1,721,460 research outputs found
Neutron spectra unfolding with minimum fisher regularisation
No full textDuring past experimental campaigns at JET, the NE213 liquid scintillator proved to be a valid diagnostic tool for spectral measurements of fusion neutrons emitted from the plasma. The scintillator response function to neutrons is derived from theoretical estimation combined with measurements at an accelerator-based neutron source. The spectrum unfolding poses an illconditioned inversion problem similar to tomographic reconstruction. Minimum Fisher Regularisation (MFR) is one of the established methods in plasma 2D tomography, providing a rapid and robust tool for sparse data inversion without special a priori assumptions. In neutron analyses at JET, the MFR has been applied both in tomography (see contribution by G. Bonheure) and in unfolding the NE213 spectra, where good agreement with results of the standard Maximum Entropy unfolding procedure (MAXED) was demonstrated. This contribution is focussed on further progress in the MFR application to the unfolding of NE213 spectra. In particular, the L-curve maximum curvature optimisation was implemented which gives MFR the full independence required for automated operation. New results are presented in comparison with the MAXED analyses. The differences between the data and the retrofit of the unfolded spectra are studied and the MFR potential for future applications is outlined. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence
High resolution neutron spectrometry with liquid scintillation detectors for fusion applications
No full textOrganic liquid scintillation detectors, e.g. NE213, EJ-301 or BC501A, are routinely used as high resolution neutron spectrometers in many nuclear experiments. The neutron energy spectrum can be reliably determined from the pulse height spectrum provided the response function of the detector is well determined, counting statistics is sufficient, a suitable unfolding method is applied and care is taken to ensure the gain stability of the system during the measurement. The Physikalisch-Technische Bundesanstalt (PTB) has many years of experience with the development, detailed characterization and use of liquid scintillation detectors. Recent work done at PTB in collaboration with ENEA and EFDA-JET concerning the use of liquid scintillation detectors as neutron diagnostic instruments in fusion experiments is discussed. An NE213 liquid scintillator system has been carefully characterized and successfully used in a series of measurements at the Joint European Torus (JET). We describe the improvements that were made to the system to meet the challenging measurement conditions at JET, as well as the processes used to calibrate and characterize the system. For the determination of the neutron light output function and for a comparison of experimentally determined response functions with those calculated with Monte Carlo techniques, measurements have been performed at the PTB facility in mono-energetic neutron reference fields and in fields with a broad energy distribution applying time of flight spectrometry. Selected examples of measured neutron spectra are discussed in terms of energy resolution and compared to the expected neutron spectra, both for measurements at the PTB accelerator and at JET. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence
Neutron diagnostics for reactor scale fusion experiments: A review of JET systems
No full textFusion is preparing for and moving towards reactor scale plasma experiments. The ITER project requires stepping up the capabilities of neutron measurement systems because in a fusion reactor, measurements of neutron yield and of fusion power and power density are essential. Fast neutron measurement systems for fusion applications include neutronux measurement systems, neutron imaging systems and neutron spectrometers. The JET tokamak is the most suitable test bed for the development of these systems due to its plasma parameters and unique tritium operation capability. Existing systems include 2 neutron cameras composed of multi-collimator arrays and which allow the development of more advanced applications such as 2-D neutron imaging for the study of critical physical phenomena. The spectral width of the neutron emission should be a reliable indicator of ion temperature in a reactor grade plasma. Therefore, three types of neutron spectrometers are currently being developed. The different approaches, methods and calibration techniques are summarised. Finally, since the needs for development of robust and proved neutron measurement systems for ITER are increasingly recognised, JET has now started a series of interesting technological developments in variouselds including new radiation hard detectors, new electronics and data acquisition. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence
A digital data acquisition system optimized for spectrometry with liquid scintillation detectors
No full textThe prototype of a new concept FPGA-based digital acquisition board has been developed for application with scintillation detectors. The board performs digitisation of pulses at 200 MSamples/s with 14-bit resolution. A Dynamic Windows Data Acquisition (DWDA) method is used such that data sampling occurs only when pulses are present and for a time window depending on the width of each pulse. This allows to reduce the amount of stored data and, at the same time, to handle count rates up to the MHz range. Peak identification, baseline correction, pile-up removal, neutron/ ray separation and pulse height analysis are performed by means of a LabVIEWTM program. We show the results of measurements carried out with an NE213 liquid scintillation detector at the PTB (Physikalisch-Technische Bundesanstalt) accelerator facility in Braunschweig (Germany) both with 2.5 MeV and 14 MeV neutrons. The measurements have been performed at different source to detector distances as well as various detection angles. In the digital branch of the acquisition, the pulses have been stored on disk and analysed after the experiment. The comparison between the PTB standard analogue pulse processing system and the new digital system is presented and discussed, in particular in terms of energy resolution, dependence of the pulse height spectra on different total count rates, system stability with time, pile-up rejection and neutron/-ray separation capability. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence
Digital Pulse Shape Discrimination in Organic Scintillators for Fusion Applications
No full textStilbene and NE213 organic scintillators are commonly used for neutron and gamma-ray detection in mixed n/gamma fields due to their pulse shape discrimination properties. A system for n/gamma digital pulse shape discrimination (DPSD) and simultaneous pulse height analysis using a commercial 12-bit 200 MHz transient recorder is presented. The results of measurements performed on the fusion experiment FTU (Frascati Tokamak Upgrade) are described. The importance of DPSD for fusion applications and its advantages with respect to analog PSD are analyze
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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