3,265 research outputs found
The Deuterium Inventory in ASDEX Upgrade
No full textThe deuterium inventory in ASDEX Upgrade was determined by quantitative ion beam analysis techniques and SIMS for different discharge campaigns between the years 2002 and 2005. ASDEX Upgrade was a carbon dominated machine during this phase. Full poloidal sections of the lower and upper divertor tile surfaces, limiter tiles, gaps between divertor tiles, gaps between inner heat shield tiles and samples from remote areas below the roof baffle and in pump ducts were analysed, thus offering an exhaustive survey of all relevant areas in ASDEX Upgrade. Deuterium is mainly trapped on plasma-exposed surfaces of inner divertor tiles, where about 70% of the retained deuterium inventory is found. About 20% of the inventory is retained at or below the divertor roof baffle, and about 10% is observed in other areas, such as the outer divertor and in gaps between tiles. The long term deuterium retention is 3–4% of the total deuterium input. The obtained results are compared with gas balance measurements, and conclusions about tritium retention in ITER are made
Electron cyclotron resonance heating in ASDEX upgrade: Calculation and experimental authentication of the power deposition profile
No full textIn this paper we present global and local studies of the ECRH power deposition in ASDEX Upgrade. It is organized as follows. Section 2 briefly describes ASDEX Upgrade and its ECRH system. Section 3 presents results for beam paths and ECRH power deposition from beam-tracing calculations for typical examples of EC beam launched perpendicularly and obliquely. In Section 4 some theoretical treatments of the problem and the following consequences are reported. The results from slab model approximation and numerical simulations with consequences for the experiment are presented there as well. The experimental results for the ECRH power deposition are given in Section 5. A summary is given in Section 6. (orig.)Available from TIB Hannover: RA 71(4/280) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
The effect of non-axisymmetric wall geometry on 13C transport in ASDEX Upgrade
No full textWe present the first results of 3D simulations of global 13C transport in ASDEX Upgrade (AUG) indicating that the deposition profile of 13C exhibits toroidal asymmetry in the main chamber. In 2007, the migration of carbon in AUG was studied with a methane (13CH4) injection experiment (A. Hakola et al and the ASDEX Upgrade Team 2010 Plasma Phys. Control. Fusion 52 065006). The total amount of deposited 13C was estimated by assuming toroidally symmetric deposition. Remarkably, the total number of deposited atoms was observed to be less than 10% of the number of injected atoms. The experiment has been simulated with the 3D orbit-following Monte Carlo code ASCOT using both a realistic 3D wall geometry of AUG and a 3D magnetic field with toroidal ripple. The simulations indicate that the non-axisymmetric wall geometry causes notable toroidal asymmetry in the deposition profile in the outer (low-field side) midplane region which can provide a partial explanation for the missing carbon inferred from post-mortem analysis of 13C deposition.</p
Disruption Prediction with Adaptive Neural Networks for ASDEX Upgrade
No full textIn this paper, an adaptive neural system has been built to predict the risk of disruption at ASDEX Upgrade.
The system contains a Self Organizing Map, which determines the ‘novelty’ of the input of a Multi Layer
Perceptron predictor module. The answer of the MLP predictor will be inhibited whenever a novel sample
is detected. Furthermore, it is possible that the predictor produces a wrong answer although it is fed with
known samples. In this case, a retraining procedure will be performed to update the MLP predictor in an
incremental fashion using data coming from both the novelty detection, and from wrong predictions. In
particular, a new update is performed whenever a missed alarm is triggered by the predictor.
The performance of the adaptive predictor during the more recent experimental campaigns until
November 2009 has been evaluated
Tungsten redistribution patterns in ASDEX Upgrade
No full textIn ASDEX Upgrade tungsten is used as a high-Z plasma facing material. Its erosion, migration and subsequent deposition have been studied by analysis of a set of customised marker tiles, which was installed in the divertor and at the central column for one experimental campaign. Erosion rates were determined at the central column, which was the main tungsten source in that campaign. Deposition rates were determined at the central column and in the divertor region. The W-deposition in the divertor is strongly correlated to the local strike point exposure time. In contrast to low-Z wall materials, where deposition occurs mainly in the inner divertor, tungsten is found in similar quantities also in the outer divertor. The total amount of tungsten deposited outside the central column is about 40% of the gross W-source at the central column. One possible explanation for the 60% undetected tungsten might be the prompt local redeposition of eroded W atoms
First neutron spectroscopy measurements in the ASDEX Upgrade tokamak
No full textAbstract: A compact neutron spectrometer based on the liquid scintil-lator BC501A has been installed on the ASDEX Upgrade tokamak. The aim is to measure neutron energy distribution functions as footprints of fast ions distribution functions, generated mainly via Neutral Beam Injection (NBI) in present day tokamaks. A flexible and fast software has been developed to perform digital pulse shape separation and to evaluate pulse height spectra. First measurements of count rates and pulse height spectra show a good sig-nal to noise ratio for integration times comparable to the NBI slowing down time and to the energy confinement time. Due to the perpendicular line of sight, D-d fusion with perpendicular NBI is detected more efficiently and the line broadening of the 2.45 MeV neutrons is higher. Ion Cyclotron Reso-nance Heating (ICRH) combined to NBI exhibits a synergy effect, with count rates higher than the sum of the counts due to NBI and ICRH separately. Although the collimator is designed to screen gammas as much as possible, some qualitative gamma analysis is also possible, providing information in case of runaway electrons during disruptions. The experimental campaign for the characterisation of the system (detector + acquisition system) is complete and the determination of the response function is in progress.
