| 1. |
- Anderson, Johan, 1973, et al.
(författare)
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Effects of cross-sectional elongation on the resistive edge modes
- 2001
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 8, s. 180-
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Tidskriftsartikel (refereegranskat)abstract
- Resistive edge modes in a shifted noncircular tokamak geometry are investigated in the electrostatic limit. The reduced Braghinskii equations are used as a model for the electrons and an advanced fluid model for the ions. An eigenvalue problem is derived from these equations which is solved numerically. It is found that the resistive ballooning modes are stabilized by plasma elongation forpeaked density profiles. In addition, it is found that the resistive ITG mode may be either stabilized or destabilized by elongation depending on the collision frequency.
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| 2. |
- Anderson, Johan, 1973, et al.
(författare)
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Effects of non-circular tokamak geometry on ion-temperature-gradient driven modes
- 2000
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Ingår i: Plasma Phys. Contr. Fusion. - : IOP Publishing. ; 42, s. 545-
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Tidskriftsartikel (refereegranskat)abstract
- The influence of plasma elongation and Shafranov shift on the stability of electrostatic ion-temperature-gradient driven modes (ηi-modes) is investigated. An advanced fluid model is used for the ions together with Boltzmann distributed electrons. The derived eigenvalue equation is solved both analytically, in the strong ballooning limit, and numerically. It is found that the effects of elongation change from stabilizing, for peaked density profiles, to destabilizing in the flat density regime. In addition, it is shown that the maximum growth rate is shifted towardsshorter wavelengths as the elongation increases. The effects of shaping on tokamak stability are exemplified with data from a Joint European Torus (JET) high-performance mode discharge.
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| 3. |
- Anderson, Johan, 1973, et al.
(författare)
-
Zonal flow generation in ITG turbulence
- 2002
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 9, s. 4500-
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Tidskriftsartikel (refereegranskat)abstract
- In the present work the zonal flow (ZF) growth rate in toroidal ion-temperature-gradient (ITG) mode turbulence including the effects of elongation is studied analytically. The scaling of the ZF growth with plasma parameters is examined for typical tokamak parameter values. The physical model used for the toroidal ITG driven mode is based on the ion continuity and ion temperature equations whereas the ZF evolution is described by the vorticity equation. The results indicate that a large ZFgrowth is found close to marginal stability and for peaked density profiles and these effects may be enhanced by elongation.
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| 4. |
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| 5. |
- Rafiq, Tariq, et al.
(författare)
-
EFFECTS OF MICROTEARING MODES ON THE EVOLUTION OF ELECTRON TEMPERATURE PROFILES IN HIGH COLLISIONALITY NSTX DISCHARGES
- 2018
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Ingår i: IAEA Fusion Energy Conference. ; 27
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Konferensbidrag (refereegranskat)abstract
- A goal of this research project is to describe the evolution of the electron temperature profiles in high collisionality NSTX H-mode discharges. Gyrokinetic simulations indicate that microtearing modes (MTMs) are a source of significant electron thermal transport in these discharges. In order to understand the effect MTMs have on transport and, consequently, on the evolution of electron temperature in NSTX discharges, a reduced transport model for MTMs has been developed. The dependence of the MTM real frequency and growth rate on plasma parameters, appropriate for high collisionality NSTX discharges, is obtained employing the new MTM transport model. The dependencies on plasma parameters are compared and found to be consistent with MTM results obtained using the gyrokinetic GYRO code. The MTM real frequency, growth rate, magnetic fluctuations and resulting electron thermal transport are examined for high collisionality NSTX discharges in systematic scans over plasma parameters. In earlier studies it was found that the version of the Multi-Mode (MM) transport model, that did not include the effect of MTMs, provided a suitable description of the electron temperature profiles in high collisionality standard tokamak discharges. That version of the MM model included contributions to electron thermal transport from the ion temperature gradient, trapped electrons, kinetic ballooning, peeling ballooning, collisionless and collision dominated MHD modes, and electron temperature gradient modes. When the MM model, that includes transport associated with MTMs, is installed in the TRANSP code and is utilized in studying electron thermal transport in high collisionality NSTX discharges, it is found that agreement with the experimental electron temperature profile is significantly improved.
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| 6. |
- Rafiq, Tariq, 1971, et al.
(författare)
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Microtearing Modes in Low Collisionality NSTX Discharges
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Recently, a new unified fluid/kinetic MTM model is developed and incorporated into the Multi-Mode Model (MMM). The MTM model has been found to reproduce many of the linear gyrokinetic results predicted in NSTX discharges, such as the variation of real frequency and growth rates with poloidal wavenumber, beta, and electron temperature (T e ) and density gradients. A particularly important result is that the model recovers the non-monotonic dependence of linear MTM growth rate with collision frequency.
