Access to sustained high-beta with internal transport barrier and negative central magnetic shear in DIII-D

Journal Article · Sun Jan 01 00:00:00 EST 2006 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2185010· OSTI ID:1170841

Garofalo, A. M. ^[1]; Doyle, E. J. ^[2]; Ferron, J. R. ^[3]; Greenfield, C. M. ^[3]; Groebner, R. J. ^[3]; Hyatt, A. W. ^[3]; Jackson, G. L. ^[3]; Jayakumar, R. J. ^[4]; Kinsey, J. E. ^[5]; La Haye, R. J. ^[3]; McKee, G. R. ^[6]; Murakami, M. ^[7]; Okabayashi, M. ^[8]; Osborne, T. H. ^[3]; Petty, C. C. ^[3]; Politzer, P. A. ^[3]; Reimerdes, H. ^[1]; Scoville, J. T. ^[3]; Solomon, W. M. ^[8]; St. John, H. E. ^[3] ; Strait, E. J. ^[3]; Turnbull, A. D. ^[3]; Wade, M. R. ^[3]; VanZeeland, M. A. ^[9]

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1. Columbia Univ., New York, NY (United States)
2. Univ. of California, Los Angeles, CA (United States)
3. General Atomics, San Diego, CA (United States)
4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
5. Lehigh Univ., Bethlehem, PA (United States)
6. Univ. of Wisconsin, Madison, WI (United States)
7. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
8. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
9. Oak Ridge Inst. for Science and Education (ORISE), Oak Ridge, TN (United States)

High values of normalized β (β_N~4) and safety factor (q_min~2) have been sustained simultaneously for ~2 s in DIII-D [J.L. Luxon, Nucl. Fusion 42, 64 (2002)], suggesting a possible path to high fusion performance, steady-state tokamak scenarios with a large fraction of bootstrap current. The combination of internal transport barrier and negative central magnetic shear at high β results in high confinement (H_89P>2.5) and large bootstrap current fraction (f_BS>60%) with good alignment. Previously, stability limits in plasmas with core transport barriers have been observed at moderate values of β_N (<3) because of the pressure peaking which normally develops from improved core confinement. In recent DIII-D experiments, the internal transport barrier is clearly observed in the electron density and in the ion temperature and rotation profiles at ρ~0.5 but not in the electron temperature profile, which is very broad. The misalignment of Ti and Te gradients may help to avoid a large local pressure gradient. Furthermore, at low internal inductance ~0.6, the current density gradients are close to the vessel and the ideal kink modes are strongly wall-coupled. Simultaneous feedback control of both external and internal sets of n=1 magnetic coils was used to maintain optimal error field correction and resistive wall mode stabilization, allowing operation above the free-boundary β limit. Largree-boundary β limit. Large particle orbits at high safety factor in the core help to broaden both the pressure and the beam-driven current profiles, favorable for steady-state operation. At plasma current flat top and β~5%, a noninductive current fraction of ~100% has been observed. Stability modeling shows the possibility for operation up to the ideal-wall limit at β~6%

• Sponsoring Organization: USDOE
• DOE Contract Number: FG02-89ER53297; FG03-01ER54615; AC02-04ER54698; W-7405-ENG-48; AC02-76CH03073; AC05-00OR22725
• OSTI ID: 1170841
• Journal Information: Physics of Plasmas, Vol. 13, Issue 5; ISSN 1070-664X: PHPAEN
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY