skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Improved confinement in highly powered high performance scenarios on DIII-D

Abstract

DIII-D has recently demonstrated improved energy confinement by injecting neutral deuterium gas into high performance near-double null divertor (DND) plasmas during high power operation. Representative parameters for these plasmas are: q 95 = 6, P IN up to 15 MW, H 98 = 1.4–1.8, and β N = 2.5–4.0. The ion B x $$\triangledown$$B direction is away from the primary X-point. While plasma conditions at lower to moderate power input (e.g., 11 MW) are shown to be favorable to successful puff-and-pump radiating divertor applications, particularly when using argon seeds, plasma behavior at higher powers (e.g., ≥14 MW) may make successful puff-and-pump operation more problematic. In contrast to lower powered high performance plasmas, both $$\tau$$ E and β N in the high power cases (≥14 MW) increased and ELM frequency decreased, as density was raised by deuterium gas injection. Improved performance in the higher power plasmas was tied to higher pedestal pressure, which according to peeling-ballooning mode stability analysis using the ELITE code could increase with density along the kink/peeling stability threshold, while the pedestal pressure gradient in the lower power discharges were limited by the ballooning threshold. This resulted in improved fueling efficiency and ≈10% higher $$\tau$$ E and β N than is normally observed in comparable high performance plasmas on DIII-D. Applying the puff-and-pump radiating divertor approach at moderate versus high power input is shown to result in a much different evolution in core and pedestal plasma behavior. In conclusion, we find that injecting deuterium gas into these highly powered DND plasmas may open up a new avenue for achieving elevated plasma performance, including better fueling, but the resulting higher density may also complicate application of a radiating divertor approach to heat flux reduction in present-day tokamaks, if scenarios involving second-harmonic electron cyclotron heating are used.

Authors:
 [1];  [1];  [2];  [1];  [1];  [3];  [2];  [2];  [1];  [1];  [2];  [4];  [1];  [2];  [5]
  1. General Atomics, San Diego, CA (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  4. Columbia Univ., New York, NY (United States)
  5. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1371544
Grant/Contract Number:
FC02-04ER54698; AC52-07NA27344; FG02-04ER54761; AC04-94AL85000
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 8; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Petrie, Thomas W., Osborne, Thomas, Fenstermacher, Max E., Ferron, John R., Groebner, Richard J., Grierson, Brian, Holcomb, Christopher T., Lasnier, C., Leonard, Anthony W., Luce, Timothy C., Makowski, Michael A., Turco, Francesca, Solomon, Wayne M., Victor, Brian S., and Watkins, Jonathan G. Improved confinement in highly powered high performance scenarios on DIII-D. United States: N. p., 2017. Web. doi:10.1088/1741-4326/aa7399.
Petrie, Thomas W., Osborne, Thomas, Fenstermacher, Max E., Ferron, John R., Groebner, Richard J., Grierson, Brian, Holcomb, Christopher T., Lasnier, C., Leonard, Anthony W., Luce, Timothy C., Makowski, Michael A., Turco, Francesca, Solomon, Wayne M., Victor, Brian S., & Watkins, Jonathan G. Improved confinement in highly powered high performance scenarios on DIII-D. United States. doi:10.1088/1741-4326/aa7399.
Petrie, Thomas W., Osborne, Thomas, Fenstermacher, Max E., Ferron, John R., Groebner, Richard J., Grierson, Brian, Holcomb, Christopher T., Lasnier, C., Leonard, Anthony W., Luce, Timothy C., Makowski, Michael A., Turco, Francesca, Solomon, Wayne M., Victor, Brian S., and Watkins, Jonathan G. Fri . "Improved confinement in highly powered high performance scenarios on DIII-D". United States. doi:10.1088/1741-4326/aa7399.
@article{osti_1371544,
title = {Improved confinement in highly powered high performance scenarios on DIII-D},
author = {Petrie, Thomas W. and Osborne, Thomas and Fenstermacher, Max E. and Ferron, John R. and Groebner, Richard J. and Grierson, Brian and Holcomb, Christopher T. and Lasnier, C. and Leonard, Anthony W. and Luce, Timothy C. and Makowski, Michael A. and Turco, Francesca and Solomon, Wayne M. and Victor, Brian S. and Watkins, Jonathan G.},
abstractNote = {DIII-D has recently demonstrated improved energy confinement by injecting neutral deuterium gas into high performance near-double null divertor (DND) plasmas during high power operation. Representative parameters for these plasmas are: q95 = 6, PIN up to 15 MW, H98 = 1.4–1.8, and βN = 2.5–4.0. The ion B x $\triangledown$B direction is away from the primary X-point. While plasma conditions at lower to moderate power input (e.g., 11 MW) are shown to be favorable to successful puff-and-pump radiating divertor applications, particularly when using argon seeds, plasma behavior at higher powers (e.g., ≥14 MW) may make successful puff-and-pump operation more problematic. In contrast to lower powered high performance plasmas, both $\tau$E and βN in the high power cases (≥14 MW) increased and ELM frequency decreased, as density was raised by deuterium gas injection. Improved performance in the higher power plasmas was tied to higher pedestal pressure, which according to peeling-ballooning mode stability analysis using the ELITE code could increase with density along the kink/peeling stability threshold, while the pedestal pressure gradient in the lower power discharges were limited by the ballooning threshold. This resulted in improved fueling efficiency and ≈10% higher $\tau$E and βN than is normally observed in comparable high performance plasmas on DIII-D. Applying the puff-and-pump radiating divertor approach at moderate versus high power input is shown to result in a much different evolution in core and pedestal plasma behavior. In conclusion, we find that injecting deuterium gas into these highly powered DND plasmas may open up a new avenue for achieving elevated plasma performance, including better fueling, but the resulting higher density may also complicate application of a radiating divertor approach to heat flux reduction in present-day tokamaks, if scenarios involving second-harmonic electron cyclotron heating are used.},
doi = {10.1088/1741-4326/aa7399},
journal = {Nuclear Fusion},
number = 8,
volume = 57,
place = {United States},
year = {Fri Jun 09 00:00:00 EDT 2017},
month = {Fri Jun 09 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on June 9, 2018
Publisher's Version of Record

