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- Lamalle, P. U., et al.
(författare)
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Expanding the operating space of ICRF on JET with a view to ITER
- 2006
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 46:2, s. 391-400
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on ITER-relevant ion cyclotron resonance frequency (ICRF) physics investigated on JET in 2003 and early 2004. Minority heating of helium three in hydrogen plasmas-(He-3)H-was systematically explored by varying the 3 He concentration and the toroidal phasing of the antenna arrays. The best heating performance (a maximum electron temperature of 6.2 keV with 5 MW of ICRF power) was obtained with a preferential wave launch in the direction of the plasma current. A clear experimental demonstration was made of the sharp and reproducible transition to the mode conversion heating regime when the 3 He concentration increased above similar to 2%. In the latter regime the best heating performance (a maximum electron temperature of 8 keV with 5 MW of ICRF power) was achieved with dipole array phasing, i.e. a symmetric antenna power spectrum. Minority heating of deuterium in hydrogen plasmas-(D)H-was also investigated but was found inaccessible because this scenario is too sensitive to impurity ions with Z/A = 1/2 such as C6+, small amounts of which directly lead into the mode conversion regime. Minority heating of up to 3% of tritium in deuterium plasmas was systematically investigated during the JET trace tritium experimental campaign (TTE). This required operating JET at its highest possible magnetic field (3.9 to 4 T) and the ICRF system at its lowest frequency (23 MHz). The interest of this scenario for ICRF heating at these low concentrations and its efficiency at boosting the suprathermal neutron yield were confirmed, and the measured neutron and gammay ray spectra permit interesting comparisons with advanced ICRF code simulations. Investigations of finite Larmor radius effects on the RF-induced high-energy tails during second harmonic (omega = 2 omega(c)) heating of a hydrogen minority in D plasmas clearly demonstrated a strong decrease in the RF diffusion coefficient at proton energies similar to 1 MeV in agreement with theoretical expectations. Fast wave heating and current drive experiments in deuterium plasmas showed effective direct electron heating with dipole phasing of the antennas, but only small changes of the central plasma current density were observed with the directive phasings, in particular at low single pass damping. New investigations of the heating efficiency of ICRF antennas confirmed its strong dependence on the parallel wavenumber spectrum. Advances in topics of a more technological nature are also summarized: ELM studies using fast RF measurements, the successful experimental demonstration of a new ELM-tolerant antenna matching scheme and technical enhancements planned on the JET ICRF system for 2006, they being equally strongly driven by the preparation for ITER.
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- 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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| 8. |
- Castor, Martin, 1972-
(författare)
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The use of structural equation modeling to describe the effect of operator functional state on air-to-air engagement outcomes
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Computational evidence of the operative usefulness of a new system is crucial in large system development processes concerning billions of euros or dollars. Although it is obvious that the human often is the most important and critical component of many systems, it has often been hard for Human Factors researchers to express human aspects in a computational and strict way. The thesis describes, through data based statistical modeling, how the concepts or constructs of sensor effectiveness, usability of information, mental workload, situation awareness and teamwork relates to each other and to the operative performance in a fourship of fighter pilots. Through the use of structural equation modeling, ad modum LISREL, a statistical model that describes how the operators’ functional state mediates the effects between technical system oriented variables, was developed.The constructs used in the modeling process have received widespread scientific and operational attention. They have also been identified as multi-dimensional. Many different ways of measuring them have been developed in the scientific community, and the thesis focuses on the next step, i.e. how do these higher order constructs relate to each other in something as multi-dimensional as human activity in real situations?A comprehensive human factors related dataset was collected in a large simulation based acquisition study that examined the requirements and properties of aircraft radar systems. The dataset contains 308 simulated engagements with data from four pilots each, i.e. 1232 cases in a database with 24 variables, generated by 37 pilots. The collected data and the resulting models thus summarizes more than 700 hours of experienced pilots’ complex behavior in an operationally valid environment, and in a way that is of theoretical interest as well as of importance in system development processes. The data thus comes from a real world study of complex processes in a dynamic context, although from a simulator. The thesis is a case example of modern ecologically valid experimental psychology. The data collection does not represent a classical experimental setup, but instead demonstrates methodological needs and considerations for human factors practitioners when working in system development studies. The fact that parts of the used data are classified has not affected the models and scientific conclusions, although the practical findings have been partly circumscribed in the presentation.As a result of the statistical modeling effort, a structural equation model of how the chosen constructs relate to each other, and mediate effects between technical measures by a model of the operator, is proposed. Simplicity of the model was the goal, and based on former experiences and findings, a simplex structure was hypothesized. The final model shows that the covariances between the 24 measures can be explained by a quasi-simplex structure of seven factors.
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