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Vorticity dynamics, drift wave turbulence, and zonal flows: a look back and a look ahead
Diamond, P H,Hasegawa, A,Mima, K Published jointly by The Institute of Physics and 2011 Plasma physics and controlled fusion Vol.53 No.12
<P>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.</P>
Kaang, Helen H,Ryu, Chang-Mo,Rha, Kicheol,Rhee, Tongnyeol Published jointly by The Institute of Physics and 2012 Plasma physics and controlled fusion Vol.54 No.5
<P>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 E<SUB>x</SUB> shows a single spectrum.</P>
Modeling nonlinear development of Buneman instability with linear dispersion theory
Jain, Neeraj,Umeda, Takayuki,Yoon, Peter H Published jointly by The Institute of Physics and 2011 Plasma physics and controlled fusion Vol.53 No.2
<P>In this paper, spectra in the nonlinear phases of the Buneman instability are described by instantaneous linear dispersion theory. One-dimensional Vlasov simulation of the Buneman instability shows that nonlinear development is characterized by particle trapping in large-amplitude waves. Trapped particles form counter-streaming beam distribution function in velocity space. In addition to the low-frequency Buneman mode, the simulation also shows excitations of high-frequency electron plasma waves as well as wave modes propagating in the direction opposite to the original electron beam. The actual physics of the wave dynamics is very complicated to analyze. However, by employing linear dispersion theory on the basis of instantaneous electron distributions it is possible to relate the generation of waves to the particle distribution. Specifically, it is shown that excitations of various waves are intimately related to the counter-streaming electron beam distribution. The present approach can be a useful diagnostic tool based upon which an intuitive understanding of the complicated nonlinear physics can be attained.</P>
Nonlinear dynamics of shear flows and plasma rotation in a simple laboratory plasma system
Tynan, G R,Diamond, P H,Holland, C,Muller, S H,Xu, M,Yan, Z,Yu, J Published jointly by The Institute of Physics and 2009 Plasma physics and controlled fusion Vol.51 No.12
<P>Nonlinear turbulent-shear flow interactions are directly measured in a cylindrical helicon plasma device and found to lead to the development of an azimuthally symmetric radially sheared azimuthal flow by the action of a turbulent Reynolds stress which transfers kinetic energy into the large-scale shear flow. Radially resolved measurements of the nonlinear kinetic energy transfer show that the flow is driven at the plasma boundary; temporally resolved flow measurements show a penetration of the resulting azimuthal flow into the central plasma region. The results provide an initial qualitatively test of theoretical predictions, and suggest how similar studies might be carried out in confinement devices.</P>
Kim, Doohyun,Han, Hyunsun,Kim, Ki Min,Park, Jong Kyu,Jeon, Young Mu,Na, Yong-Su,Hong, Sang Hee Published jointly by The Institute of Physics and 2010 Plasma physics and controlled fusion Vol.52 No.9
<P>Numerical simulations are carried out to investigate the applicability of resonant magnetic perturbation (RMP) to KSTAR plasmas for a possible control of edge localized mode (ELM) to suppress or mitigate its damages to divertor materials. For the verification of the feasibility of RMP application, magnetic island configurations, resonant normal fields, magnetic island widths and Chirikov parameters are calculated for two types of KSTAR operation scenarios: steady state and hybrid. Field error correction (FEC) coils in KSTAR are considered to produce externally perturbed magnetic fields for RMP, and the directions of coil currents determine the toroidal mode <I>n</I> and the parity (even or odd). The RMP configurations are described by vacuum superposition of the equilibrium magnetic fields and the perturbed ones induced by FEC coils. The numerical simulations for <I>n</I> = 2 toroidal mode in both operation scenarios show that when the pitches of the equilibrium and perturbed magnetic fields are well aligned, magnetic islands are formed for a series of <I>m</I> poloidal modes and the adjacent islands are overlapped to generate a stochastic layer in the edge region. Even parity turns out to be more effective in making the magnetic islands overlapped to become stochastic field lines in the steady-state operation, while odd parity in the hybrid operation. The formation of the stochastic layer is verified by the calculated Chirikov parameters, which also give basic information on the current requirement of FEC coils. Additionally, lobe structures of stochastic field lines are found in the edge region extended to the divertor plate in the hybrid scenario. Based on the standard vacuum criteria for RMP, the simulation results indicate that the FEC coils will be feasible for control of ELMs and mitigation of divertor heat load by RMP in both steady-state and hybrid operation scenarios.</P>
