| 1. |
- Diakaki, M., et al.
(author)
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Towards the high-accuracy determination of the 238U fission cross section at the threshold region at CERN -€“ n_TOF
- 2016
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In: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X.
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Conference paper (peer-reviewed)abstract
- The U-238 fission cross section is an international standard beyond 2 MeV where the fission plateau starts. However, due to its importance in fission reactors, this cross-section should be very accurately known also in the threshold region below 2 MeV. The U-238 fission cross section has been measured relative to the U-235 fission cross section at CERN - n_TOF with different detection systems. These datasets have been collected and suitably combined to increase the counting statistics in the threshold region from about 300 keV up to 3 MeV. The results are compared with other experimental data, evaluated libraries, and the IAEA standards.
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| 2. |
- Paradela, C., et al.
(author)
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High-accuracy determination of the 238U/235U fission cross section ratio up to ~1 GeV at n_TOF at CERN
- 2015
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In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 91, s. 024602-
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Journal article (peer-reviewed)abstract
- The U238 to U235 fission cross section ratio has been determined at n_TOF up to ≈1 GeV, with two different detection systems, in different geometrical configurations. A total of four datasets has been collected and compared. They are all consistent to each other within the relative systematic uncertainty of 3–4%. The data collected at n_TOF have been suitably combined to yield a unique fission cross section ratio as a function of neutron energy. The result confirms current evaluations up to 200 MeV. Good agreement is also observed with theoretical calculations based on the INCL++/Gemini++ combination up to the highest measured energy. The n_TOF results may help solve a long-standing discrepancy between the two most important experimental datasets available so far above 20 MeV, while extending the neutron energy range for the first time up to ≈1 GeV.
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| 3. |
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| 4. |
- Leal-Cidoncha, E., et al.
(author)
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Fission Fragment Angular Distribution measurements of 235U and 238U at CERN n_TOF facility
- 2016
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In: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X.
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Conference paper (peer-reviewed)abstract
- Neutron-induced fission cross sections of U-238 and U-235 are used as standards in the fast neutron region up to 200 MeV. A high accuracy of the standards is relevant to experimentally determine other neutron reaction cross sections. Therefore, the detection efficiency should be corrected by using the angular distribution of the fission fragments (FFAD), which are barely known above 20 MeV. In addition, the angular distribution of the fragments produced in the fission of highly excited and deformed nuclei is an important observable to investigate the nuclear fission process. In order to measure the FFAD of neutron-induced reactions, a fission detection setup based on parallel-plate avalanche counters (PPACs) has been developed and successfully used at the CERN-n_TOF facility. In this work, we present the preliminary results on the analysis of new U-235(n,f) and U-238(n,f) data in the extended energy range up to 200 MeV compared to the existing experimental data.
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| 5. |
- Del Dotto, V., et al.
(author)
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SSBP1 mutations cause mtDNA depletion underlying a complex optic atrophy disorder
- 2020
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In: Journal of Clinical Investigation. - : American Society for Clinical Investigation. - 0021-9738 .- 1558-8238. ; 130:1, s. 108-125
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Journal article (peer-reviewed)abstract
- Inherited optic neuropathies include complex phenotypes, mostly driven by mitochondrial dysfunction. We report an optic atrophy spectrum disorder, including retinal macular dystrophy and kidney insufficiency leading to transplantation, associated with mitochondrial DNA (mtDNA) depletion without accumulation of multiple deletions. By whole-exome sequencing, we identified mutations affecting the mitochondrial single-strand binding protein (SSBP1) in 4 families with dominant and 1 with recessive inheritance. We show that SSBP1 mutations in patient-derived fibroblasts variably affect the amount of SSBP1 protein and alter multimer formation, but not the binding to ssDNA. SSBP1 mutations impaired mtDNA, nucleoids, and 7S-DNA amounts as well as mtDNA replication, affecting replisome machinery. The variable mtDNA depletion in cells was reflected in severity of mitochondrial dysfunction, including respiratory efficiency, OXPHOS subunits, and complex amount and assembly. mtDNA depletion and cytochrome c oxidase-negative cells were found ex vivo in biopsies of affected tissues, such as kidney and skeletal muscle. Reduced efficiency of mtDNA replication was also reproduced in vitro, confirming the pathogenic mechanism. Furthermore, ssbp1 suppression in zebrafish induced signs of nephropathy and reduced optic nerve size, the latter phenotype complemented by WT mRNA but not by SSBP1 mutant transcripts. This previously unrecognized disease of mtDNA maintenance implicates SSBP1 mutations as a cause of human pathology.
