| 1. |
- Tegnered, Daniel, 1987, et al.
(författare)
-
Gyrokinetic simulations of particle transport in pellet fuelled JET discharges
- 2017
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP PUBLISHING LTD. - 0741-3335 .- 1361-6587. ; 59:10
-
Tidskriftsartikel (refereegranskat)abstract
- Pellet injection is a likely fuelling method of reactor grade plasmas. When the pellet ablates, it will transiently perturb the density and temperature profiles of the plasma. This will in turn change dimensionless parameters such as a/L-n, a/L-T and plasma beta. The microstability properties of the plasma then changes which influences the transport of heat and particles. In this paper, gyrokinetic simulations of a JET L-mode pellet fuelled discharge are performed. The ion temperature gradient/trapped electron mode turbulence is compared at the time point when the effect from the pellet is the most pronounced with a hollow density profile and when the profiles have relaxed again. Linear and nonlinear simulations are performed using the gyrokinetic code GENE including electromagnetic effects and collisions in a realistic geometry in local mode. Furthermore, global nonlinear simulations are performed in order to assess any nonlocal effects. It is found that the positive density gradient has a stabilizing effect that is partly counteracted by the increased temperature gradient in the this region. The effective diffusion coefficients are reduced in the positive density region region compared to the intra pellet time point. No major effect on the turbulent transport due to nonlocal effects are observed.
|
|
| 2. |
- Eriksson, Frida, 1986, et al.
(författare)
-
Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating
- 2017
-
Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2481 .- 1745-2473. ; 13:10, s. 973-978
-
Tidskriftsartikel (refereegranskat)abstract
- We describe a new technique for the effcient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed 'three-ion' scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate effcient acceleration of 3He ions to high energies in dedicated hydrogen-deuterium mixtures. Simultaneously, effective plasma heating is observed, as a result of the slowing-down of the fast 3He ions. The developed technique is not only limited to laboratory plasmas, but can also be applied to explain observations of energetic ions in space-plasma environments, in particular, 3He-rich solar flares.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Tegnered, Daniel, 1987
(författare)
-
Gyrokinetic simulations of microturbulence and transport in tokamak plasmas
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fusion power is one of few viable and sustainable means of energy production. The tokamak is arguable the most mature technology to magnetically confine fusion plasmas. In these devices, heat and particle transport is dominated by small-scale turbulent fluctuations. Using high performance computing resources these phenomena can be studied in detail through numerical experiments. The Joint European Torus (JET) is currently the largest tokamak in operation. Recently, the plasma facing components of JET were changed from carbon to metal — beryllium and tungsten. This in order to better align with the design foreseen for ITER, a next-generation device under construction in Cadarache in France. With this new wall, new impurities were introduced into the plasma. Impurities, any ion that is not a reactant in the fusion reactions, are detrimental to the fusion power as they dilute the plasma and can radiate energy. It is therefore important to study the transport of impurities and how it is affected by different operational parameters. The change of wall material has also led to a degradation in energy confinement for certain types of discharges at JET. Energy confinement must be optimized in future fusion devices for them to be economically viable. Another important issue for ITER is the refuelling of the plasma through pellet injection. The frozen hydrogen pellets are injected at high speed into the plasma. When they ablate, they perturb the density and temperature profiles. This changes the properties of the microturbulence which might hinder the particles from reaching the core of the plasma. The present thesis aims at an improved understanding of these urgent issues by means of gyrokinetic simulations of particle and heat transport driven by Ion Temperature Gradient (ITG) and Trapped Electron (TE) mode turbulence.
|
|
| 7. |
- Tegnered, Daniel, 1987, et al.
(författare)
-
Impact of a hollow density profile on turbulent particle fluxes: Gyrokinetic and fluid simulations
- 2017
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 24:7, s. Artno: 072303-
-
Tidskriftsartikel (refereegranskat)abstract
- Hollow density profiles may occur in connection with pellet fuelling and L to H transitions. A positive density gradient could potentially stabilize the turbulence or change the relation between convective and diffusive fluxes, thereby reducing the turbulent transport of particles towards the center, making the pellet fuelling scheme inefficient. In the present work, the particle transport driven by Ion Temperature Gradient/Trapped Electron (ITG/TE) mode turbulence in hollow density profiles is studied by fluid as well as gyrokinetic simulations. The fluid model used, an extended version of the Weiland transport model, Extended Drift Wave Model (EDWM), incorporates an arbitrary number of ion species in a multi-fluid description and an extended wavelength spectrum. The fluid model, which is fast and hence suitable for use in predictive simulations, is compared to gyrokinetic simulations using the code GENE. Typical tokamak parameters are used based on the Cyclone Base Case. Parameter scans in key plasma parameters like plasma β, R/LT, and magnetic shear are investigated. In addition, the effects of a fast species are studied and global ITG simulations in a simplified physics description are performed in order to investigate nonlocal effects. It is found that β in particular, has a stabilizing effect in the negative R/Ln region. Both nonlinear GENE and EDWM simulations show a decrease in inward flux for negative R/Ln and a change in the direction from inward to outward for positive R/Ln. Moreover, the addition of fast particles was shown to decrease the inward main ion particle flux in the positive gradient region further. This might have serious consequences for pellet fuelling of high β plasmas. Additionally, the heat flux in global ITG turbulence simulations indicates that nonlocal effects can play a different role from usual in connection with pellet fuelling.
|
|