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| 7. |
- Rafiq, Tariq, 1971, et al.
(författare)
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PLASMA PROFILE PREDICTION IN NSTX DISCHARGES USING THE UPDATED MULTI-MODE ANOMALOUS TRANSPORT MODULE
- 2023
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Ingår i: Fusion Energy Conference. ; 29
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Konferensbidrag (refereegranskat)abstract
- The objective of this study is twofold: firstly, to demonstrate the consistency between the anomalous transport results produced by updated Multi-Mode Model (MMM) version 9.1 and those obtained through gyrokinetic simulations; and secondly, to showcase MMM’s ability to predict electron and ion temperature profiles in low aspect ratio, high beta NSTX discharges. MMM encompasses a range of transport mechanisms driven by electron and ion temperature gradients, trapped electrons, kinetic ballooning, peeling, microtearing, and drift resistive inertial ballooning modes. These modes within MMM are being verified through corresponding gyrokinetic results. The modes that potentially contribute to ion thermal transport are stable in MMM, aligning with both experimental data and findings from linear CGYRO simulations. The isotope effects on these modes are also studied and found to be stabilizing, consistent with the experimental trend. The electron thermal power across the flux surface is computed within MMM and compared to experimental measurements and nonlinear CGYRO simulation results. Specifically, the electron temperature gradient modes (ETGM) within MMM account for 2.0 MW of thermal power, consistent with experimental findings. It is noteworthy that the ETGM model requires approximately 5.0 ms of computation time on a standard desktop, while nonlinear CGYRO simulations necessitate 8.0 hours on 8 K cores. MMM proves to be highly computationally efficient, a crucial attribute for various applications, including real-time control, tokamak scenario optimization, and uncertainty quantification of experimental data.
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| 8. |
- Rafiq, T, et al.
(författare)
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Predictive modeling of NSTX discharges with the updated multi-mode anomalous transport module
- 2024
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Ingår i: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 64:7
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study is twofold: firstly, to demonstrate the consistency between the anomalous transport results produced by updated Multi-Mode Model (MMM) version 9.0.4 and those obtained through gyrokinetic simulations; and secondly, to showcase MMM’s ability to predict electron and ion temperature profiles in low aspect ratio, high beta NSTX discharges. MMM encompasses a range of transport mechanisms driven by electron and ion temperature gradients, trapped electrons, kinetic ballooning, peeling, microtearing, and drift resistive inertial ballooning modes. These modes within MMM are being verified through corresponding gyrokinetic results. The modes that potentially contribute to ion thermal transport are stable in MMM, aligning with both experimental data and findings from linear CGYRO simulations. The isotope effects on these modes are also studied and higher mass is found to be stabilizing, consistent with the experimental trend. The electron thermal power across the flux surface is computed within MMM and compared to experimental measurements and nonlinear CGYRO simulation results. Specifically, the electron temperature gradient modes (ETGM) within MMM account for 2.0 MW of thermal power, consistent with experimental findings. It is noteworthy that the ETGM model requires approximately 5.0 ms of computation time on a standard desktop, while nonlinear CGYRO simulations necessitate 8.0 h on 8 K cores. MMM proves to be highly computationally efficient, a crucial attribute for various applications, including real-time control, tokamak scenario optimization, and uncertainty quantification of experimental data.
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| 9. |
- Rafiq, Tariq, 1971, et al.
(författare)
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Statistical validation of multi-mode model for anomalous transport to high beta and ITB tokamak scenarios in KSTAR
- 2019
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Ingår i: Bulletin of the American Physical Society. ; 64:11
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Multi-Mode anomalous transport model is validated employing experimental data for superconducting KSTAR NBI heated tokamak discharges that represent a high beta poloidal, high beta normalized, and ITB long pulse scenarios. The Multi-Mode model computes the anomalous transport driven by the ITG, TEM, ETG, KBM, RBM, and PB modes. In addition, recent modification to the model allows the computation of the anomalous transport driven by the microtearing modes. The validation study is carried out using integrated modeling simulations that employ the numerical PT-SOLVER in the TRANSP code and that utilizes the KSTAR experimental boundary and initial conditions. The equilibrium data is interpolated from EFIT reconstruction. NBI heating and current drive are obtained using NUBEAM. Neoclassical transport is calculated using the Chang-Hinton model. The predicted evolving temperature profiles are compared with the corresponding KSTAR experimental data. The comparison is quantified by calculating the RMS deviations and Offsets.
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