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| 6. |
- Mantsinen, M. J., et al.
(author)
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Localized bulk electron heating with ICRF mode conversion in the JET tokamak
- 2004
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In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 44:1, s. 33-46
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Journal article (peer-reviewed)abstract
- Ion cyclotron resonance frequencies (ICRF) mode conversion has been developed for localized on-axis and off-axis bulk electron heating on the JET tokamak. The fast magnetosonic waves launched from the low-field side ICRF antennas are mode-converted to short-wavelength waves on the high-field side of the He-3 ion cyclotron resonance layer in D and He-4 plasmas and subsequently damped on the bulk electrons. The resulting electron power deposition, measured using ICRF power modulation, is narrow with a typical full-width at half-maximum of approximate to30 cm (i.e. about 30% of the minor radius) and the total deposited power to electrons comprises at least up to 80% of the applied ICRF power. The ICRF mode conversion power deposition has been kept constant using He-3 bleed throughout the ICRF phase with a typical duration of 4-6 s, i.e. 15-40 energy confinement times. Using waves propagating in the counter-current direction minimizes competing ion damping in the presence of co-injected deuterium beam ions.
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| 7. |
- Noterdaeme, J. M., et al.
(author)
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Heating, current drive and energetic particle studies on JET in preparation of ITER operation
- 2003
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In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 43:3, s. 202-209
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Journal article (peer-reviewed)abstract
- This paper summarizes the recent work on JET in the three areas of heating, current drive and energetic particles. The achievements have extended the possibilities of JET, have a direct connection to ITER operation and provide new and interesting physics. Toroidal rotation profiles of plasmas heated far off axis with little or no refuelling or momentum input are hollow with only small differences on whether the power deposition is located on the low field side or on the high field side. With LH current drive the magnetic shear was varied from slightly positive to negative. The improved coupling (through the use of plasma shaping and CD4) allowed up to 3.4 MW of PLH in internal transport barrier (ITB) plasmas with more than 15 MW of combined NBI and ICRF heating. The q-profile with negative magnetic shear and the ITB could be maintained for the duration of the high heating pulse (8 s). Fast ions have been produced in JET with ICRF to simulate alpha particles: by using third harmonic He-4 heating, beam injected He-4 at 120 kV were accelerated to energies above 2 MeV taking advantage of the unique capability of JET to use NBI with 4 He and to confine MeV class ions. ICRF heating was used to replicate the dynamics of alpha heating and the control of an equivalent Q = 10 `burn' was simulated.
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| 8. |
- Noterdaeme, J. M., et al.
(author)
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Spatially resolved toroidal plasma rotation with ICRF on JET
- 2003
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In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 43:4, s. 274-289
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Journal article (peer-reviewed)abstract
- Plasmas heated by ICRF only in the JET tokamak show distinct structures in the toroidal rotation profile, with regions where domega/dr > 0 when the minority cyclotron resonance layer is far off-axis. The rotation is dominantly co-current with a clear off-axis maximum. There is only a slight difference between a high-field side (HFS) or a low-field side position of this resonance layer: the off-axis maximum in the rotation profile is modestly higher for the HFS position. This is in contrast to the predictions of theories that rely mainly on the effects arising from ICRF-driven fast ions to account for ICRF-induced plasma rotation. The differences due to the direction of the antenna spectrum (co- or counter-) are small. A more central deposition of the ICRF power in L-mode and operation in H-mode both lead to more centrally peaked profiles, both in the co-direction. Strong MHD modes brake the rotation and lead to overall flat rotation profiles.
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| 9. |
- Hellsten, Torbjörn, et al.
(author)
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Fast wave current drive in JET ITB-plasma
- 2005
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In: AIP Conference Proceedings. - : AIP. - 0094-243X. ; , s. 273-278
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Conference paper (peer-reviewed)abstract
- Fast wave current drive has been performed in JET plasmas with internal transport barriers, ITBs, and strongly reversed magnetic shear. Although the current drive efficiency of the power absorbed on the electrons is fairly high, only small effects are seen in the central current density. The main reasons are the parasitic absorption of RF power, the strongly inductive nature of the plasma and the interplay between the fast wave driven current and bootstrap current. The direct electron heating in the FWCD experiments is found to be strongly degraded compared to that with the dipole phasing.
