Thermal load distribution on the ALT-II limiter of TEXTOR-94 during RI mode operation and during disruptions

Abstract

Abstract. Thermographic measurements using an IR scanner have been performed at the pump limiter ALT-II of TEXTOR-94 during RI mode discharges and during disruptions. The measurements on the RI mode discharges were done to complete the TEXTOR database which had shown a structured decay pattern of the deposited power. It was found that the underlying radial heat flux can be described by two exponential decay functions. This structure, which generates an unexpected heat component close to the tangent line, has been observed in all discharge conditions including the RI mode. During disruptions, the heat is released in short pulses with a typical duration of 0.01-0.1 ms. The radial decay length of these pulses has a similar shape to the heat flux during normal discharges: it consists again of a strong component close to the tangent line with a radial decay length of 2-5 mm and probably one with a decay length of the order of 1 cm. The heat is released at the time when the edge electron temperature of the plasma drops, when intense hydrogen and carbon fluxes occur near the walls, and when electrical currents in the limiter blades are excited. In a tentative interpretation, the temporal and spatial structure of the heat pulse is attributed to the presence and growth of a laminar zone at the plasma edge, which is connected with the ergodization of the plasma edge during a disruption.

Turbulent transport regimes and the scrape-off layer heat flux width

“…When predicted turbulent SOL widths exceed the HD neoclassical estimate, qq s , it is reasonable to assume that turbulence is the dominant mechanism, although a twoscale-length SOL might also be possible in this case. 26,67 In the opposite limit where the turbulence-generated width is less than the ion orbit excursion, k q < qq s turbulence is likely irrelevant, or at least, its effects must be computed in the context of neoclassical orbit physics. This limits the rightmost extent of the diagram in Fig.…”

A synchrotron radiation diagnostic to observe relativistic runaway electrons in a tokamak plasma

“…Recently, the electronics have been upgraded and all signals are digitized to 12 bits before they are transferred by fiber optics to the remote computer for data analysis and storage. 11 Moreover, to avoid electric or magnetic interference ͑especially during a disruption, when the generation of runaway electrons preserves special attention͒, the camera head and the electronic box are both well shielded by an iron housing with an internal copper foil.…”

High resolution temperature and density profiles during the energy quench of density limit disruptions in Rijnhuizen tokamak project

“…Nonetheless, a detailed physical understanding of their time evolution has still not been fully accomplished. 2 Experimentally, [3][4][5][6][7][8][9][10][11] the difficulties in probing the disruption are mainly connected with its extremely short duration ͑mi-croseconds͒, unpredictable onset and 3D structure. Also, except for electron temperature and density, local plasma parameters are difficult to measure, or are not measured at all.…”