Shell models and the possibility of application to fusion plasmas
Gü,rcan, Ö,D,Hennequin, P,Vermare, L,Garbet, X,Diamond, P H Published jointly by The Institute of Physics and 2010 Plasma physics and controlled fusion Vol.52 No.4
<P>An extensive study of spectral shell models with possibilities for application to fusion plasmas is discussed. A set of shell models addressing various aspects of the characteristics of fusion plasmas have been derived. Difficulties associated with plasma medium, namely its intrinsic excitability, and importance of mescals have been discussed. The numerical implementation of shell models is discussed. It was observed that depending on the parameter regime, they may lead to steady state or display characteristics of predator–prey dynamics.</P>
Ki, Dae-Han,Jung, Young-Dae Published jointly by The Institute of Physics and 2010 Plasma physics and controlled fusion Vol.52 No.5
<P>The non-thermal effects on the soft-photon transition bremsstrahlung radiation due to the interaction between the electron and the polarized Debye sphere are investigated in generalized Lorentzian plasmas. The impact parameter method with the effective interaction potential taking into account the non-thermal character is applied to obtain the bremsstrahlung radiation cross section as a function of the impact parameter, Debye length, photon energy, projectile energy and spectral index of the generalized Lorentzian plasma. It is shown that the non-thermal effects enhance the maximum value of the bremsstrahlung radiation cross section. It is also found that the non-thermal effects increase the bremsstrahlung radiation cross section. In addition, it is shown that the non-thermal effect on the bremsstrahlung radiation cross section decreases with increasing Debye length.</P>
Plasmon and spin interference effects on electron collisions in hot quantum plasmas
Jung, Young-Dae,Kato, Daiji Published jointly by The Institute of Physics and 2009 Plasma physics and controlled fusion Vol.51 No.6
<P>The effects of plasmon and spin interference in electron–electron collisions are investigated in hot quantum plasmas. It is shown that the plasmon effect suppresses the electron–electron collision cross section for 0 < β(≡ℏω<SUB>0</SUB>/<I>k</I><SUB>B</SUB><I>T</I>) < 0.8 but, enhances the cross section for 0.8 < β < 1, where ω<SUB>0</SUB> is the plasma frequency and <I>T</I> is the plasma temperature. In addition, it is shown that the spin interference effect strongly suppresses the collision cross section and is more significant near the scattering angle &thetas;<SUB>L</SUB> = π/4.</P>
Hong, Suk-Ho,Grisolia, Christian,Monier-Garbet, Pascale Published jointly by The Institute of Physics and 2009 Plasma physics and controlled fusion Vol.51 No.7
<P>In-vessel dusts will be an important issue in next generation fusion devices. They affect not only plasma operations but also safety limits. A new image processing technique for in-vessel dust research is developed in Tore Supra (TS). This paper describes the image processing technique for in-vessel dust study based on simple standard image processing techniques. The technique is intended to use visible standard RGB CCD cameras at a standard frame rate already installed in TS. Studying the traces of straight line-like dust trajectories appearing in the CCD images during the plasma shots, the temporal evolution and the spatial locations of dust creation events (DCEs) can be monitored. Building a database of DCEs, information on the short/long term behavior of in-vessel dusts are obtained. Analyzing the database, statistics on DCEs can be found. Finally, DCEs during 22 ohmic discharges in 2006 CIMES campaign in TS are illustrated as an example.</P>
Control of plasma profiles in DIII-D discharges
Gohil, P,Evans, T E,Ferron, J R,Moyer, R A,Petty, C C,Burrell, K H,Casper, T A,Garofalo, A M,Hyatt, A W,Jayakumar, R J,Kessel, C,Kim, J Y,La Haye, R J,Lohr, J,Luce, T C,Makowski, M A,Mazon, D,Menard, Published jointly by The Institute of Physics and 2006 Plasma physics and controlled fusion Vol.48 No.a5
<P>Active control of plasma profiles is an essential requirement for operating within plasma stability limits, for steady-state operation and for optimization of the plasma performance. In DIII-D, plasma profiles have been actively controlled using various actuators in the following manner: (a) real time closed loop control of the <I>q</I> profile evolution using electron cyclotron heating and neutral beam injection as actuators; (b) active control of the density and pressure profiles in quiescent H-mode and quiescent double barrier plasmas using electron cyclotron current drive (ECCD) and pellet injection; (c) active control of the edge profiles to suppress edge localized modes using resonant magnetic perturbation with toroidal mode number <I>n</I> = 3, (d) real time control of the current density profile to suppress neoclassical tearing modes using localized deposition of co-ECCD.</P>