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| 10. |
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| 11. |
- Korsholm, S. B., et al.
(author)
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Development of novel fuel ion ratio diagnostic techniques
- 2010
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In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 81:10, s. 10D323-
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Journal article (peer-reviewed)abstract
- To overcome the challenge of measuring the fuel ion ratio in the core (rho<0.3) of ITER, a coordinated effort aiming at developing diagnostic techniques has been initiated. The investigated techniques are novel uses or further development of existing methods such as charge exchange recombination spectrometry, neutron spectrometry, and collective Thomson scattering. An overview of the work on the three diagnostic techniques is presented.
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| 12. |
- Lamalle, P. U., et al.
(author)
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Expanding the operating space of ICRF on JET with a view to ITER
- 2006
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In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 46:2, s. 391-400
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Journal article (peer-reviewed)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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| 13. |
- Lamalle, P.U, et al.
(author)
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Expanding the operating space of ICRF on JET with a view to ITER
- 2006
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In: Nucl. Fusion. ; 46, s. 391-
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Journal article (peer-reviewed)abstract
- Mercury (Hg) has been used for millennia in many applications, primarily in artisanal mining and as an electrode in the chlor–alkali industry. It is anthropogenically emitted as a pollutant from coal fired power plants and naturally emitted, primarily from volcanoes. Its unique chemical characteristics enable global atmospheric transport and it is deposited after various processes, ultimately ending up in one of its final sinks, such as incorporated into deep sediment or bioaccumulated, primarily in the marine environment. All forms of Hg have been established as toxic, and there have been no noted biological benefits from the metal.Throughout time, there have been notable incidents of Hg intoxication documented, and the negative health effects have been documented to those chronically or acutely exposed. Today, exposure to Hg is largely diet or occupationally dependent, however, many are exposed to Hg from their amalgam fillings. This paper puts a tentative monetary value on Hg polluted food sources in the Arctic, where local, significant pollution sources are limited, and relates this to costs for strategies avoiding Hg pollution and to remediation costs of contaminated sites in Sweden and Japan. The case studies are compiled to help policy makers and the public to evaluate whether the benefits to the global environment from banning Hg and limiting its initial emission outweigh the benefits from its continued use or lack of control of Hg emissions. The cases we studied are relevant for point pollution sources globally and their remediation costs ranged between 2500 and 1.1 million US$ kg−1 Hg isolated from the biosphere. Therefore, regulations discontinuing mercury uses combined with extensive flue gas cleaning for all power plants and waste incinerators is cost effective.
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| 14. |
- Moseev, D., et al.
(author)
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Elevation angle alignment of quasi optical receiver mirrors of collective Thomson scattering diagnostic by sawtooth measurements
- 2012
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In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 83:10
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Journal article (peer-reviewed)abstract
- Localized measurements of the fast ion velocity distribution function and the plasma composition measurements are of significant interest for the fusion community. Collective Thomson scattering (CTS) diagnostics allow such measurements with spatial and temporal resolution. Localized measurements require a good alignment of the optical path in the transmission line. Monitoring the alignment during the experiment greatly benefits the confidence in the CTS measurements. An in situ technique for the assessment of the elevation angle alignment of the receiver is developed. Using the CTS diagnostic on TEXTOR without a source of probing radiation in discharges with sawtooth oscillations, an elevation angle misalignment of 0.9 degrees was found with an accuracy of 0.25 degrees.
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| 15. |
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| 16. |
- Knippenberg, Stefan, et al.
