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Title: An overview of recent physics results from NSTX

Currently, the National Spherical Torus Experiment (NSTX) is being upgraded to operate at twice the toroidal field and plasma current (up to 1 T and 2 MA), with a second, more tangentially aimed neutral beam (NB) for current and rotation control, allowing for pulse lengths up to 5 s. Recent NSTX physics analyses have addressed topics that will allow NSTX-Upgrade to achieve the research goals critical to a Fusion Nuclear Science Facility. These include producing stable, 100% non-inductive operation in high-performance plasmas, assessing plasma-material interface (PMI) solutions to handle the high heat loads expected in the next-step devices and exploring the unique spherical torus (ST) parameter regimes to advance predictive capability. Non-inductive operation and current profile control in NSTX-U will be facilitated by co-axial helicity injection (CHI) as well as radio frequency (RF) and NB heating. CHI studies using NIMROD indicate that the reconnection process is consistent with the 2D Sweet-Parker theory. Full-wave AORSA simulations show that RF power losses in the scrape-off layer (SOL) increase significantly for both NSTX and NSTX-U when the launched waves propagate in the SOL. Moreover, Toroidal Alfven eigenmode avalanches and higher frequency Alfven eigenmodes can affect NB-driven current through energy loss and redistribution ofmore » fast ions. The inclusion of rotation and kinetic resonances, which depend on collisionality, is necessary for predicting experimental stability thresholds of fast growing ideal wall and resistive wall modes. Neutral beams and neoclassical toroidal viscosity generated from applied 3D fields can be used as actuators to produce rotation profiles optimized for global stability. DEGAS-2 has been used to study the dependence of gas penetration on SOL temperatures and densities for the MGI system being implemented on the Upgrade for disruption mitigation. PMI studies have focused on the effect of ELMs and 3D fields on plasma detachment and heat flux handling. Simulations indicate that snowflake and impurity seeded radiative divertors are candidates for heat flux mitigation in NSTX-U. Studies of lithium evaporation on graphite surfaces indicate that lithium increases oxygen surface concentrations on graphite, and deuterium-oxygen affinity, which increases deuterium pumping and reduces recycling. In situ and test-stand experiments of lithiated graphite and molybdenum indicate temperature-enhanced sputtering, although that test-stand studies also show the potential for heat flux reduction through lithium vapour shielding. Non-linear gyro kinetic simulations have indicated that ion transport can be enhanced by a shear-flow instability, and that non-local effects are necessary to explain the observed rapid changes in plasma turbulence. Predictive simulations have shown agreement between a microtearing-based reduced transport model and the measured electron temperatures in a microtearing unstable regime. Finally, two Alfven eigenmode-driven fast ion transport models have been developed and successfully benchmarked against NSTX data. Upgrade construction is moving on schedule with initial physics research operation of NSTX-U planned for mid-2015.« less
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  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Univ. of Illinois, Urbana-Champaign, IL (United States)
  4. Univ. of California, Davis, CA (United States)
  5. Columbia Univ., New York, NY (United States)
  6. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  7. IPP, Garching (Germany)
  8. Univ. of California, San Diego, CA (United States)
  9. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  10. Univ. of Tennessee, Knoxville, TN (United States)
  11. Princeton Univ., NJ (United States)
  12. Purdue Univ., West Lafayette, IN (United States)
  13. General Atomics, San Diego, CA (United States)
  14. Univ. of California, Los Angeles, CA (United States)
  15. Lodestar Research Corp., Boulder, CO (United States)
  16. Johns Hopkins Univ., Baltimore, MD (United States)
  17. Univ. of Wisconsin, Madison, WI (United States)
  18. Univ. of Washington, Seattle, WA (United States)
  19. CompX, Del Mar, CA (United States)
  20. Univ. of California, Irvine, CA (United States)
  21. National Inst. for Fusion Science, Toki (Japan)
  22. XCEL, Oak Ridge, TN (United States)
  23. Nova Photonics, Princeton, NJ (United States)
  24. Univ. of Colorado, Boulder, CO (United States)
  25. Lehigh Univ., Bethlehem, PA (United States)
Publication Date:
OSTI Identifier:
1256734
Report Number(s):
PPPL--5092
Journal ID: ISSN 0029-5515
Grant/Contract Number:
AC02-09CH11466
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 55; Journal Issue: 10; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY NSTX; spherical torus; overview; toroidal plasmas; transport; simulation; code; disruptions; turbulence; tokamaks; geometry; models