Hydrogen Ion Cyclotron Wall Conditioning for Fuel Removal on TEXTOR and ASDEX Upgrade
No full textIon Cyclotron Wall Conditioning (ICWC), applicable in presence of the toroidal magnetic field, is envisaged in ITER to recover from disruptions, leaks and torus vents, for recycling control and for fuel removal. Various experiments on different devices as well as modeling efforts are advancing to consolidate this technique. This contribution focuses on a selection of recent hydrogen ICWC experiments on ASDEX Upgrade and TEXTOR. The ASDEX Upgrade experiment aimed at comparing isotopic exchange efficiencies previously obtained on Carbon devices to the ITER relevant Tungsten wall. The experiment on TEXTOR aimed at assessing the performance of H2-ICWC for codeposited layer removal. The latter being a particular important fuel removal aspect since it is predicted that a major part of tritium in-vessel inventory build-up on ITER will be due to the formation of tritium rich codeposited layers
Carbon erosion and deposition on the ASDEX Upgrade divertor tiles
No full textCarbon deposition and erosion were measured on ASDEX Upgrade divertor tiles and below the roof baffle during the operation period 2002/2003. The inner divertor is a net carbon deposition area, while a large fraction of the outer divertor is erosion dominated and the roof baffle tiles show a complicated distribution of erosion and deposition areas. In total, 43.7 g B + C were redeposited, of which 88% were deposited on tiles and 9% in remote areas (below roof baffle, on vessel wall structures). 0.6 g C was pumped out as volatile hydrocarbon molecules. Carbon sources in the main chamber are too low by a factor of more than ten to explain the observed carbon divertor deposition. Carbon erosion is observed at the outer divertor strike point tiles, but it is arguable if material can be transported from the outer strike point to the inner divertor
Criteria and algorithms for constructing reliable databases for statistical analysis of disruptions at ASDEX Upgrade
No full textThe present understanding of disruption physics has not gone so far as to provide a mathematical model describing the onset of this instability. A disruption prediction system, based on a statistical analysis of the diagnostic signals recorded during the experiments, would allow estimating the probability of a disruption to take place. A crucial point for a good design of such a prediction system is the appropriateness of the data set. This paper reports the details of the database built to train a disruption predictor based on neural networks for ASDEX Upgrade. The criteria of pulses selection, the analyses performed on plasma parameters and the implemented pre-processing algorithms, are described. As an example of application, a short description of the disruption predictor is reported
DIVIMP-B2-EIRENE modelling of 13C migration and deposition in ASDEX-Upgrade L-mode plasmas
No full textCarbon transport and migration were studied experimentally and numerically in a high-density, low-confinement mode plasma in the ASDEX Upgrade tokamak. On the last day of plasma operation of the 2004–2005 experimental campaign, 13CH4 was injected into the vacuum vessel from the low field side midplane. A poloidal set of tiles was subsequently removed and analysed for 13C deposition. In this work the measured deposition profile is interpreted using the impurity transport code DIVIMP. The simulated poloidal distribution of 13C deviates significantly from the measured profile. The simulations indicate that 13C is promptly deposited at the wall in the vicinity of the injection port, and is transported to the low field side divertor plate predominately via the scrape-off layer. The B2-EIRENE plasma solution produce stagnant plasma flow in the main scrape-off layer, in contrast to measurements in ASDEX Upgrade and other tokamaks. This is the likely cause of the discrepancy between the measured and the calculated poloidal distribution of the 13C deposition. Key model parameters of DIVIMP were varied to determine their effect on the simulated deposition profile
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