| 1. |
- Anderson, Johan, 1973, et al.
(författare)
-
Effects of the Second Harmonic and Plasma Shaping on the Geodesic Acoustic Mode
- 2014
-
Ingår i: 41st EPS conference, Berlin, 23.- 27.6.2014. ; :P1.056, s. 4-
-
Konferensbidrag (refereegranskat)abstract
- The effects of second harmonics of the density and temperature perturbations on the linear Geodesic Acoustic Mode (GAM) frequency and non-linear generation of the GAM are investigated, using a fluid model. We show that the second harmonics contribute to the frequency through the density gradient scale length and the wave number of the GAM. In addition, the linear frequency of the GAM is generally increased by coupling to the higher harmonic.
|
|
| 2. |
- Anderson, Johan, 1973, et al.
(författare)
-
Effects of the Second Harmonic on the GAM in Electron Scale Turbulence
- 2013
-
Ingår i: European Fusion Theory Conference. ; 15, s. 10-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The effects higher order harmonics have been self-consistently includedin the derivation of the electron branch of the electron Geodesic Acoustic Mode (el-GAM) in an Electron-Temperature-Gradient (ETG) turbulence background. The workis based on a two-fluid model including finite β-effects while retaining non-adiabaticions. In solving the linear dispersion relation, it is found that the due to the couplingto the m = 2 mode the real frequency may be significantly altered and yield highervalues.
|
|
| 3. |
- Anderson, Johan, 1973, et al.
(författare)
-
Electron Geodesic Acoustic Modes in Electron Temperature Gradient Mode Turbulence
- 2012
-
Ingår i: Proceedings 39th EPS/16th ICPP, Stockholm 2-6 July 2012. - 9781622769810 ; 2, s. 814-817
-
Konferensbidrag (refereegranskat)abstract
- There has been overwhelming evidence that coherent structures such as vortices, streamers and zonal flows (m = n = 0, where m and n are the poloidal and toroidal modenumbers respectively) play a critical role in determining the overall transport in magnetically confined plasmas. The Geodesic Acoustic Mode (GAM) is the oscillatory counterpart of the zonal flow (m = n = 0 in the potential perturbation, m = 1, n = 0 in the perturbations in density, temperature and parallel velocity) and thus a much weaker effect on turbulence is expected. Nevertheless experimental studies suggest that GAMs (n = 0, m = 1) are related to the L-H transition and transport barriers. The electron-temperature-gradient (ETG) mode driven by a combination of electron temperature gradients and field line curvature effects is a likely candidate for driving electron heat transport. The ETG mode driven electron heat transport is determined by short scale fluctuations that do not influence ion heat transport and is largely unaffected by the large scale flows stabilizing ion-temperature-gradient (ITG) modes. We have utilized a fluid model for the ETG mode based on the Braghinskii equations with non-adiabatic ions including impurities and finite β - effects. The ETG mode model consists of electron continuity, electron parallel momentum and energy equations in combination of an non-adiabatic ion response. The ion and electron counterparts are coupled using quasineutrality. We use the wave kinetic equation to describe the background short scale ETG turbulence and derive an dispersion relation for the GAM. In describing the large scale plasma flow dynamics it is assumed that there is a sufficient spectral gap between the small scale fluctuations and the large scale flow. We note that the linear GAM is purely oscillatory and non-linearly the electron GAM is unstable with a growth rate depending on the saturation level |φk|2. To estimate the ETG turbulent fluctuation level and GAM growth, a predator-prey model was used to describe the coupling between the GAMs and small scale ETG turbulence. The stationary point of the coupled system implies that the ETG saturation level φk can be drastically enhanced by a new saturation mechanism, stemming from a balance between the Landau damping and the GAM growth rate.
|
|
| 4. |
- Anderson, Johan, 1973, et al.
(författare)
-
Electron geodesic acoustic modes in electron temperature gradient mode turbulence
- 2012
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 19:8
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, the first demonstration of an electron branch of the geodesic acoustic mode (el-GAM) driven by electron temperature gradient (ETG) modes is presented. The work is based on a fluid description of the ETG mode retaining non-adiabatic ions and the dispersion relation for el-GAMsdriven nonlinearly by ETG modes is derived. A new saturation mechanism for ETG turbulence through the interaction with el-GAMs is found, resulting in a significantly enhanced ETGturbulence saturation level compared to the mixing length estimate.
|
|
| 5. |
- Anderson, Johan, 1973, et al.
