2.1. Contextualización del enfoque de competencias laborales
2.1.2. Contextualización de las competencias laborales a nivel internacional
4.8
The structure of the heat fluxes in the plasma
edge
As discussed in section 4.7 the misalignment of the tiles causes “shadows” some of the heat influxes onto the divertor target plates. It makes serious encumbrances in analysis of the structure of the power flux tubes towards the divertor target plates. However, analysis of the shadowed and overexposed regions can give some hints to understanding the structure of the heat fluxes and the laminar zone. In figure 4.14
the temperature distribution on the DED target plates for two cases is presented. In figure 4.14a we see the temperature distribution on the DED target plates for relatively low ergodization level: The stripes are not separated. The black spots at the toroidal angle ϕ = 195◦ in the infrared view are the results of the image
processing. To enhance the contrast of the image we subtract frames recorded before the switch on of the DED from those recorded during the DED operation. This procedure reduces the signals coming from the overheated areas, because this spot is heated already before the DED was switched on. This allows to bring out the structure of the power flux stripes. The tiles, which have the right edge at ϕ = 195◦, protrude from the divertor surface towards the plasma core. Hence the
shadowed and overheated regions appear in the vicinity of this edge. The analysis of the temperature distribution shows that each of the power stripe consist of two parts: The particle and heat fluxes are approaching the target plates from different toroidal direction, depending on which part of the power stripe they are deposited. The toroidal directions of incoming heat fluxes are visualized with yellow arrows. If we consider the sequence of overheating and shadowing in figure 4.14, we can see that the heat forming the upper part of the power stripes comes from the right hand side and it is shadowed on the left hand side of the protruding edge. The heat flux density deposited in the lower part of the power stripe comes from the left hand side and it is shadowed on the right hand side of the protruding edge.
If the level of ergodization is increased (see figure 4.14b), as it was a case during the discharge #93100, we can clearly see that the two power stripes in the middle are split up completely forming the area in between the pair of strike zones, where
98 CHAPTER 4. THERMOGRAPHIC MEASUREMENTS a)
Q
||,G
|| 0 100 200 300 400 500 600 165 170 175 180 185 190 195 200 205 210 [deg] j s[mm] b) 165 170 175 180 185 190 195 200 205 210 0 100 200 300 400 500 600 6 7Q
||,G
|| [deg] j s[mm]Figure 4.14: The temperature distribution on the surface of the divertor for: a) low ergodization case (discharge #92596) and b) high ergodization case (discharge #93100). The yellow arrows indicate the direction of incoming heat and particle fluxes.
4.8. HEAT FLUXES IN THE PLASMA EDGE 99 there is almost no incoming heat flux. It is consistent with the results from Atlas, where at the higher level of ergodization a magnetic footprint stripe split up and forms the private flux zone. Here the ergodization is increased by changing the plasma position: From R0 = 1.74 m in the discharge #92596 to a R0 = 1.72 m in
#931001. Apart of the splitting of the power stripes the structure remains similar:
We see two parts of the stripe formed by the heat fluxes coming from two different toroidal direction.
This observation is consistent with the modelling of the laminar zone by Atlas in
stagnation point private flux Q|| || , G Q || || , G
Figure 4.15: The schematic illustration of the topology of the single turn flux tube in the laminar zone of the TEXTOR-DED experiment. The blue line represents a field line with Lc = 1 in the poloidal projection. The yellow arrows show the direction of
the parallel particle Γ|| and heat fluxes Q||.
section 3.6. Namely, the magnetic footprint stripes are formed by the field lines coming from two different toroidal directions (see also figure 3.17), which at the higher level of ergodization form a pair of stripes separated by the private flux zone. The model also shows that each of the footprint stripes is formed by two intersections of the single turn magnetic flux tube with the wall. The schematic illustration of the topology of the single turn flux tube is presented in figure 4.15. The blue line represents the field line with Lc = 1 in the poloidal projection. According to the
100 CHAPTER 4. THERMOGRAPHIC MEASUREMENTS
modelling [9,13,26], in a well developed laminar zone the parallel transport of heat and particles in the plasma edge predominantly takes place along the single turn flux tubes. The power and particle deposition pattern is formed by the two flows from the stagnation point (marked with yellow arrows). The structure of the flows along the Lc = 1 flux tube is very similar to the scrape-off layer of the poloidal
divertor. However due to contributions of flux tubes with longer connection lengths the topology is more complicated.