Center for Fusion Theory

Daejeon, South Korea

Center for Fusion Theory

Daejeon, South Korea

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Malkov M.A.,University of California at San Diego | Malkov M.A.,Kavli Institute for Particle Astrophysics and Cosmology | Diamond P.H.,University of California at San Diego | Diamond P.H.,Center for Fusion Theory | And 4 more authors.
Astrophysical Journal | Year: 2013

Supernova remnants (SNRs), as the major contributors to the galactic cosmic rays (CRs), are believed to maintain an average CR spectrum by diffusive shock acceleration regardless of the way they release CRs into the interstellar medium (ISM). However, the interaction of the CRs with nearby gas clouds crucially depends on the release mechanism. We call into question two aspects of a popular paradigm of the CR injection into the ISM, according to which they passively and isotropically diffuse in the prescribed magnetic fluctuations as test particles. First, we treat the escaping CR and the Alfvén waves excited by them on an equal footing. Second, we adopt field-aligned CR escape outside the source, where the waves become weak. An exact analytic self-similar solution for a CR "cloud" released by a dimmed accelerator strongly deviates from the test-particle result. The normalized CR partial pressure may be approximated as , where p is the momentum of CR particle, and z is directed along the field. The core of the cloud expands as and decays in time as . The diffusion coefficient D NL is strongly suppressed compared to its background ISM value D ISM: D NL ∼ D ISMexp (- Π) ≪ D ISM for sufficiently high field-line-integrated CR partial pressure, Π. When Π ≫ 1, the CRs drive Alfvén waves efficiently enough to build a transport barrier ( - "pedestal") that strongly reduces the leakage. The solution has a spectral break at p = p br, where p br satisfies the equation D NL (p br) ≃ z 2/t. © 2013. The American Astronomical Society. All rights reserved.


Wang L.,Huazhong University of Science and Technology | Wang L.,Center for Fusion Theory | Diamond P.H.,Center for Fusion Theory | Diamond P.H.,University of California at San Diego
Physical Review Letters | Year: 2013

A mechanism for turbulent acceleration of parallel rotation is discovered using gyrokinetic theory. This new turbulent acceleration term cannot be written as a divergence of parallel Reynolds stress. Therefore, turbulent acceleration acts as a local source or sink of parallel rotation. The physics of turbulent acceleration is intrinsically different from the Reynolds stress. For symmetry breaking by positive intensity gradient, a positive turbulent acceleration, i.e., cocurrent rotation, is predicted. The turbulent acceleration is independent of mean rotation and mean rotation gradient, and so constitutes a new candidate for the origin of spontaneous rotation. A quasilinear estimate for ion temperature gradient turbulence shows that the turbulent acceleration of parallel rotation is explicitly linked to the ion temperature gradient scale length and temperature ratio Ti0/Te0. Methods for testing the effects of turbulent parallel acceleration by gyrokinetic simulation and experiment are proposed. © 2013 American Physical Society.


Leconte M.,Center for Fusion Theory | Diamond P.H.,Center for Fusion Theory | Diamond P.H.,University of California at San Diego
Physics of Plasmas | Year: 2011

Recent experiments showed a decrease of long range correlations during the application of resonant magnetic perturbations (RMPs) Y. Xu, Nucl. Fusion 51, 063020 (2011). This finding suggests that RMPs damp zonal flows. To elucidate the effect of the RMPs on zonal structures in drift wave turbulence, we construct a generalized Hasegawa-Wakatani model including RMP fields. The effect of the RMPs is to induce a linear coupling between the zonal electric field and the zonal density gradient, which drives the system to a state of electron radial force balance for large RMP amplitude. A predator-prey model coupling the primary drift wave dynamics to the zonal modes evolution is derived. This model has both turbulence drive and RMP amplitude as control parameters and predicts a novel type of transport bifurcation in the presence of RMPs. The novel regime has a power threshold which increases with RMP amplitude as c ∼ [ B r B] 2. © 2011 American Institute of Physics.


Leconte M.,Center for Fusion Theory | Diamond P.H.,Center for Fusion Theory | Diamond P.H.,University of California at San Diego | Xu Y.,EURATOM
Nuclear Fusion | Year: 2014

We study the effects of resonant magnetic perturbations (RMPs) on turbulence, flows and confinement in the framework of resistive drift-wave turbulence. This work was motivated, in parts, by experiments reported at the IAEA 2010 conference (Xu et al 2011 Nucl. Fusion 51 062030) which showed a decrease of long-range correlations during the application of RMPs. We derive and apply a zero-dimensional predator-prey model coupling the drift-wave-zonal-mode system (Leconte and Diamond 2012 Phys. Plasmas 19 055903) to the evolution of mean quantities. This model has both density-gradient drive and RMP amplitude as control parameters and predicts a novel type of transport bifurcation in the presence of RMPs. This model allows a description of the full L-H transition evolution with RMPs, including the mean sheared flow evolution. The key results are the following: (i) the L-I and I-H power thresholds both increase with RMP amplitude |b̃x|, the relative increase of the L-I threshold scales as ΔPLI ∞ |b̃x| 2ν * -2 ρs -2, where ν* is edge collisionality and ρs is the sound gyroradius. (ii) RMPs are predicted to decrease the hysteresis between the forward and back-transition. (iii) Taking into account the mean density evolution, the density profile - sustained by the particle source - has an increased turbulent diffusion compared with the reference case without RMPs which provides one possible explanation for the density pump-out effect. © 2014 IAEA, Vienna.


