The cumulative impact of the inhomogeneous distribution of the plasma temperature and electromagnetic effects on dynamics of plasma filaments in the hot edge plasma of a tokamak, characterized by ...small values of the parameter
, is analyzed. The physical model describing the filament dynamics is presented. Estimates of the scrape-off-layer plasma parameters, for which electromagnetic and temperature effects can have a substantial impact on the filament dynamics in conditions of the low ratio of the plasma pressure to the pressure of the magnetic field, are obtained. The model equations are used for three-dimensional simulations of the macroscopic motion of filaments in plasma, the parameters of which are similar to the parameters of the peripheral plasma of the tokamak T-15MD, for different types of the spatial distribution of the electron temperature inside the filaments. It is shown that simultaneously taking electromagnetic and temperature effects into account can lead to a considerable departure of the filament trajectories of motion from those in the electrostatic case.
Recent improvements in the superconducting performance and technical maturity of high-temperature-superconductors (HTS) lead to considerations of using HTS in future fusion magnets in addition to the ...presently used low-temperature superconductors (LTS). Compact high field magnet systems entirely made of HTS for compact tokamaks, hybrid HTS-LTS magnets for enhanced operational capabilities (e.g. larger flux swing) in conventional tokamaks and future stellarator devices with HTS magnet systems are presently investigated. An overview of recent concepts, developments and designs of HTS-based future fusion magnet systems is given and a number of physical and technical challenges will be addressed, too: In particular, the so-called second generation HTS Rare-Earth-Barium-Copper-Oxide (REBCO) shows an excellent superconducting performance over a wide range of magnetic fields and temperatures. The layered architecture of these technical REBCO conductors and the ceramic nature of REBCO lead to mechanical challenges at high Lorentz forces, which is relevant for cable-in-conduit-conductors (CICC) of future fusion magnets due to the high currents and high field strengths. Different high-current cable concepts for future fusion magnets are discussed. High loads are not only a challenge for potential future HTS conductors but also for the conductor jackets and the coil casing of the magnet systems. An increase of the numbers of load cycles on the path towards a future fusion power plant requires superior mechanical strength. The high critical temperature of HTS materials allows to design HTS CICC with a noticeably higher minimum quench energy and temperature margin compared to LTS conductors – but leads inevitably to substantially slower quench propagation velocity and challenges related to quench detection. Recent results from numerical modeling and experimental investigation of quench in high-current HTS CrossConductor (HTS CroCo) based CICC are addressed.
In present day tokamaks, the role of the control research is to support the physics experiments and to prepare technologies for future devices such as ITER and DEMO. This paper presents the ...developments done under the MST1 program collaboration on ASDEX Upgrade in the area of the actuator management, plasma density reconstruction, and feedback control of the electron temperature. In the area of actuator management, the actuator interface was unified for the neutral beams and for the gyrotrons, which enables to freely group these actuators to bigger objects, so called virtual actuators. In the area of plasma state reconstruction, a significant progress was made in the real time estimation of the plasma density in discharges with ion cyclotron heating. This enabled execution of experiments requiring electron temperature control in discharges with ion cyclotron heating, which are reported as well. Other control applications such as fusion power emulation using heating actuators are not described in detail, but a list of relevant references is given.
The structure of currents and electric fields in the edge tokamak plasma is analysed for detached regimes of a tokamak. Strong electric fields in the divertor regions and near the X‐point are typical ...for detached regimes. It is shown that the value of the poloidal electric field in the regions with the temperature 1–2 eV is determined by the Spitzer conductivity and parallel currents. The latter are a combination of thermal and Pfirsch–Schlüter (PS) currents. The E × B drifts have a significant impact on the distribution of the plasma in the divertor. Stability of the detached regimes with strong electric fields is also analysed. It has been demonstrated that the so‐called PS instability caused by PS current can develop in the cold low‐temperature regions of the detached divertor.
The study of conditions for obtaining quasi-stationary scenarios in the T-15MD tokamak is performed. Results of simulation and optimization of T-15MD regimes with a fully noninductive current drive ...using NBICD systems with the power of 6–8 MW, ECCD system with the power ~8 MW, and RFCD system with power up to 7–8 MW are presented. It is shown that, at the somewhat reduced value as compared to the basic value of the toroidal magnetic field
B
t
~ 1.5 T in the T-15MD tokamak, discharges can be produced with a fully noninductive current of about 1 MA, plasma temperature of several keV, plasma density of about (3–7) × 10
19
m
–3
, and discharge duration of about 20 s. Such discharges are of interest for further experimental study.
On ADITYA-U tokamak, a spectroscopic diagnostic has been developed to measure the radial profile of visible continuum radiation for determining the plasma effective charge, Zeff, to study the ...impurity transport and MHD driven instabilities. It consists of the collimating lenses, optical fibers, a multi-channel wavelength selection system, and photo multiplier tubes. The optical system allowing continuum radiation measurements around 536 nm (the wavelength selection system) consists of set of lenses, optical fibers and an interference filter with diameter of 5 cm and bandwidth of 3 nm. The spatial profile of radiation with a spatial resolution of ∼ 3 cm has been recorded from eight lines of sight viewing the plasma using an UHV compatible rectangular view port placed on the bottom port of the ADITYA-U tokamak. The centrally peaked spatial profile of visible continuum radiation has been recorded from the ADITYA-U tokamak plasmas. The chord averaged Zeff values estimated from the brightness measured along the central chord fall within 2.5 to 4.1 for the electron densities of 1.0 - 2.2 × 1019 m−3.
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