off-normal' plasma events at reactor scale will require a burning-plasma-capable device to assess.

Topics for presentation and discussion:

  1. Power and particle exhaust in the burning plasma regime

    1. Characterization of PFC responses to plasma fluxes, including spatial and temporal peaks,

    2. Understanding of radiative scenarios,

    3. Development of models adequate for lower collisionality, e.g., that associated with advanced tokamak operation

    4. Consistency of boundary behavior with core plasma confinement,

      1. Can no longer study the two independently since good core operation implies higher power levels,

      2. Fueling and particle control needs for achieving required (e.g., higher than Greenwald) densities at high confinement.

      3. Tritium retention and removal

        1. Makes use of graphite questionable

        2. Options for burning plasma - compatible PFC materials and/or concepts

        3. Disruption effects at reactor-scale energies and ensuing plasma perturbations (impurity influx, runaway electron conversion)

        4. He transport, enrichment, pumping

        5. Impact of lost alphas on PFCs

          Other issues may also be discussed, as appropriate. Please feel free to make recommendations to the topical group coordinators.

           Daren Stotler, PPPL (dstotler@pppl.gov) and
          John Wesley, General Atomics (          wesley@apollo.gat.com)

           

          Disruption Issues (J. Wesley)

          Attached please find a second-draft version of "Disruption Issues and Opportunities for a Burning Plasma Science Experiment" that I'm authoring on behalf of the GA/DIII-D Disruption Science team (Dennis Whyte et al.). What's presently in this paper version is still mainly words, with reference to the ITER Physics Basis for the details. I plan to flesh the details out with graphics in a presentation and a final 'proceedings' version. Some relatively new and interesting data from DIII-D about disruption frequencies and mitigation means applicable to burning plasma experiments will be included in the presentation.

          Present text is for advance information and to show what I have in mind re 'Disruption Science'. I will highlight the science issues involved in my talk. Disruption cause (MHD instability) is not included: that's for the MHD group to cover. My intent is to cover the 'after-thermal-quench-onset' aspects of disruption science and to show the importance of disruption science to the attainment and investigation of BP science, and to also highlight the fact that disruptions in burning plasmas (inevitable, alas) also bring with them new and burning plasma-regime unique science aspects.

           

          Strawman Answers (D. Stotler)

          As I promised earlier in the week, find attached a set of strawman answers to the Burning Plasma Science Workshop's 5 questions. Again, the motivation for drafting this list & sending it out ahead of time is that our discussion time will be finite, if not short. When we start that discussion, we will need to have at least a rough idea of where we are & where we are going. Nothing in this text is sacred; everything can be discussed & rewritten.

          If those of you who are not attending the Workshop would like to send comments or other input, it would be best if I received that information by 5 PM EST on Friday, Dec. 8. I will be attempting to read my mail while in Austin, but no guarantees.

          For those who will be in Austin (& presumably in the Boundary Science Breakout Session), you can either do likewise, or make suggestions during the discussion period. We will endeavor to make that session as productive as possible so that at it's end, we all know what we've agreed upon.