Save / Share:
  • Here, impurity transport in the DIII-D tokamak is investigated in stationary high confinement (H-mode) regimes without edge localized modes (ELMs). In plasmas maintained by resonant magnetic perturbation (RMP) ELM-suppression and QH-mode the confinement time of fluorine (Z=9) is equivalent to that in ELMing discharges with 40 Hz ELMs. For selected discharges with impurity injection the impurity particle confinement time compared to the energy confinement time is in the range of τ pe ≈ 2 $-$ 3. In QH-mode operation the impurity confinement time is shown to be smaller for intense, coherent magnetic and density fluctuations of the edge harmonicmore » oscillation than weaker fluctuations. Transport coefficients are derived from the time evolution of the impurity density profile and compared to neoclassical and turbulent transport models NEO and TGLF. Neoclassical transport of fluorine is found to be small compared to the experimental values. In the ELMing and RMP ELM-suppressed plasma the impurity transport is affected by the presence of tearing modes. For radii larger than the mode radius the TGLF diffusion coefficient is smaller than the experimental value by a factor of 2-3, while the convective velocity is within error estimates. Low levels of diffusion are observed for radii smaller than the tearing mode radius. In the QH-mode plasma investigated, the TGLF diffusion coefficient higher inside of ρ = 0.4 and lower outside of 0.4 than the experiment, and the TGLF convective velocity is more negative by a factor of approximately 1.7.« less
  • The first observation of a high-confinement mode with reduced energy transport in both the center and the edge induced by the injection of neon impurities is reported in this paper. This improved high mode develops from an improved low-confinement mode. Linear growth rate calculations indicate that a new theoretical mechanism, the stabilization of high wave number drift waves by impurities, is at work, combined with {bold E}{times}{bold B} velocity shear suppression of low wave number instabilities. {copyright} {ital 1999} {ital The American Physical Society}
  • High confinement mode ([ital H]-mode) discharges with peaked toroidal current density profile (high internal inductance, [ital l][sub [ital i]]) and improved confinement are obtained in the DIII-D tokamak by dynamically varying the current profile using a rapid elongation ramp technique. The confinement improvement increases with [ital l][sub [ital i]] and persists in the presence of edge-localized modes. The plasma toroidal rotation and the corresponding radial electric field component also increase with the peakedness of the current density profile.
  • Here, recent experiments in DIII-D have led to the discovery of a means of modifying edge turbulence to achieve stationary, high confinement operation without Edge Localized Mode (ELM) instabilities and with no net external torque input. Eliminating the ELM-induced heat bursts and controlling plasma stability at low rotation represent two of the great challenges for fusion energy. By exploiting edge turbulence in a novel manner, we achieved excellent tokamak performance, well above the H 98y2 international tokamak energy confinement scaling (H 98y2=1.25), thus meeting an additional confinement challenge that is usually difficult at low torque. The new regime is triggeredmore » in double null plasmas by ramping the injected torque to zero and then maintaining it there. This lowers ExB rotation shear in the plasma edge, allowing low-k, broadband, electromagnetic turbulence to increase. In the H-mode edge, a narrow transport barrier usually grows until MHD instability (a peeling ballooning mode) leads to the ELM heat burst. However, the increased turbulence reduces the pressure gradient, allowing the development of a broader and thus higher transport barrier. A 60% increase in pedestal pressure and 40% increase in energy confinement result. An increase in the ExB shearing rate inside of the edge pedestal is a key factor in the confinement increase. Strong double-null plasma shaping raises the threshold for the ELM instability, allowing the plasma to reach a transport-limited state near but below the explosive ELM stability boundary. The resulting plasmas have burning-plasma-relevant β N=1.6-1.8 and run without the need for extra torque from 3D magnetic fields. To date, stationary conditions have been produced for 2 s or 12 energy confinement times, limited only by external hardware constraints. Stationary operation with improved pedestal conditions is highly significant for future burning plasma devices, since operation without ELMs at low rotation and good confinement is key for fusion energy production.« less
  • A new, long-lived limit cycle oscillation (LCO) regime has been observed in the edge of near zero torque high-performance DIII-D tokamak plasma discharges. These LCOs are localized and comprised of density turbulence, gradient drives, and E X B velocity shear damping ( E and B are the local radial electric and total magnetic fields). Density turbulence sequentially acts as a predator (via turbulence transport) of profile gradients and a prey (via shear suppression) to the E X B velocity shear. Reported here for the first time, a unique spatiotemporal variation of the local E X B velocity which is foundmore » to be essential for the existence of this system. The LCO system is quasi-stationary, existing from 3 to 12 plasma energy confinement times (~30 to 900 LCO cycles) limited by hardware constraints. In conclusion, this plasma system appears to contribute strongly to the edge transport in these high-performance and transient-free plasmas as evident from oscillations in transport relevant edge parameters at LCO timescale.« less