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A study is made of the effect of plasma elongation (κ) on parity of a global electromagnetic (EM) ion temperature gradient mode and intrinsic rotation generation. An odd parity component of the mode is generated by global EM effects and increases with β (=plasma thermal energy/magnetic energy), enhancing the symmetry breaking and subsequent Reynolds stress [Kaang et al., Phys. Plasmas 25, 012505 (2018)]. The plasma elongation is shown to diminish the parity change via the reduction in the effective ion temperature gradient by a factor α = 1 − E ′ , where E = r (κ − 1) / (κ + 1). A quasi-linear analysis indicates that plasma elongation can weaken the generation of intrinsic torque induced by the global EM effect as a result of the decline of the parity change. [ABSTRACT FROM AUTHOR]

A study is conducted on the impact of electromagnetic (EM) fluctuations on residual Reynolds stress in the context of the quasi-linear theory. We employ a fluid formulation describing EM ion temperature gradient turbulence. Analyses show that finite plasma β (=plasma thermal energy/magnetic energy) significantly increases the residual stress, potentially leading to the strong enhancement of flow generation in high β plasmas. We identify that this strong increase of residual stress originates from the reinforcement of radial (kǁ) (=spectrally averaged parallel wavenumber) asymmetry due to the deformation of eigenfunctions near a rational surface. [ABSTRACT FROM AUTHOR]

Parametric instabilities of Alfvén-ion-cyclotron (AIC) waves and the turbulence driven by them are investigated using a particle-in-cell simulation technique. By introducing anisotropic ion temperature, a broad spectrum of AIC wave is excited. In addition to the normal AIC waves, their harmonic modes and upper sideband modes are found. Through the interaction of these Alfvénic waves and longitudinal electrostatic waves, Alfvénic turbulence is developed. Excitation of density and electromagnetic waves and their mode coupling structures are investigated using the ω-k spectrum and bicoherence analysis. It is found that the ion-acoustic wave is excited by the modulational instability, and that the ion density mode with a negative group velocity is excited in the high-k region by the decay instability. In addition, a longitudinal mode whose phase velocity behaves similarly to that of the ion-acoustic mode with a shifted wave number is found. This mode is identified as the second harmonic ion-acoustic wave. The inverse cascade structures of the electromagnetic and density fluctuations exhibit an interesting behavior that the density fluctuation shows a dual spectrum, whereas the electrostatic field Ex shows a single spectrum. [ABSTRACT FROM AUTHOR]

The present paper investigates nonlinear saturation of the relativistic Weibel instability by employing theory and a particle-in-cell simulation technique. It is found that the early phase of the instability is in excellent agreement with linear theory. Qualitative agreement with quasilinear prediction is also found. An analysis based on an alternative magnetic trapping saturation theory reveals that a relativistic formula leads to a substantial discrepancy between theory and simulation. However, excellent agreement is recovered in the nonrelativistic regime. The analysis of the Weibel instability beyond the quasilinear saturation stage reveals an inverse cascade process via a nonlinear decay instability involving electrostatic fluctuation. [ABSTRACT FROM AUTHOR]

We perform a computational study of the effects of finite plasma β(= plasma thermal energy/magnetic energy) on the residual stress in the context of the quasi-linear theory. The five-field electromagnetic (EM) toroidal ion temperature gradient (ITG) model is considered in the realistic tokamak geometry. Analyses show that the residual stress significantly increases and its radial profile changes from a dipolar to a unipolar shape with increasing β. The change in the mode parity is found to be responsible for the enhancement and the profile change of the residual stress driven by the global EM toroidal ITG mode. This finding highlights the importance of the global eigenmode structure in determining the radial profile of the residual stress. [ABSTRACT FROM AUTHOR]

We perform an analytic study of the tertiary instability driven by a strong excitation of zonal flows during high density low to high (LH) mode transition. The drift resistive ballooning mode is assumed to be a dominant edge turbulence driver. The analysis reproduces main qualitative features of early computational results [Rogers and Drake, Phys. Rev. Lett. 81, 4396 (1998); Guzdar et al, Phys. Plasmas 14, 020701 (2007)], as well as new characteristics of the maximum edge density due to the onset of the tertiary instability. An analytical scaling indicates that the density scaling of LH transition power may be determined by the onset condition of the tertiary instability when the operating density approaches to the Greenwald density. [ABSTRACT FROM AUTHOR]

We present that a statistical method known as the complexity–entropy analysis is useful to characterize a state of plasma turbulence and flux in the resonant magnetic perturbation (RMP) edge localized mode (ELM) control experiment. The stochastic pedestal top temperature fluctuation in the RMP ELM suppression phase is distinguished from the chaotic fluctuation in the natural ELM-free phase. It is discussed that the stochastic temperature fluctuation can be originated from the narrow layer of the field penetration on the pedestal top. The forced magnetic island can emit the resonant drift wave of comparable sizes (relatively low-k) in the RMP ELM suppression phase, and it can result in the generation of stochastic higher wavenumber fluctuations coupled to tangled fields around the island. The analysis of the ion saturation current measurement around the major outer striking point on the divertor shows that it also becomes more stochastic as the stronger plasma response to the RMP field is expected. [ABSTRACT FROM AUTHOR]