6,126 research outputs found
Recent ASDEX Upgrade research in support of ITER and DEMO
Recent experiments on the ASDEX Upgrade tokamak aim at improving the physics base for ITER and DEMO to aid the machine
design and prepare efficient operation. Type I edge localized mode (ELM) mitigation using resonant magnetic perturbations
(RMPs) has been shown at low pedestal collisionality (
ν
∗
ped
<
0
.
4
)
. In contrast to the previous high
ν
∗
regime, suppression only
occurs in a narrow RMP spectral window, indicating a resonant process, and a concomitant confinement drop is observed due
to a reduction of pedestal top density and electron temperature. Strong evidence is found for the ion heat flux to be the decisive
element for the L–H power threshold. A physics based scaling of the density at which the minimum
P
LH
occurs indicates that
ITER could take advantage of it to initiate H-mode at lower density than that of the final
Q
=
10 operational point. Core density
fluctuation measurements resolved in radius and wave number show that an increase of
R/L
T
e
introduced by off-axis electron
cyclotron resonance heating (ECRH) mainly increases the large scale fluctuations. The radial variation of the fluctuation level
is in agreement with simulations using the GENE code. Fast particles are shown to undergo classical slowing down in the
absence of large scale magnetohydrodynamic (MHD) events and for low heating power, but show signs of anomalous radial
redistribution at large heating power, consistent with a broadened off-axis neutral beam current drive current profile under these
conditions. Neoclassical tearing mode (NTM) suppression experiments using electron cyclotron current drive (ECCD) with
feedback controlled deposition have allowed to test several control strategies for ITER, including automated control of (3,2) and
(2,1) NTMs during a single discharge. Disruption mitigation studies using massive gas injection (MGI) can show an increased
fuelling efficiency with high field side injection, but a saturation of the fuelling efficiency is observed at high injected mass as
needed for runaway electron suppression. Large locked modes can significantly decrease the fuelling efficiency and increase
the asymmetry of radiated power during MGI mitigation. Concerning power exhaust, the partially detached ITER divertor
scenario has been demonstrated at
P
sep
/R
=
10 MW m
−
1
in ASDEX Upgrade, with a peak time averaged target load around
5MWm
−
2
, well consistent with the component limits for ITER. Developing this towards DEMO, full detachment was achieved
at
P
sep
/R
=
7MWm
−
1
and stationary discharges with core radiation fraction of the order of DEMO requirements (70% instead
of the 30% needed for ITER) were demonstrated. Finally, it remains difficult to establish the standard ITER
Q
=
10 scenario at
low
q
95
=
3 in the all-tungsten (all-W) ASDEX Upgrade due to the observed poor confinement at low
β
N
. This is mainly due to
a degraded pedestal performance and hence investigations at shifting the operational point to higher
β
N
by lowering the current
have been started. At higher
q
95
, pedestal performance can be recovered by seeding N
2
as well as CD
4
, which is interpreted as
improved pedestal stability due to the decrease of bootstrap current with increasing
Z
eff
. Concerning advanced scenarios, the
upgrade of ECRH power has allowed experiments with central ctr-ECCD to modify the
q
-profile in improved H-mode scenarios,
showing an increase in confinement at still good MHD stability with flat elevated
q
-profiles at values between 1.5 and 2.European Commission (EUROfusion 633053
Overview of ASDEX Upgrade results
The ASDEX Upgrade (AUG) programme is directed towards physics input to critical
elements of the ITER design and the preparation of ITER operation, as well as addressing
physics issues for a future DEMO design. Since 2015, AUG is equipped with a new pair of
3-strap ICRF antennas, which were designed for a reduction of tungsten release during ICRF
operation. As predicted, a factor two reduction on the ICRF-induced W plasma content could
be achieved by the reduction of the sheath voltage at the antenna limiters via the compensation
of the image currents of the central and side straps in the antenna frame. There are two main
operational scenario lines in AUG. Experiments with low collisionality, which comprise
current drive, ELM mitigation/suppression and fast ion physics, are mainly done with freshly
boronized walls to reduce the tungsten influx at these high edge temperature conditions. Full
ELM suppression and non-inductive operation up to a plasma current of Ip = 0.8 MA could
be obtained at low plasma density. Plasma exhaust is studied under conditions of high neutral
divertor pressure and separatrix electron density, where a fresh boronization is not required.
Substantial progress could be achieved for the understanding of the confinement degradation
by strong D puffing and the improvement with nitrogen or carbon seeding. Inward/outward
shifts of the electron density profile relative to the temperature profile effect the edge stability
via the pressure profile changes and lead to improved/decreased pedestal performance.
Seeding and D gas puffing are found to effect the core fueling via changes in a region of high
density on the high field side (HFSHD).
