28,597 research outputs found
Measurement of the plasma edge profiles using the combined probe on W7-X
No full textWendelstein 7-X (W7-X), started operation in December 2015 with a limiter configuration. In conjunction with the multi-purpose manipulator, a carrier for fast reciprocating probe systems, the combined probe has been installed. This combined probe is able to measure the local electron temperatures and densities, magnetic field, the electric field and the plasma flow. These parameters are very useful in ascertaining the edge plasma perfomance. In addition, the field line tracing feature of the W7-X webservices was used to calculate the connection length along the path of the probe, for each configuration
Spectroscopic camera system at Wendelstein 7-X
No full textA network of spectroscopic cameras was installed and successfully operated during the entire operation phase 1 of the optimized stellarator, Wendelstein 7-X. This diagnostic system enabled spatially resolved measurements of photon fluxes at specific wavelengths. Narrow band pass filters in the optical path allowed for targeted photon flux measurements of various spectral lines, specifically for the main ion species, hydrogen, and the primary impurity, carbon. The cameras were arranged in a stellarator-symmetric configuration, with one camera assembly per half-module. Each camera was equipped with a 135 ° ultra-wide field-of-view lens centered on the divertor, enabling comprehensive observation of the entire divertor unit, including the baffle and most of the surrounding heat shield. This configuration achieved coverage of 56 % of all plasma-facing surfaces at W7-X, providing a spatial resolution up to 1.4 pixel/cm at a frame rate of 25 Hz. This diagnostic system supports a wide range of applications, from studies of ionizing particle fluxes and wall recycling to investigations of plasma radiation and detachment, edge impurity sources, and their distribution. This paper details the diagnostic system's observation geometry, measurement principles, calibration processes, inter-diagnostic comparisons, synthetic diagnostic modeling, and plans for further development
Large scale CW ECRH systems: Meeting a challenge
No full textElectron Cyclotron Resonance Heating (ECRH) systems for next step-fusion devices like W7-X and ITER operate in CW-mode and provide a large flexibility to comply with various physics demands such as plasma start-up, heating and current drive, as well as configuration and MHD control. The request for many different sophisticated applications results in a growing complexity of the systems. This is in conflict with the request for high availability, reliability, and maintainability, which arises from DEMO demands. 'Advanced' ECRH-components must, therefore, comply with both the complex physics demands and operational robustness and reliability. The W7-X ECRH system is the first CW facility of an ITER relevant size and is used as a test bed for such components. Results on improvements of gyrotrons, transmission components and launchers are presented together with proposals for future developments. © 2011 American Institute of Physics
Study of radial heat transport in W7-X using the transfer entropy
No full textAutor colectivo: W7-X TeamIn this work, we analyze data obtained using the electron cyclotron emission radiometer at the Wendelstein 7-X stellarator using a relatively new technique: the transfer entropy. Thus, we detect the propagation of information and find that it occurs in a stepwise fashion: we observe both 'trapping zones' and radial 'jumps', when the information is apparently skipping over intermediate positions. Using scans of the rotational transform, we observe that the 'trapping zones' appear to be associated with rational surfaces. Power scan experiments show that these 'jumps' increase in importance when power is increased, thus enhancing the effective diffusivity. The observations are interpreted in terms of a resistive magneto-hydrodynamic model, which displays behavior similar to the experimental results. The 'trapping zones' are explained in terms of zonal flows associated with rational surfaces, while the 'jumps' are ascribed to mode coupling effects, i.e. the transmission of turbulent energy via the magnetic field
Equilibrium effects on the structure of island divertor and its impact on the divertor heat flux distribution in Wendelstein 7-X
No full textAbstract
To support the planning of high-performance long-pulse plasma operation for W7-X, the role of equilibrium effects for the structure of island divertor and its profound impacts on the divertor heat flux distribution have been investigated. Finite-beta full-field three-dimensional equilibria for the four most important configurations of W7-X (‘standard’, ‘high-mirror’, ‘high-iota’ and ‘low-iota’) were obtained with the HINT code. Equilibrium calculations show a strong dependence of the edge stochastization on the magnetic configurations. Parameterization to estimate equilibrium effects on edge stochastization and plasma shape was attempted for individual functions. The results indicate that a more stochastic boundary can be attained with increasing plasma beta, except for the low-iota configuration. According to fully diffusive heat-load estimations, it turns out that equilibrium effects are beneficial for spreading the heat flux on the divertor target. The interactions of the beta effects with effects driven by the toroidal plasma current are also analyzed for the standard configuration. Infrared camera measurements confirm the predictions concerning global heat load distributions.</jats:p
Experimental investigation of the ECRH stray radiation during the start-up phase in Wendelstein 7-X
No full textElectron cyclotron resonance heating (ECRH) is the main heating mechanism in the Wendelstein 7-X stellarator (W7-X). W7-X is equipped with five absolutely calibrated sniffer probes that are installed in each of the five modules of the device. The sniffer probes monitor energy flux of unabsorbed ECRH radiation in the device and interlocks are fed with the sniffer probe signals. The stray radiation level in the device changes significantly during the start-up phase: Plasma is a strong microwave absorber and during its formation the stray radiation level in sniffer probes reduces by more than 95%. In this paper, we discuss the influence of neutral gas pressure and gyrotron power on plasma breakdown processes
Advanced electron cyclotron heating and current drive experiments on the stellarator Wendelstein 7-X
No full textDuring the first operational phase (OP 1.1) of Wendelstein 7-X (W7-X) electron cyclotron resonance heating (ECRH) was the exclusive heating method and provided plasma start-up, wall conditioning, heating and current drive. Six gyrotrons were commissioned for OP1.1 and used in parallel for plasma operation with a power of up to 4.3 MW. During standard X2-heating the spatially localized power deposition with high power density allowed controlling the radial profiles of the electron temperature and the rotational transform. Even though W7-X was not fully equipped with first wall tiles and operated with a graphite limiter instead of a divertor, electron densities of n e > 3·1019 m-3 could be achieved at electron temperatures of several keV and ion temperatures above 2 keV. These plasma parameters allowed the first demonstration of a multipath O2-heating scenario, which is envisaged for safe operation near the X-cutoff-density of 1.2·1020 m-3 after full commissioning of the ECRH system in the next operation phase OP1.2
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