| 1. |
- Fransson, Emil, 1986, et al.
(författare)
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Upgrade and benchmark of quasi-linear transport model EDWM
- 2022
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 29:11
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Tidskriftsartikel (refereegranskat)abstract
- The verification of a new saturation rule applied to the quasi-linear fluid model EDWM (extended drift wave model) and the calibration of several other features are presented. As one of the computationally fastest first-principle-based core transport models, EDWM can include an arbitrary number of ions and charge states. This feature is especially important for experimental devices with plasma-facing components made of heavy elements, such as the upcoming ITER device. As a quasi-linear model, EDWM solves a linear dispersion relation to obtain the instabilities driving the turbulence and combines the linear description with an estimation of the saturation level of the electrostatic potential to determine the fluxes. A new saturation rule at the characteristic length combined with a spectral filter for the poloidal wavenumber dependency is developed. The shape of the filter has been fitted against the poloidal wavenumber dependency of the electrostatic potential from non-linear gyrokinetic simulations. Additionally, EDWM's collision frequency and safety factor dependencies, as well as the electron heat flux level, have been calibrated against gyrokinetic and gyrofluid results. Finally, the saturation level has been normalized against non-linear gyrokinetic simulations and later validated against experimental measured fluxes from 12 discharges at JET.
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| 2. |
- Weiland, Jan, 1944, et al.
(författare)
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Toroidal drift modes driven by the magnetic drift resonances
- 2018
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 25:9
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Tidskriftsartikel (refereegranskat)abstract
- Here, we find that the kinetic and fluid linear drift resonances have several similarities. The reason for our interest in this is that our fluid model has recently been shown to be exact for drift waves and other modes in that frequency range. Thus, transport is driven by the fluid linear growth rate and our drift wave system behaves like a cold beam-plasma system although it has a finite temperature. A main similarity is that neither fluid nor kinetic responses should be expanded in the curvature in the bulk interior of tokamaks. That we can use the fluid response close to the magnetic drift resonance is a consequence of the fact that the closure is exact. A systematic orbit integration technique is introduced for deriving the fluid model and evaluating the effects of nonlinearities.
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| 3. |
- Brodrick, J. P., et al.
(författare)
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Testing nonlocal models of electron thermal conduction for magnetic and inertial confinement fusion applications
- 2017
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 24:9
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Tidskriftsartikel (refereegranskat)abstract
- Three models for nonlocal electron thermal transport are here compared against Vlasov-Fokker-Planck (VFP) codes to assess their accuracy in situations relevant to both inertial fusion hohlraums and tokamak scrape-off layers. The models tested are (i) a moment-based approach using an eigenvector integral closure (EIC) originally developed by Ji, Held, and Sovinec [Phys. Plasmas 16, 022312 (2009)]; (ii) the non-Fourier Landau-fluid (NFLF) model of Dimits, Joseph, and Umansky [Phys. Plasmas 21, 055907 (2014)]; and (iii) Schurtz, Nicolaï, and Busquet's [Phys. Plasmas 7, 4238 (2000)] multigroup diffusion model (SNB). We find that while the EIC and NFLF models accurately predict the damping rate of a small-amplitude temperature perturbation (within 10% at moderate collisionalities), they overestimate the peak heat flow by as much as 35% and do not predict preheat in the more relevant case where there is a large temperature difference. The SNB model, however, agrees better with VFP results for the latter problem if care is taken with the definition of the mean free path. Additionally, we present for the first time a comparison of the SNB model against a VFP code for a hohlraum-relevant problem with inhomogeneous ionisation and show that the model overestimates the heat flow in the helium gas-fill by a factor of ?2 despite predicting the peak heat flux to within 16%.
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| 4. |
- Innocenti, M. E., et al.