The integration of all above mentioned operational scenarios will be feasible and
naturally obtained in a large device where the edge is more opaque for neutrals and higher
plasma temperatures provide a lower collisionality. The combination of exhaust control
with pellet fueling has been successfully demonstrated. High divertor enrichment values of
nitrogen EN 10 have been obtained during pellet injection, which is a prerequisite for the
simultaneous achievement of good core plasma purity and high divertor radiation levels.
Impurity accumulation observed in the all-metal AUG device caused by the strong neoclassical
inward transport of tungsten in the pedestal is expected to be relieved by the higher
neoclassical temperature screening in larger devices.European Commission (EUROfusion 633053
Cyttaria hariotii E.Fisch. as a promising source of pullulan and Mn(II)-pullulan complexes for Mn-deficiency remediation in winter cereals
Pullulan, a water-soluble polysaccharide consisting of maltotriose units used in the preparation of edible films and drug delivery, is generally produced from starch by Aureobasidium pullulans (de Bary & Löwenthal) G.Arnaud fungus. In this article, the characterisation of an alternative pullulan source - the stromata of Cyttaria hariotii E.Fisch. fungus - by elemental analysis, infrared spectroscopy and thermal analysis techniques is reported. With a view to a possible valorisation of this pullulan and its derivatives as bioactive formulations in agriculture, low-molecular-weight pullulan (<7 kDa) complexes with Mn(II), suitable for the remediation of Mn-deficiencies in winter cereal by foliar application, were synthesised and characterised by mass spectrometry
Optimal classification of Gaussian processes in homo- and heteroscedastic settings
A procedure to derive optimal discrimination rules is formulated for binary functional classification problems in which the instances available for induction are characterized by random trajectories sampled from different Gaussian processes, depending on the class label. Specifically, these optimal rules are derived as the asymptotic form of the quadratic discriminant for the discretely monitored trajectories in the limit that the set of monitoring points becomes dense in the interval on which the processes are defined. The main goal of this work is to provide a detailed analysis of such optimal rules in the dense monitoring limit, with a particular focus on elucidating the mechanisms by which near-perfect classification arises. In the general case, the quadratic discriminant includes terms that are singular in this limit. If such singularities do not cancel out, one obtains near-perfect classification, which means that the error approaches zero asymptotically, for infinite sample sizes. This singular limit is a consequence of the orthogonality of the probability measures associated with the stochastic processes from which the trajectories are sampled. As a further novel result of this analysis, we formulate rules to determine whether two Gaussian processes are equivalent or mutually singular (orthogonal)The research has been supported by the Spanish Ministry of Economy, Industry, and Competitiveness—State Research Agency, Projects MTM2016-78751-P and TIN2016-76406-P(AEI/FEDER, UE), and Comunidad Autónoma de Madrid, Project S2017/BMD-368
Short term visual outcomes of a new trifocal intraocular lens
Background: Today, patients often expect to achieve spectacle independance after cataract surgery. New trifocal intraocular lenses have been developed to try and fullfill this demand. The purpose of this study is to report the short-term visual outcomes of a new trifocal intraocular lens (AcrySof PanOptix™). Methods: Consecutive adult patients undergoing cataract surgery with bilateral implantation of the study intraocular lens in a private practice clinic were considered for inclusion. Exclusion criteria were the presence of other ocular pathologies or preoperative astigmatism >1.5 diopters (D). Patients with intraoperative complications were excluded from analysis. One month after surgery patients underwent: monocular defocus curve; monocular and binocular uncorrected visual acuity in photopic and mesopic conditions, for far (4 m), intermediate (60 cm) and near (33 cm) distances and binocular contrast sensitivity. Patients completed a visual satisfaction questionnaire between 9 and 12 months after surgery. Results: One hundred and sixteen eyes of fifty-eight patients receiving bilateral implantation of the study intraocular lens were analysed. Mean binocular uncorrected visual acuity in photopic conditions was 0.03 LogMAR for far, 0.12 for intermediate and 0.02 for near distances. All patients achieved a binocular uncorrected visual acuity better than 0.3 LogMAR (20/40 Snellen equivalent) for distance and near vision and 94.8% of patients for intermediate vision. Mesopic binocular uncorrected visual acuity values were similar to photopic values. The monocular defocus curves showed that the best visual acuity was reached at a vergence of 0.00D. Visual acuity dropped slightly at −1.00D and peaked again at −2.00D. Visual acuities better than 0.2 LogMAR were maintained between −2.50D and +0.50D. Contrast sensitivity was high and similar in photopic and mesopic conditions. As regards patient-evaluated outcomes, only 2 patients (3.4%) were fairly dissatisfied with their sight after surgery. Three patients (5.1%) reported the need for spectacle correction for certain activities. All other patients (94.8%) reported never using spectacle correction. Conclusions: The PanOptix trifocal IOL provides good short-term visual outcomes, with good intermediate performance and excellent patient-reported satisfaction. The similar values achieved in mesopic and photopic conditions in binocular uncorrected visual acuity and contrast sensitivity suggest low pupillary dependence for light distribution. Trial registration number: ISRCTN60143265 , retrospectively registered on the 24th of April 2017