Leconte M.,Center for Fusion Theory | Diamond P.H.,Center for Fusion Theory | Diamond P.H.,University of California at San Diego
Physics of Plasmas | Year: 2012

In this work, we study the effects of resonant magnetic perturbations (RMPs) on turbulence, flows, and confinement in the framework of resistive drift wave turbulence. We extend the Hasegawa-Wakatani model to include RMP fields. The effect of the RMPs is to induce a linear coupling between the zonal electric field and the zonal density gradient, which drives the system to a state of electron radial force balance for large δBr/B0. Both the vorticity flux (Reynolds stress) and particle flux are modulated. We derive an extended predator prey model which couples zonal potential and density dynamics to the evolution of turbulence intensity. This model has both turbulence drive and RMP amplitude as control parameters and predicts a novel type of transport bifurcation in the presence of RMPs. We find states that are similar to the ZF-dominated state of the standard predator-prey model, but for which the power threshold is now a function of the RMP strength. For small RMP amplitude, the energy of zonal flows decreases and the turbulence energy increases with δBr/B0, corresponding to a damping of zonal flows. © 2012 American Institute of Physics.


Diamond P.H.,Center for Fusion Theory | Diamond P.H.,University of California at San Diego | Hasegawa A.,Osaka University | Mima K.,Osaka University
Plasma Physics and Controlled Fusion | Year: 2011

This paper surveys the basic ideas and results on fundamental models of drift wave turbulence, the formation of zonal flows, shear suppression of turbulence and transport, coupled drift wave and zonal flow dynamics and application to transport bifurcations and transitions. Application to vortex dynamics and zonal flow phenomena in EMHD systems are discussed, as well. These are relevant to aspects of ICF and laser plasma physics. Throughout, an effort is made to focus on fundamental physics ideas. © 2011 IOP Publishing Ltd.


Lesur M.,Center for Fusion Theory | Lesur M.,Kyushu University | Diamond P.H.,Center for Fusion Theory | Diamond P.H.,University of California at San Diego
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2013

In the presence of wave dissipation, phase-space structures emerge in nonlinear Vlasov dynamics. Our theory gives a simple relation between the growth of these coherent structures and that of the wave energy. The structures can drive the wave by direct momentum exchange, which explains the existence of nonlinear instabilities in both barely unstable and linearly stable (subcritical) regimes. When dissipation is modeled by a linear term in the field equation, simple expressions of a single-hole growth rate and of the initial perturbation threshold are in agreement with numerical simulations. © 2013 American Physical Society.


Gurcan O.D.,Ecole Polytechnique - Palaiseau | Diamond P.H.,Center for Fusion Theory
Journal of Physics A: Mathematical and Theoretical | Year: 2015

The general aspects of zonal flow physics, their formation, damping and interplay with quasi two dimensional turbulence are explained in the context of magnetized plasmas and quasi-geostrophic fluids with an emphasis on formation and selection of spatial patterns. General features of zonal flows as they appear in planetary atmospheres, rotating convection experiments and fusion plasmas are reviewed. Detailed mechanisms for excitation and damping of zonal flows, and their effect on turbulence via shear decorrelation is discussed. Recent results on nonlocality and staircase formation are outlined. © 2015 IOP Publishing Ltd.


Guo Z.B.,Center for Fusion Theory | Diamond P.H.,Center for Fusion Theory | Diamond P.H.,University of California at San Diego
Physical Review Letters | Year: 2015

We demonstrate that E×B shear, VE×B′, governs the dynamics of the cross phase of the peeling-ballooning-(PB-)mode-driven heat flux, and so determines the evolution from the edge-localized (ELMy) H mode to the quiescent (Q) H mode. A physics-based scaling of the critical E×B shearing rate (VE×B,cr′) for accessing the QH mode is predicted. The ELMy H mode to the QH-mode evolution is shown to follow from the conversion from a phase locked state to a phase slip state. In the phase locked state, PB modes are pumped continuously, so bursts occur. In the slip state, the PB activity is a coherent oscillation. Stronger E×B shearing implies a higher phase slip frequency. This finding predicts a new state of cross phase dynamics and shows a new way to understand the physics mechanism for ELMy to the QH-mode evolution. © 2015 American Physical Society.


Guo Z.B.,Center for Fusion Theory | Diamond P.H.,Center for Fusion Theory | Diamond P.H.,University of California at San Diego | Kosuga Y.,Kyushu University | Gurcan O.D.,Ecole Polytechnique - Palaiseau
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

We present a theory of turbulent elasticity, a property of drift-wave-zonal-flow (DW-ZF) turbulence, which follows from the time delay in the response of DWs to ZF shears. An emergent dimensionless parameter |〈v〉|/Δωk is found to be a measure of the degree of Fickian flux-gradient relation breaking, where |〈v〉| is the ZF shearing rate and Δωk is the turbulence decorrelation rate. For |〈v〉|/Δωk>1, we show that the ZF evolution equation is converted from a diffusion equation, usually assumed, to a telegraph equation, i.e., the turbulent momentum transport changes from a diffusive process to wavelike propagation. This scenario corresponds to a state very close to the marginal instability of the DW-ZF system, e.g., the Dimits shift regime. The frequency of the ZF wave is ΩZF=±γd1/2γmodu1/2, where γd is the ZF friction coefficient and γmodu is the net ZF growth rate for the case of the Fickian flux-gradient relation. This insight provides a natural framework for understanding temporally periodic ZF structures in the Dimits shift regime and in the transition from low confined mode to high confined mode in confined plasmas. © 2014 American Physical Society.

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