| 1. |
|
|
| 2. |
- Antoni, V., et al.
(författare)
-
Turbulence and anomalous transport in magnetized plasmas : Hints from the reversed field pinch configuration
- 2004
-
Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 44:06-maj, s. 458-464
-
Tidskriftsartikel (refereegranskat)abstract
- The properties of plasma turbulence in the outer region of the Reversed Field Pinch experiments RFX and EXTRAP-T2R are reviewed. The statistical properties of fluctuations in the range of scales relevant for transport are presented. The observation of coherent structures emerging from the background turbulence and their interpretation in terms of vortices is reported. The interplay between these structures and the mean ExB flow of the plasma is demonstrated with emphasis to the action on the preferential rotation direction. The effect on the particle transport induced by the background turbulence and by the structures is discussed. Finally the methods tested to control turbulence and to mitigate the related transport are illustrated and discussed.
|
|
| 3. |
|
|
| 4. |
- Carbone, V, et al.
(författare)
-
To what extent can dynamical models describe statistical features of turbulent flows?
- 2002
-
Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 58:3, s. 349-355
-
Tidskriftsartikel (refereegranskat)abstract
- Statistical features of "bursty" behaviour in charged and neutral fluid turbulence are compared to statistics of intermittent events in a GOY shell model, and avalanches in different models of Self-Organized Criticality (SOC). It is found that inter-burst times show a power law distribution for turbulent samples and for the shell model, a property which is shared only in a particular case of the running sandpile model. The breakdown of self-similarity generated by isolated events observed in the turbulent samples is well reproduced by the shell model, while it is absent in all SOC models considered. On this base, we conclude that SOC models are not adequate to mimic fluid turbulence, while the GOY shell model constitutes a better candidate to describe the gross features of turbulence.
|
|
| 5. |
- Spolaore, M., et al.
(författare)
-
Vortex-induced diffusivity in reversed field pinch plasmas
- 2004
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 93:21
-
Tidskriftsartikel (refereegranskat)abstract
- Coherent structures identified in two reversed field pinch experiments are interpreted as a dynamic balance of dipolar and monopolar vortices growing and evolving under the effect of the ExB flow shear. For the first time their contribution to the anomalous transport has been estimated in fusion related plasmas, showing that they can account for up to 50% of the total plasma diffusivity. The experimental findings indicate that the diffusion coefficient associated with the coherent structures depends on the relative population of the two types of vortices and is minimum when the two populations are equal. An interpretative model is proposed to explain this feature.
|
|
| 6. |
- Carbone, V, et al.
(författare)
-
Intermittency and turbulence in a magnetically confined fusion plasma
- 2000
-
Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - : American Physical Society (APS). - 1539-3755 .- 1550-2376. ; 62:1, s. R49-R52
-
Tidskriftsartikel (refereegranskat)abstract
- The intermittency of the magnetic turbulence in reversed field pinch plasmas was measured. The probability distribution functions of magnetic field differences were not scale invariant because the wings of these functions were more important as the scales become smaller. This phenomena was identified as a classical signature of intermittency. The scaling laws also appeared very close to the external wall of the confinement device.
|
|
| 7. |
- Simancas, J. F., et al.
(författare)
-
Crustal structure of the transpressional Variscan orogen of SW Iberia : SW Iberia deep seismic reflection profile (IBERSEIS)
- 2003
-
Ingår i: Tectonics. - : AGU. - 0278-7407 .- 1944-9194. ; 22, s. 1062-
-
Tidskriftsartikel (refereegranskat)abstract
- IBERSEIS, a 303 km long (20 s) deep seismic reflection profile, was acquired across the Variscan belt in SW Iberian Peninsula. The acquisition parameters were designed to obtain a high-resolution crustal-scale image of this orogen. The seismic profile samples three major tectonic terranes: the South Portuguese Zone, the Ossa-Morena Zone, and the Central Iberian Zone, which were accreted in Late Paleozoic times. These terranes show a distinctive seismic signature, as do the sutures separating them. Late strike-slip movements through crustal wedges are apparent in the seismic image and have strongly modified the geometry of sutures. The upper crust appears to be decoupled from the lower crust all along the seismic line, but some deformation has been accommodated at deeper levels. A sill-like structure is imaged in the middle crust as a 1–2 s thick and 175 km long high-amplitude conspicuous reflective band. It is interpreted as a great intrusion of mafic magma in a midcrustal decollement. Taking into account surface geological data and the revealed crustal architecture, a tectonic evolution is proposed for SW Iberia which includes transpressional collision interacting during Early Carboniferous with a mantle plume. The Moho can be identified along the entire transect as subhorizontal and located at 10 to 11 s, indicating a 30–35 km average crustal thickness. Its seismic signature changes laterally, being very reflective beneath the South Portuguese Zone and the Central Iberian Zone, but discontinuous and diffuse below the Ossa Morena Zone.
|
|
| 8. |
- Sorriso-Valvo, Luca, et al.
(författare)
-
Intermittency in plasma turbulence
- 2001
-
Ingår i: Planetary and Space Science. - 0032-0633 .- 1873-5088. ; 49:12, s. 1193-1200
-
Tidskriftsartikel (refereegranskat)
|
|
| 9. |
- Van Oost, G., et al.
(författare)
-
Turbulent transport reduction by E x B velocity shear during edge plasma biasing : recent experimental results
- 2003
-
Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 45:5, s. 621-643
-
Tidskriftsartikel (refereegranskat)abstract
- Experiments in the tokamaks TEXTOR, CASTOR, T-10 and ISTTOK, as well as in the reversed field pinch RFX have provided new and complementary evidence on the physics of the universal mechanism of E x B velocity shear stabilization of turbulence, concomitant transport barrier formation and radial conductivity by using various edge biasing techniques. In TEXTOR the causality between transport reduction and induced electric fields in the edge has been for the first time clearly demonstrated. The high electric field gradients have been identified as the cause for the quenching of turbulent cells. A quantitative analysis of the measured transport reduction is in good agreement with theoretical predictions. The scaling of plasma turbulence suppression with velocity shear has been established, revealing the density-potential cross-phase as a key element. Reduction in poloidal electric field, temperature, and density fluctuations across the shear layer lead to a reduction of the anomalous conducted and convected heat fluxes resulting in an energy transport barrier that is measured directly. In CASTOR the biasing electrode is placed at the separatrix in a non-intrusive configuration which has demonstrated strongly sheared electric fields and consequent improvement of the global particle confinement, as predicted by theory. The impact of sheared E x B flow on edge turbulent structures has been measured directly using a comprehensive set of electrostatic probe arrays as well as emissive probes. Measurements with a full poloidal Langmuir probe array have revealed quasi-coherent electrostatic waves in the SOL with a dominant mode number equal to the edge safety factor. In T-10 edge biasing is clearly improving the global performance of ECR heated discharges. Reflectometry and heavy ion beam probe measurements show the existence of a narrow plasma layer with strong suppression of turbulence. On ISTTOK, the influence of alternating positive and negative electrode and (non-intrusive) limiter biasing has been compared. Electrode biasing is found to be more efficient in modifying the radial electric field E, and confinement, limiter biasing acting mainly on the SOL. In the RFX reversed field pinch it has been demonstrated that also in RFPs biasing can increase the local E x B velocity shear in the edge region, and hence substantially reduce the local turbulence driven particle flux mainly due to a change in the relative phase between potential and density fluctuations.
|
|