(författare)
-
High frequency geodesic acoustic modes in electron scale turbulence
- 2013
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:12, s. article nr. 123016-
-
Tidskriftsartikel (refereegranskat)abstract
- In this work the finite β-effects of an electron branch of the geodesic acoustic mode (el-GAM) driven by electron temperature gradient (ETG) modes is presented. The work is based on a fluid description of the ETG mode retaining non-adiabatic ions and the dispersion relation for el-GAMs driven non-linearly by ETG modes is derived. The ETG growth rate from the fluid model is compared with the results found from gyrokinetic simulations with good agreement. A new saturation mechanism for ETG turbulence through the interaction with el-GAMs is found, resulting in a significantly enhanced ETG turbulence saturation level compared with the mixing length estimate. It is shown that the el-GAM may be stabilized by an increase in finite β as well as by increasing non-adiabaticity. The decreased GAM growth rates is due to the inclusion of the Maxwell stress.
|
|
| 6. |
- Anderson, Johan, 1973, et al.
(författare)
-
High Frequency Geodesic Acoustic Modes in Electron Scale Turbulence
- 2012
-
Ingår i: Proceedings 24th IAEA FEC, San Diego 8-13 October 2012.
-
Konferensbidrag (refereegranskat)abstract
- In this work the first demonstration of a high frequency branch of the geodesic acoustic mode (GAM) driven by electron temperature gradient (ETG) modes is presented. The work is based on a fluid description of the ETG mode retaining non-adiabatic ions and the dispersion relation for high frequency GAMs driven nonlinearly by ETG modes is derived. A new saturation mechanism for ETG turbulence through the interaction with high frequency GAMs is found, resulting in a significantly enhanced ETG turbulence saturation level compared to the mixing length estimate.
|
|
| 7. |
- Anderson, Johan, 1973, et al.
(författare)
-
Saturation Level of ETG Turbulence
- 2013
-
Ingår i: Festival de Thorie. ; 7, s. 4-
-
Konferensbidrag (refereegranskat)abstract
- In this work the finite β-effects of an electron branch of the geodesicacoustic mode (el-GAM) driven by electron temperature gradient (ETG) modes ispresented. The work is based on a fluid description of the ETG mode retaining nonadiabaticions and the dispersion relation for el-GAMs driven non-linearly by ETGmodes is derived. The ETG growth rate from the fluid model is compared to the resultsfound from gyrokinetic simulations with good agreement. A new saturation mechanismfor ETG turbulence through the interaction with el-GAMs is found, resulting in asignificantly enhanced ETG turbulence saturation level compared to the mixing lengthestimate. It is shown that the el-GAM may be stabilized by an increase in finite β aswell as by increasing non-adiabaticity. The decreased GAM growth rates is due to theinclusion of the Maxwell stress.
|
|
| 8. |
- Anderson, Johan, 1973, et al.
(författare)
-
Zonal flow generation in ITG turbulence
- 2002
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 9, s. 4500-
-
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.
|
|
| 9. |
- Skyman, Andreas, 1982, et al.
(författare)
-
Particle transport in ion and electron scale turbulence
- 2012
-
Ingår i: Proceedings of 24th Fusion Energy Conference -- IAEA CN-197.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This work deals with transport of main ions and impurities in micro turbulence driven by ion and electron temperature gradients, and trapped electrons. Results are obtained for both non- and quasi-linear simulations, using the gyrokinetic code GENE. Transport properties are quantified by the gradient of zero particle flux for steady state in source free regions.Results are compared with results obtained using a computationally efficient fluid model. Of particular interest are conditions of steep gradients, relevant to eg. transport barriers. Results from s–α geometry are compared with results with a JET-like magnetic equilibrium, and the effects on transport investigated. Further, the quality of He ash removal is studied.
|
|
| 10. |
- Skyman, Andreas, 1982, et al.
(författare)
-
Particle transport in ion and electron scale turbulence
- 2012
-
Ingår i: Proceedings of 24th Fusion Energy Conference -- IAEA CN-197.
-
Konferensbidrag (refereegranskat)abstract
- Micro turbulent modes have important and non-trivial effects on transport in tokamaks. This paper deals with transport of main ions and impurities in ion and electron scale turbulence, driven by ion and electron temperature gradients, and trapped electrons. Using the gyrokinetic Vlasov code GENE, results are obtained from both nonlinear and quasi-linear simulations. The transport properties are quantified by calculating the gradient of zero particle flux for steady state in source free regions of the plasma. The results are compared and contrasted with results obtained using a computationally efficient fluid model.Of particular interest are conditions of steep gradients, relevant to e.g. transport barrier conditions. Further, results from a simple s–α geometry are compared with results obtained using a JET-like magnetic equilibrium, and the effects on transport investigated.
|
|
