Production and stability of high-beta DIII-D discharges with reversed magnetic shear
- Columbia Univ., New York, NY (United States). Dept. of Applied Physics
- Lawrence Livermore National Lab., CA (United States)
- General Atomics, San Diego, CA (United States); and others
Plasma configurations with reversed magnetic shear have been proposed for steady-state tokamak operation since the plasma profiles can be made consistent with good confinement, high bootstrap current fraction, and stability at very high beta. The stability of reversed magnetic shear discharges with beta up to 11% has previously been demonstrated in DIII-D. Reversed magnetic shear (RMS) refers to a safety factor profile, q({rho}), which is a non-monotonic function of minor radius, {rho}. The magnetic shear S {equivalent_to} ({rho}/q) dq/d{rho} is negative within the plasma core and positive at the edge. When S < 0, short wavelength ballooning modes are stable, and the toroidal current density peaks near the radius of minimum safety factor, q{sub min}. This off-axis current maximum can be aligned, with the non-inductive bootstrap current generated by the pressure gradient, reducing the requirements for external current drive. Stabilization of long wavelength external kink modes at high beta requires a nearby conducting wall, and this effect has been demonstrated in DIII-D experiments. In this paper, the authors describe high confinement and high beta DIII-D discharges having strongly reversed magnetic shear. These discharges differ from previously reported RMS plasmas since high-quality measurements of the internal magnetic field now permit clear documentation of the central shear reversal region in high beta plasmas with enhanced confinement. Additionally, these RMS discharges are produced in DIII-D with power plant-relevant ion temperatures T{sub i}(0) up to 20 keV, at Troyon-normalized beta up to 4, high central safety factor with q(0) often exceeding 10 while q{sub min} {approximately} 2, and with or without the improved edge confinement characteristic of H-mode operation.
- Research Organization:
- General Atomics, San Diego, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Columbia Univ., New York, NY (United States). Dept. of Applied Physics; Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC03-89ER51114; AC05-84OR21400; FG02-89ER53297; W-7405-ENG-48
- OSTI ID:
- 195739
- Report Number(s):
- GA-A22101; CONF-950704-18; ON: DE96005591; TRN: AHC29605%%115
- Resource Relation:
- Conference: 22. European conference on controlled fusion and plasma physics, Bournemouth (United Kingdom), 2-7 Jul 1995; Other Information: PBD: Jul 1995
- Country of Publication:
- United States
- Language:
- English
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