Analysis of Quiet-Sun Internetwork Magnetic Fields Based on Linear Polarization Signals
We present results from the analysis of Fe I 630 nm measurements of the quiet
Sun taken with the spectropolarimeter of the Hinode satellite. Two data sets
with noise levels of 1.2{\times}10-3 and 3{\times}10-4 are employed. We
determine the distribution of field strengths and inclinations by inverting the
two observations with a Milne-Eddington model atmosphere. The inversions show a
predominance of weak, highly inclined fields. By means of several tests we
conclude that these properties cannot be attributed to photon noise effects. To
obtain the most accurate results, we focus on the 27.4% of the pixels in the
second data set that have linear polarization amplitudes larger than 4.5 times
the noise level. The vector magnetic field derived for these pixels is very
precise because both circular and linear polarization signals are used
simultaneously. The inferred field strength, inclination, and filling factor
distributions agree with previous results, supporting the idea that
internetwork fields are weak and very inclined, at least in about one quarter
of the area occupied by the internetwork. These properties differ from those of
network fields. The average magnetic flux density and the mean field strength
derived from the 27.4% of the field of view with clear linear polarization
signals are 16.3 Mx cm-2 and 220 G, respectively. The ratio between the average
horizontal and vertical components of the field is approximately 3.1. The
internetwork fields do not follow an isotropic distribution of orientations.Comment: To appear in APJ, Vol 749, 201
Participación en la interacción profesor-alumnos al resolver un problema con apartados de distintos dominios cognitivos en primaria
La interacción en las aulas es de interés en Educación Matemática, por ejemplo, referido a la participación de los alumnos cuando resuelven problemas conjuntamente con el profesor en el aula de Primaria. Rosales et al. (2008) muestran que es escasa cuando resuelven problemas rutinarios, aunque aumenta en los no rutinarios (Sánchez et al., 2014). Analizamos la participación en la interacción profesor-alumnos cuando resuelven juntos un problema con tres apartados (adaptado de TIMSS 2007, IEA, 2011) ubicados en los dominios de conocimiento, aplicación y razonamiento
High spatial resolution optical imaging of the multiple T Tauri system LkH{\alpha} 262/LkH{\alpha} 263
We report high spatial resolution i' band imaging of the multiple T Tauri
system LkH 262/LkH 263 obtained during the first commissioning
period of the Adaptive Optics Lucky Imager (AOLI) at the 4.2 m William Herschel
Telescope, using its Lucky Imaging mode. AOLI images have provided photometry
for each of the two components LkH 263 A and B (0.41 arcsec separation)
and marginal evidence for an unresolved binary or a disc in LkH 262.
The AOLI data combined with previously available and newly obtained optical and
infrared imaging show that the three components of LkH 263 are
co-moving, that there is orbital motion in the AB pair, and, remarkably, that
LkH 262-263 is a common proper motion system with less than 1 mas/yr
relative motion. We argue that this is a likely five-component gravitationally
bounded system. According to BT-settl models the mass of each of the five
components is close to 0.4 M and the age is in the range 1-2 Myr. The
presence of discs in some of the components offers an interesting opportunity
to investigate the formation and evolution of discs in the early stages of
multiple very low-mass systems. In particular, we provide tentative evidence
that the disc in 263C could be coplanar with the orbit of 263AB.Comment: 11 pages, 7 figures, Accepted 2016 May
Overview of progress in European medium sized tokamaks towards an integrated plasma-edge/wall solution
Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads
to tolerable heat and particle loads on the wall is a major challenge. The new European
medium size tokamak task force (EU-MST) coordinates research on ASDEX Upgrade
(AUG), MAST and TCV. This multi-machine approach within EU-MST, covering a wide
parameter range, is instrumental to progress in the field, as ITER and DEMO core/pedestal
and SOL parameters are not achievable simultaneously in present day devices. A two prong
approach is adopted. On the one hand, scenarios with tolerable transient heat and particle
loads, including active edge localised mode (ELM) control are developed. On the other hand,
divertor solutions including advanced magnetic configurations are studied. Considerable
progress has been made on both approaches, in particular in the fields of: ELM control with
resonant magnetic perturbations (RMP), small ELM regimes, detachment onset and control,
as well as filamentary scrape-off-layer transport. For example full ELM suppression has now
been achieved on AUG at low collisionality with n = 2 RMP maintaining good confinement
HH(98,y2) 0.95. Advances have been made with respect to detachment onset and control.
Studies in advanced divertor configurations (Snowflake, Super-X and X-point target divertor)
shed new light on SOL physics. Cross field filamentary transport has been characterised in a
wide parameter regime on AUG, MAST and TCV progressing the theoretical and experimental
understanding crucial for predicting first wall loads in ITER and DEMO. Conditions in the
SOL also play a crucial role for ELM stability and access to small ELM regimes.European Commission (EUROfusion 633053
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