Simulation of microtearing turbulence in national spherical torus experiment

Journal Article · Tue May 15 04:00:00 EDT 2012 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.3694104· OSTI ID:22072397

Guttenfelder, W; Kaye, S M; Bell, R E; Hammett, G W; LeBlanc, B P; Mikkelsen, D R; Ren, Y ^[1]; Candy, J ^[2]; Nevins, W M; Wang, E ^[3]; Zhang, J; Crocker, N A ^[4]; Yuh, H ^[5]

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1. Princeton Plasma Physics Laboratory, Princeton New Jersey 08543 (United States)
2. General Atomics, San Diego, California 92186 (United States)
3. Lawrence Livermore National Laboratory, Livermore, California 04551 (United States)
4. University of California Los Angeles, California 90095 (United States)
5. Nova Photonics Inc., Princeton, New Jersey 08540 (United States)

Thermal energy confinement times in National Spherical Torus Experiment (NSTX) dimensionless parameter scans increase with decreasing collisionality. While ion thermal transport is neoclassical, the source of anomalous electron thermal transport in these discharges remains unclear, leading to considerable uncertainty when extrapolating to future spherical tokamak (ST) devices at much lower collisionality. Linear gyrokinetic simulations find microtearing modes to be unstable in high collisionality discharges. First non-linear gyrokinetic simulations of microtearing turbulence in NSTX show they can yield experimental levels of transport. Magnetic flutter is responsible for almost all the transport ({approx}98%), perturbed field line trajectories are globally stochastic, and a test particle stochastic transport model agrees to within 25% of the simulated transport. Most significantly, microtearing transport is predicted to increase with electron collisionality, consistent with the observed NSTX confinement scaling. While this suggests microtearing modes may be the source of electron thermal transport, the predictions are also very sensitive to electron temperature gradient, indicating the scaling of the instability threshold is important. In addition, microtearing turbulence is susceptible to suppression via sheared E Multiplication-Sign B flows as experimental values of E Multiplication-Sign B shear (comparable to the linear growth rates) dramatically reduce the transport below experimental values. Refinements in numerical resolution and physics model assumptions are expected to minimize the apparent discrepancy. In cases where the predicted transport is strong, calculations suggest that a proposed polarimetry diagnostic may be sensitive to the magnetic perturbations associated with the unique structure of microtearing turbulence.

• OSTI ID: 22072397
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 5 Vol. 19; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
CONFINEMENT
DISTURBANCES
ELECTRON TEMPERATURE
ELECTRONS
IONS
NEOCLASSICAL TRANSPORT THEORY
NONLINEAR PROBLEMS
NSTX DEVICE
PLASMA SIMULATION
POLARIMETRY
SCALING
SHEAR
STOCHASTIC PROCESSES
TEMPERATURE GRADIENTS
TEST PARTICLES
TURBULENCE