| 1. |
- Stork, D., et al.
(författare)
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Overview of transport, fast particle and heating and current drive physics using tritium in JET plasmas
- 2005
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Ingår i: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 45:10, s. S181-S194
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Tidskriftsartikel (refereegranskat)abstract
- Results are presented from the JET Trace Tritium Experimental (TTE) campaign using minority tritium (T) plasmas (n(T)/n(D) < 3%). Thermal tritium particle transport coefficients (D-T, nu(T)) are found to exceed neo-classical values in all regimes, except in ELMy H-modes at high densities and in the region of internal transport barriers (ITBs) in reversed shear plasmas. In ELMy H-mode dimensionless parameter scans, at q(95) 2.8 and triangularity delta = 0.2, the T particle transport scales in a gyro-Bohm manner in the inner plasma (r/a < 0.4), whilst the outer plasma particle transport scaling is more Bohm-like. Dimensionless parameter scans show contrasting behaviour for the trace particle confinement (increases with collisionality, nu* and beta) and bulk energy confinement (decreases with nu* and is independent of beta). In an extended ELMy H-mode data set, with rho*, nu*, and q varied but with neo-classical tearing modes (NTMs) either absent or limited to weak, benign core modes (4/3 or above), the multiparameter fit to the normalized diffusion coefficient in the outer plasma (0.65 < r/a < 0.8) gives D-T/B-phi similar to rho*(2.46) nu*(-0.23) beta(-1.01) q(2.03). In hybrid scenarios (q(min) similar to 1, low positive shear, no sawteeth), the T particle confinement is found to scale with increasing triangularity and plasma current. Comparing regimes (ELMy H-mode, ITB plasma and hybrid scenarios) in the outer plasma region, a correlation of high values of D-T with high values Of nu(T) is seen. The normalized diffusion coefficients for the hybrid and ITB scenarios do not fit the scaling derived for ELMy H-modes. The normalized tritium diffusion scales with normalized poloidal Larmor radius (rho(theta)* = q rho*) in a manner close to gyro-Bohm (similar to rho(sigma)*(3)), with an added inverse P dependence. The effects of ELMs, sawteeth and NTMs on the T particle transport are described. Fast-ion confinement in current-hole (CH) plasmas was tested in TTE by tritium neutral beam injection into JET CH plasmas. gamma-rays from the reactions of fusion alpha and beryllium impurities (Be-9(alpha, n gamma)C-12) characterized the fast fusion-alpha population evolution. The gamma-decay times are consistent with classical alpha plus parent fast triton slowing down times (tau(Ts) + tau(alpha s)) for high plasma currents (I-p > 2 MA) and monotonic q-profiles. In CH discharges the gamma-ray emission decay times are much lower than classical (tau(Ts) + tau(alpha s)), indicating alpha confinement degradation, due to the orbit losses and particle orbit drift predicted by a 3-D Fokker-Planck numerical code and modelled using TRANSP.
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| 2. |
- Giroud, C., et al.
(författare)
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Method for experimental determination of Z dependence of impurity transport on JET
- 2007
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 47:4, s. 313-330
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Tidskriftsartikel (refereegranskat)abstract
- The prediction of impurity peaking in future fusion devices such as ITER necessitates the study of the dependence on Z of the impurity transport in present devices. In this paper we describe a novel technique to determine the transport of impurities with different atomic numbers independently. A technique has been developed that allows simultaneously the measurement of the transport of Ne and Ar in the same discharge while minimizing the systematic errors in the spectroscopic measurements. The reproduction of the charge-exchange measured densities, absolute vaccum ultra-violet line intensities and absolute soft x-ray intensity is achieved in an impurity transport simulation. The method used to estimate the errors on the transport coefficients of neon (Ne) and argon (Ar) is presented. In the plasma region where the diffusion and convection coefficients are determined for hybrid discharges, the transport of Ne and Ar is observed to exceed neoclassical predictions. In the same regions, the diffusion coefficients of both impurities are similar. The convection coefficients are also comparable for Ne and Ar. The peaking of Ne and Ar density profiles are comparable during the period where the intermittent slow reconnecting n = 1 mode is stable in these hybrid discharges.
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| 5. |
- von Hellermann, M G, et al.