(författare)
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Study of electric and magnetic field fluctuations from lower hybrid drift instability waves in the terrestrial magnetotail with the fully kinetic, semi-implicit, adaptive multi level multi domain method
- 2016
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 23:5
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Tidskriftsartikel (refereegranskat)abstract
- The newly developed fully kinetic, semi-implicit, adaptive multi-level multi-domain (MLMD) method is used to simulate, at realistic mass ratio, the development of the lower hybrid drift instability (LHDI) in the terrestrial magnetotail over a large wavenumber range and at a low computational cost. The power spectra of the perpendicular electric field and of the fluctuations of the parallel magnetic field are studied at wavenumbers and times that allow to appreciate the onset of the electrostatic and electromagnetic LHDI branches and of the kink instability. The coupling between electric and magnetic field fluctuations observed by Norgren et al. ["Lower hybrid drift waves: Space observations," Phys. Rev. Lett. 109, 055001 (2012)] for high wavenumber LHDI waves in the terrestrial magnetotail is verified. In the MLMD simulations presented, a domain ("coarse grid") is simulated with low resolution. A small fraction of the entire domain is then simulated with higher resolution also ("refined grid") to capture smaller scale, higher frequency processes. Initially, the MLMD method is validated for LHDI simulations. MLMD simulations with different levels of grid refinement are validated against the standard semi-implicit particle in cell simulations of domains corresponding to both the coarse and the refined grid. Precious information regarding the applicability of the MLMD method to turbulence simulations is derived. The power spectra of MLMD simulations done with different levels of refinements are then compared. They consistently show a break in the magnetic field spectra at k(perpendicular to)d(i) similar to 30, with d(i) the ion skin depth and k(perpendicular to) the perpendicular wavenumber. The break is observed at early simulated times, Omega(ci)t < 6, with Omega(ci) the ion cyclotron frequency. It is due to the initial decoupling of electric and magnetic field fluctuations at intermediate and low wavenumbers, before the development of the electromagnetic LHDI branch. Evidence of coupling between electric and magnetic field fluctuations in the wave-number range where the fast and slow LHDI branches develop is then provided for a cluster magnetotail crossing.
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| 5. |
- Koen, Etienne, et al.
(författare)
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A particle-in-cell approach to obliquely propagating electrostatic waves
- 2014
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 21:9
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Tidskriftsartikel (refereegranskat)abstract
- The electron-acoustic and beam-driven modes associated with electron beams have previouslybeen identified and studied numerically. These modes are associated with Broadband ElectrostaticNoise found in the Earth’s auroral and polar cusp regions. Using a 1-D spatial Particle-in-Cell sim-ulation, the electron-acoustic instability is studied for a magnetized plasma, which includes coolions, cool electrons and a hot, drifting electron beam. Both the weakly and strongly magnetizedregimes with varying wave propagation angle, h, with respect to the magnetic field are studied. Theamplitude and frequency of the electron-acoustic mode are found to decrease with increasing h.The amplitude of the electron-acoustic mode is found to significantly grow at intermediate wave-number ranges. It reaches a saturation level at the point, where a plateau forms in the hot electron velocity distribution after which the amplitude of the electron-acoustic mode decays
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| 6. |
- Koen, Etienne, et al.
(författare)
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Particle-in-cell simulations of ion-acoustic waves with application to Saturn's magnetosphere
- 2014
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 21:072122
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Tidskriftsartikel (refereegranskat)abstract
- Using a particle-in-cell simulation, the dispersion and growth rate of the ion-acoustic mode areinvestigated for a plasma containing two ion and two electron components. The electron velocitiesare modelled by a combination of two kappa distributions, as found in Saturn’s magnetosphere.The ion components consist of adiabatic ions and an ultra-low density ion beam to drive a veryweak instability, thereby ensuring observable waves. The ion-acoustic mode is explored for a rangeof parameter values such as j, temperature ratio, and density ratio of the two electron components.The phase speed, frequency range, and growth rate of the mode are investigated. Simulations ofdouble-kappa two-temperature plasmas typical of the three regions of Saturn’s magnetosphere are also presented and analysed.
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| 7. |
- Liu, Yueqiang, 1971, et al.