(author)
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Atomistic Picture of Fluorescent Probes with Hydrocarbon Tails in Lipid Bilayer Membranes : An Investigation of Selective Affinities and Fluorescent Anisotropies in Different Environmental Phases
- 2018
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In: Langmuir. - : AMER CHEMICAL SOC. - 0743-7463 .- 1520-5827. ; 34:30, s. 9072-9084
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Journal article (peer-reviewed)abstract
- By reverting to spectroscopy, changes in the biological environment of a fluorescent probe can be monitored and the presence of various phases of the surrounding lipid bilayer membranes can be detected. However, it is currently not always clear in which phase the probe resides. The well-known orange 1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbo-cyanine perchlorate (DiI-C18(5)) fluorophore, for instance, and the new, blue BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivative were experimentally seen to target and highlight identical parts of giant unilamellar vesicles of various compositions, comprising mixtures of dipalmitoylphosphatidylcholine (DPPC), dioleoylphosphatidylcholine (DOPC), sphingomyelin (SM), and cholesterol (Chol). However, it was not clear which of the coexisting membrane phases were visualized (Bacalum et al., Langmuir. 2016, 32, 3495). The present study addresses this issue by utilizing large-scale molecular dynamics simulations and the z-constraint method, which allows evaluating Gibbs free-energy profiles. The current calculations give an indication why, at room temperature, both BODIPY and DiI-C18(5) probes prefer the gel (S-o) phase in DOPC/DPPC (2:3 molar ratio) and the liquid-ordered (L-o) phase in DOPC/SM/Chol (1:2:1 molar ratio) mixtures. This study highlights the important differences in orientation and location and therefore in efficiency between the probes when they are used in fluorescence microscopy to screen various lipid bilayer membrane phases. Dependent on the lipid composition, the angle between the transition-state dipole moments of both probes and the normal to the membrane is found to deviate clearly from 90 degrees. It is seen that the DiI-C18(5) probe is located in the headgroup region of the SM/Chol mixture, in close contact with water molecules. A fluorescence anisotropy study also indicates that DiI-C18(5) gives rise to a distinctive behavior in the SM/Chol membrane compared to the other considered membranes. The latter behavior has not been seen for the studied BODIPY probe, which is located deeper in the membrane.
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| 17. |
- Mayoral, M. L., et al.
(author)
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Hydrogen plasmas with ICRF inverted minority and mode conversion heating regimes in the JET tokamak
- 2006
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In: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 46:7, s. S550-S563
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Journal article (peer-reviewed)abstract
- During the initial operation of the International Thermonuclear Experimental Reactor (ITER), it is envisaged that activation will be minimized by using hydrogen (H) plasmas where the reference ion cyclotron resonance frequency (ICRF) heating scenarios rely on minority species such as helium (He-3) or deuterium (D). This paper firstly describes experiments dedicated to the study of He-3 heating in H plasmas with a sequence of discharges in which 5 MW of ICRF power was reliably coupled and the He-3 concentration, controlled in real-time, was varied from below 1% up to 10%. The minority heating (MH) regime was observed at low concentrations (up to 2%). Energetic tails in the He-3 ion distributions were observed with effective temperatures up to 300 keV and bulk electron temperatures up to 6 keV. At around 2%, a sudden transition was reproducibly observed to the mode conversion regime, in which the ICRF fast wave couples to short wavelength modes, leading to efficient direct electron heating and bulk electron temperatures up to 8 keV. Secondly, experiments performed to study D minority ion heating in H plasmas are presented. This MH scheme proved much more difficult since modest quantities of carbon
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| 18. |
- Mayoral, M L, et al.
(author)
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ICRF heating for the non-activated phase of ITER : From inverted minority to mode conversion regime
- 2005
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In: Radio Frequency Power in Plasmas. ; , s. 122-129
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Conference paper (peer-reviewed)abstract
- In the initial phase of ITER H plasmas will be used in order to avoid activating the machine. The reference ICRF heating scenarios rely on minority species such as Helium (3 He) or deuterium (D). These schemes' distinctive feature comes from the presence of the fast magnetosonic wave ion-ion hybrid resonance/cut-off pair, between the antennas and the minority cyclotron layer. In order to document these unusual heating schemes, ICRF experiments were carried out recently on JET. First, the use of He-3 ions in H plasmas was investigated with a sequence of discharges in which 5 MW of ICRF power was coupled to the plasma and the 3 He concentration was varied from below 1% up to 10%. The inverted minority heating regime was observed at low concentrations (up to similar to 2%). Energetic tails in the 3 He distribution were observed with effective temperatures up to 300 keV and central electron temperatures up to 6 keV. At around 2%, a sudden transition was reproducibly observed to the mode conversion regime, in which the ICRF fast wave couples to short wavelength modes, leading to efficient direct electron heating and central electron temperature up to 8 keV. All these experiments systematically used power modulation techniques to assess the radial profiles of the wave absorption by the electrons. Secondly, experiments to study the ICRF heating of D minority ions in H were performed. This heating scheme proved much more difficult since modest quantities of C6+ impurity, which has the same Z/A ratio than die D minority ions, led us directly into the mode conversion regime. This effect preventing any absorption by D ions at minority cyclotron layer, could make die (D)H scenario not suitable for the non-active phase of ITER.
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| 19. |
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