(författare)
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Complex spectra in fusion plasmas
- 2005
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Ingår i: Physica Scripta. - 0031-8949. ; T120, s. 19-29
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Tidskriftsartikel (refereegranskat)abstract
- The need for quantitative evaluation of complex line emission spectra as observed in hot fusion plasmas initiated a challenging development of sophisticated interpretation tools based on integrating advanced atomic modelling with detailed treatment of the plasma environment. The successful merging of the two worlds has led to routine diagnostic procedures which have contributed enormously to the understanding of underlying plasma processes and also to a wide acceptance of spectroscopy as a reliable diagnostic method. In this paper three characteristic types of spectra of current and continuing interest are presented. The first is that of medium/ heavy species with many ionisation stages revealed in survey VUV and XUV spectra. Such species occur as control gases, as wall materials, as ablated heavy species and possible as layered wall dopants for monitoring erosion. The spectra are complex with line- like and quasi-continuum regions and are amenable to advanced 'pattern recognition' methods. The second type is of few electron, highly ionised systems observed as line-of-sight integrated passive emission spectra in the soft X-ray region. They are analysed successfully in terms of plasma parameters through matching of observation with predicted synthetic spectra. Examples used here include highly resolved helium-like emission spectra of argon, iron and titanium observed on the tokamaks TEXTOR and Tore Supra. The third type, and the emphasis of this work, comprises spectra linked to active beam spectroscopy, that is, charge exchange recombination spectroscopy (CXRS) and beam emission spectroscopy ( BES). In this case, a complex spectrum is again composed of a ( usually) dominating active spectrum and an underlying passive emission spectrum. Its analysis requires modelling of both active and passive features. Examples used here are from the CXRS diagnostic at JET and TEXTOR. They display characteristic features of the main light impurity ions (C+6, He+2, N+7, Ne+10 and Ar+18), as well as that of the bulk plasma ions, H+, D+ and T+. A main conclusion is that spectral complexity is not necessarily negative, but that 'complex structures' can provide a rich source of information on the plasma and its parameters - provided it is matched with integrated analysis - and that the methods can have universal applicability. In the present preparatory phase of the next generation fusion experiment ITER ( International Thermonuclear Experimental Reactor) the concepts and expectations of complex spectra and integrated data analysis play an important role in the design and optimisation procedure of the ITER diagnostic assembly.
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| 6. |
- Hobbs, David, et al.
(författare)
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Gaia and the Astrometric Global Iterative Solution
- 2008
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Ingår i: Proceedings of IInternational Astronomical Union, IAU Symposium. ; 248, s. 119-120
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Konferensbidrag (refereegranskat)abstract
- Gaia is an ESA space astrometry mission due for launch in 2011-12. We describe part of the work carried out in the Gaia Data Processing and Analysis Consortium, namely the Astrometric Global Iterative Solution (AGIS) currently being implemented at the European Space Astronomy Center (ESAC) in Spain and largely based on algorithms developed at Lund Observatory. Some provisional results based on simulated observations of one million stars are presented, demonstrating convergence at microarcsec level independent of starting conditions.
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| 7. |
- Murari, A., et al.
(författare)
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New diagnostic techniques and technologies at JET (invited)
- 2006
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 77:10
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Tidskriftsartikel (refereegranskat)abstract
- The European Fusion Development Agreement's mission for JET is the development of ITER scenarios exploiting the specific properties of the device. This task requires significant improvements in the measuring techniques. The most innovative diagnostic upgrades are in the fields of edge measurements, detection of fast magnetohydrodynamics modes and burning plasma diagnostics. The importance of plasma-wall interactions, and, in particular, the issue of tritium inventory promoted the development of the quartz microbalance, a detector with improved time resolution to measure material redeposition in the remote areas of the inner divertor. Measurement of Alfven cascades with unprecedented spectral resolution, reaching a toroidal n number of up to 16, was obtained using an O-mode microwave reflectometer as an interferometer. For the diagnosis of the fusion products, a new approach is being developed to measure the He ash based on double charge exchange between thermalized particles and neutrals from JET beams. There have been several upgrades of the neutron diagnostic systems, one of which, the new time of flight neutron spectrometer designed for high counting rates is described.
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