2,360 research outputs found
A quasi-isodynamic configuration with good confinement of fast ions at low plasma
A new quasi-isodynamic stellarator configuration optimized for the
confinement of energetic ions at low plasma is obtained. The numerical
optimization is carried out using the STELLOPT suite of codes. New proxies to
measure closeness to quasi-isodynamicity and quality of fast ion confinement
have been included. The new configuration has poloidally closed contours of
magnetic field strength, low magnetic shear and a rotational transform profile
allowing an island divertor. It shows ideal and ballooning magnetohydrodynamic
stability up to , reduced effective ripple, with in the plasma core. Even at low , the configuration approximately
satisfies the maximum- property, and the confinement of fast ions is good at
and becomes excellent at reactor values, . An
evaluation of the neoclassical mono-energetic coefficient supports the
expectation of a reduced bootstrap current for plasmas confined in
quasi-isodynamic configurations. A set of filamentary coils that preserve the
good confinement of fast ions in the core is presented.Comment: 21 pages, 16 figure
Influence of Zn excess on compositional, structural and vibrational properties of Cu2ZnSn0.5Ge0.5Se4 thin films and their effect on solar cell efficiency
This Accepted Manuscript will be available for reuse under a CC BY-NC-ND licence after 24 months of embargo periodThe effect of Zn content on compositional, structural and vibrational properties of Cu2ZnSn1-xGexSe4 (CZTGSe, x ~ 0.5) thin films is studied. Kesterite layer is deposited by co-evaporation onto 5 × 5 cm2 Mo/SLG substrate followed by a thermal treatment at maximum temperature of 480 °C, obtaining areas with different composition and morphology which are due to the sample position in the co-evaporation system and to the non-uniform temperature distribution across the substrate. Kesterite layers with higher Zn amounts are characterized by lower Cu and Ge contents; however, a uniform Ge distribution through the absorber layer is detected in all cases. The excess Zn concentration leads to the formation of ZnSe secondary phase on the surface and in the bulk of the absorber as determined by Raman spectroscopy. When higher Ge content and no ZnSe are present in the absorber layer, a compact structure is formed with larger grain size of kesterite. This effect could explain the higher Voc of the solar cell. The Zn content does not affect the bandgap energy significantly (Eg near 1.3 eV), although the observed effect of Zn excess in CZTGSe results in a decreased device performance from 6.4 to 4.2%. This investigation reveals the importance of the control of the off-stoichiometric CZTGSe composition during the deposition process to enhance solar cells propertiesThis work was supported by Spanish Ministry of Science, Innovation and Universities Project WINCOST (ENE2016-80788-C5-2-R) and European Project INFINITE CELL (H2020-MSCA-RISE-2017-777968). ARP also acknowledges financial support from Community of Madrid within Youth Employment Program (PEJD-2017-PRE/IND-4062). MG acknowledges the financial support from ACCIÓ-Generalitat de Catalunya within the TECNIOspring Plus fellowship (TECSPR18-1-0048
Comparison of local and global gyrokinetic calculations of collisionless zonal flow damping in quasi-symmetric stellarators
The linear collisionless damping of zonal flows is calculated for
quasi-symmetric stellarator equilibria in flux-tube, flux-surface, and
full-volume geometry. Equilibria are studied from the quasi-helical symmetry
configuration of the Helically Symmetric eXperiment (HSX), a broken symmetry
configuration of HSX, and the quasi-axial symmetry geometry of the National
Compact Stellarator eXperiment (NCSX). Zonal flow oscillations and long-time
damping affect the zonal flow evolution, and the zonal flow residual goes to
zero for small radial wavenumber. The oscillation frequency and damping rate
depend on the bounce-averaged radial particle drift in accordance with theory.
While each flux tube on a flux surface is unique, several different flux tubes
in HSX or NCSX can reproduce the zonal flow damping from a flux-surface
calculation given an adequate parallel extent. The flux-surface or flux-tube
calculations can accurately reproduce the full-volume long-time residual for
moderate , but the oscillation and damping time scales are longer in local
representations, particularly for small approaching the system size.Comment: The following article has been accepted by Physics of Plasmas. After
it is published, it will be found at https://aip.scitation.org/journal/php.
33 pages, 18 figure
Oscillatory relaxation of zonal flows in a multi-species stellarator plasma
The low frequency oscillatory relaxation of zonal potential perturbations is
studied numerically in the TJ-II stellarator (where it was experimentally
detected for the first time). It is studied in full global gyrokinetic
simulations of multi-species plasmas. The oscillation frequency obtained is
compared with predictions based on single-species simulations using simplified
analytical relations. It is shown that the frequency of this oscillation for a
multi-species plasma can be accurately obtained from single-species
calculations using extrapolation formulas. The damping of the oscillation and
the influence of the different inter-species collisions is studied in detail.
It is concluded that taking into account multiple kinetic ions and electrons
with impurity concentrations realistic for TJ-II plasmas allows to account for
the values of frequency and damping rate in zonal flows relaxations observed
experimentally.Comment: 11 figures, 22 page
Comparison of local and global gyrokinetic calculations of collisionless zonal flow damping in quasi-symmetric stellarators
The linear collisionless damping of zonal flows is calculated for quasi-symmetric stellarator equilibria in flux-tube, flux-surface, and full-volume geometry. Equilibria are studied from the quasi-helical symmetry configuration of the Helically Symmetric eXperiment (HSX), a broken symmetry configuration of HSX, and the quasi-axial symmetry geometry of the National Compact Stellarator eXperiment (NCSX). Zonal flow oscillations and long-time damping affect the zonal flow evolution, and the zonal flow residual goes to zero for small radial wavenumber. The oscillation frequency and damping rate depend on the bounce-averaged radial particle drift in accordance with theory. While each flux tube on a flux surface is unique, several different flux tubes in HSX or NCSX can reproduce the zonal flow damping from a flux-surface calculation given an adequate parallel extent. The flux-surface or flux-tube calculations can accurately reproduce the full-volume long-time residual for moderate kx, but the oscillation and damping time scales are longer in local representations, particularly for small kx approaching the system size.</p
Effect of pig slaughter weight on chemical and sensory characteristics of Teruel dry-cured ham
A preliminary study was carried out with 36 barrows to investigate the effect of slaughter weight (SW; 120, 130 and 140 kg) on chemical, instrumental and sensory characteristics of Teruel drycured ham. The intramuscular fat content tended to increase and salt, potassium nitrate and sodium nitrite contents decreased as SW increased. The panelists detected wider subcutaneous fat and lower cured colour, saltiness, hardness and fibrousness in hams from heavier pigs but no difference was observed on overall quality assessment. In conclusion, pig SW affected some chemical and sensory traits of dry-cured ham, which contributes to increase the heterogeneity
Diseño y realización de un programa de prácticas sobre comportamiento, adecuado al tema de etología
- …