(författare)
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Modeling of resistive wall mode and its control in experiments and ITER
- 2006
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 13:5
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Tidskriftsartikel (refereegranskat)abstract
- Active control of the resistive wall mode (RWM) for DIII-D [Luxon and Davis, Fusion Technol. 8, 441 (1985)] plasmas is studied using the MARS-F code [Y. Q. Liu, Phys. Plasmas 7, 3681 (2000)]. Control optimization shows that the mode can be stabilized up to the ideal wall beta limit, using the internal control coils (I-coils) and poloidal sensors located at the outboard midplane, in combination with an ideal amplifier. With the present DIII-D power supply model, the stabilization is achieved up to 70% of the range between no-wall and ideal-wall limits. Reasonably good quantitative agreement is achieved between MARS-F simulations and experiments on DIII-D and JET (Joint European Torus) [P. H. Rebut, Nucl. Fusion 25, 1011 (1985)] on critical rotation for the mode stabilization. Dynamics of rotationally stabilized plasmas is well described by a single mode approximation; whilst a strongly unstable plasma requires a multiple mode description. For ITER [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)], the MARS-F simulations show the plasma rotation may not provide a robust mechanism for the RWM stabilization in the advanced scenario. With the assumption of ideal amplifiers, and using optimally tuned controllers and sensor signals, the present feedback coil design in ITER allows stabilization of the n=1 RWM for plasma pressures up to 80% of the range between the no-wall and ideal-wall limits.
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| 8. |
- Maler, D., et al.
(författare)
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Supersonic water jets as point-like sources of extremely high pressure
- 2023
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 30:2
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Tidskriftsartikel (refereegranskat)abstract
- Two interacting supersonic water jets and collisions of a water jet with an aluminum target are studied experimentally and by hydrodynamic simulations. Supersonic water jets form, when shocks generated by underwater electrical explosions of conical wire arrays converge. The arrays are supplied by a similar to 250kA, similar to 1 mu s rise time current pulse. Underwater explosion of two conical arrays placed face to face produces jets propagating in air with velocities of similar to 2.5 x 10(3) m/s leading to hot plasma formation at a temperature of similar to 2200-3000 K, pressure similar to 1.7 x 10(10) Pa, and density > 10(29) m(-3). When a single array explodes underwater in front of an aluminum target, the collision of the jet with the target produces a local pressure of similar to 3 x 10(10) Pa on the surface of the target.
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| 9. |
- Modestov, Mikhail, et al.
(författare)
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Bubble velocity in the nonlinear Rayleigh-Taylor instability at a deflagration front
- 2008
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 15:4, s. 12-
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Tidskriftsartikel (refereegranskat)abstract
- The Rayleigh-Taylor instability at a deflagration front is studied systematically using extensive direct numerical simulations. It is shown that, for a sufficiently large gravitational field, the effects of bubble rising dominate the deflagration dynamics. It is demonstrated both analytically and numerically that the deflagration speed is described asymptotically by the Layzer theory in the limit of large acceleration. In the opposite limit of small and zero gravitational field, intrinsic properties of the deflagration front become important. In that case, the deflagration speed is determined by the velocity of a planar front and by the Darrieus-Landau instability. Because of these effects, the deflagration speed is larger than predicted by the Layzer theory. An analytical formula for the deflagration speed is suggested, which matches two asymptotic limits of large and small acceleration. The formula is in good agreement with the numerical data in a wide range of Froude numbers. The present results are also in agreement with previous numerical simulations on this problem.
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| 10. |
- Shaing, KC, et al.
(författare)
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Local potato-plateau transport fluxes and a unified plateau theory
- 2002
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Ingår i: Physics of Plasmas. - 1089-7674 .- 1070-664X. ; 9:5, Part 1, s. 1654-1658
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Tidskriftsartikel (refereegranskat)abstract
- A local potato-plateau transport theory is presented. It is a nonradial averaged version of the original theory [Phys. Plasmas 4, 4331 (1997); 5, 953 (1998)]. The theory unifies conventional plateau theory and the potato-plateau theory. It is applicable at any radius. It is found that the ion heat conductivity is the same as that in the conventional theory in the region close to the magnetic axis. (C) 2002 American Institute of Physics.
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