964 research outputs found
An exploratory study of cultural differences and perceptions of relational risk
This working paper is part of a research project examining the role of culture and culture differences in foreign partnerships. We build on prior research on culture distance to explore the influence of perceptions of cultural differences on perceived relational risk. Perceived
relational risk is defined here as the degree of satisfaction of being involved in business activities with nationals of a given country. Contrary to expectations, preliminary analysis suggests that cultural differences are sometimes perceived as a desirable characteristic and may be associated with lower relational risk. We speculate that culture distance is an
asymmetric construct in which the perception of a cultural difference may be interpreted as positive or negative depending on the perspective from which the reading is made and the nature of the task in which the perception is formed. Plans for future research are discussed
Observation of lobes near the X-point in resonant magnetic perturbation experiments on MAST
The application of non-axisymmetric resonant magnetic perturbations (RMPs)
with a toroidal mode number n=6 in the MAST tokamak produces a significant
reduction in plasma energy loss associated with type-I Edge Localized Modes
(ELMs), the first such observation with n>3. During the ELM mitigated stage
clear lobe structures are observed in visible-light imaging of the X-point
region. These lobes or manifold structures, that were predicted previously,
have been observed for the first time in a range of discharges and their
appearance is correlated with the effect of RMPs on the plasma i.e. they only
appear above a threshold when a density pump out is observed or when the ELM
frequency is increased. They appear to be correlated with the RMPs penetrating
the plasma and may be important in explaining why the ELM frequency increases.
The number and location of the structures observed can be well described using
vacuum modelling. Differences in radial extent and poloidal width from vacuum
modelling are likely to be due to a combination of transport effects and plasma
screening.Comment: 15 pages, 5 figure
Non-linear Simulations of MHD Instabilities in Tokamaks Including Eddy Current Effects and Perspectives for the Extension to Halo Currents
The dynamics of large scale plasma instabilities can strongly be influenced
by the mutual interaction with currents flowing in conducting vessel
structures. Especially eddy currents caused by time-varying magnetic
perturbations and halo currents flowing directly from the plasma into the walls
are important. The relevance of a resistive wall model is directly evident for
Resistive Wall Modes (RWMs) or Vertical Displacement Events (VDEs). However,
also the linear and non-linear properties of most other large-scale
instabilities may be influenced significantly by the interaction with currents
in conducting structures near the plasma. The understanding of halo currents
arising during disruptions and VDEs, which are a serious concern for ITER as
they may lead to strong asymmetric forces on vessel structures, could also
benefit strongly from these non-linear modeling capabilities. Modeling the
plasma dynamics and its interaction with wall currents requires solving the
magneto-hydrodynamic (MHD) equations in realistic toroidal X-point geometry
consistently coupled with a model for the vacuum region and the resistive
conducting structures. With this in mind, the non-linear finite element MHD
code JOREK has been coupled with the resistive wall code STARWALL, which allows
to include the effects of eddy currents in 3D conducting structures in
non-linear MHD simulations. This article summarizes the capabilities of the
coupled JOREK-STARWALL system and presents benchmark results as well as first
applications to non-linear simulations of RWMs, VDEs, disruptions triggered by
massive gas injection, and Quiescent H-Mode. As an outlook, the perspectives
for extending the model to halo currents are described.Comment: Proceeding paper for Theory of Fusion Plasmas (Joint Varenna-Lausanne
International Workshop), Varenna, Italy (September 1-5, 2014); accepted for
publication in: to Journal of Physics: Conference Serie
Electron acceleration in a JET disruption simulation
Runaways are suprathermal electrons having sufficiently high energy to be
continuously accelerated up to tens of MeV by a driving electric field [1].
Highly energetic runaway electron (RE) beams capable of damaging the tokamak
first wall can be observed after a plasma disruption [2]. Therefore, it is of
primary importance to fully understand their generation mechanisms in order to
design mitigation systems able to guarantee safe tokamak operations. In a
previous work, [3], a test particle tracker was introduced in the JOREK 3D
non-linear MHD code and used for studying the electron confinement during a
simulated JET-like disruption. It was found in [3] that relativistic electrons
are not completely deconfined by the stochastic magnetic field taking place
during the disruption thermal quench (TQ). This is due to the reformation of
closed magnetic surfaces at the beginning of the current quench (CQ). This
result was obtained neglecting the inductive electric field in order to avoid
the unrealistic particle acceleration which otherwise would have happened due
to the absence of collision effects. The present paper extends [3] analysing
test electron dynamics in the same simulated JET-like disruption using the
complete electric field. For doing so, a simplified collision model is
introduced in the particle tracker guiding center equations. We show that
electrons at thermal energies can become RE during or promptly after the TQ due
to a combination of three phenomena: a first REs acceleration during the TQ due
to the presence of a complex MHD-induced electric field, particle reconfinement
caused by the fast reformation of closed magnetic surfaces after the TQ and a
secondary acceleration induced by the CQ electric field
NIR-emission from Yb(III)- and Nd(III)-based complexes in the solid state sensitized by a ligand system absorbing in a broad UV and visible spectral window
In this contribution, we present the synthesis, characterization and spectroscopic investigation of the heteroleptic (R,R)-YbL1(tta) and (R,R)-NdL1(tta) complexes (with tta = 2-thenoyltrifluoroacetonate and L1 = N,N'-bis(2-(8-hydroxyquinolinate)methylidene)-1,2-(R,R or S,S)-cyclohexanediamine) in the solid state. The f-f metal-centered NIR luminescence emission of Nd(III) and Yb(III) is efficiently sensitized by both chromophoric ligands in a very broad range of wavelengths [from 250 to 600 nm, in the case of Nd(III) and from 250 to 650 nm, for Yb(III)]. A possible energy transfer mechanism is proposed: for (R,R)-NdL1(tta) complex a classical Ligand-to-Metal Energy Transfer (LMET) mechanism (antenna effect) is suggested, whilst in the case of the (R,R)-YbL1(tta) complex, the presence of a ligand-to-metal charge transfer (LMCT) state determines the sensitization of Yb(III) luminescence. We propose that this level is populated by the singlet and triplet excited states belonging to pi -> pi* and n -> pi* transitions of both ligands and it can transfer the excitation energy to F-2(5/2)
Coupling JOREK and STARWALL for Non-linear Resistive-wall Simulations
The implementation of a resistive-wall extension to the non-linear MHD-code
JOREK via a coupling to the vacuum-field code STARWALL is presented along with
first applications and benchmark results. Also, non-linear saturation in the
presence of a resistive wall is demonstrated. After completion of the ongoing
verification process, this code extension will allow to perform non-linear
simulations of MHD instabilities in the presence of three-dimensional resistive
walls with holes for limited and X-point plasmas.Comment: Contribution for "Theory Of Fusion Plasmas, Joint Varenna - Lausanne
International Workshop, Villa Monastero, Varenna, Italy (27.-31.8.2012)",
accepted for publication in Journal of Physics Conference Serie
Three-dimensional non-linear magnetohydrodynamic modeling of massive gas injection triggered disruptions in JET
JOREK 3D non-linear MHD simulations of a D2 Massive Gas Injection (MGI) triggered disruption
in JET are presented and compared in detail to experimental data. The MGI creates an overdensity
that rapidly expands in the direction parallel to the magnetic field. It also causes the growth of
magnetic islands (m=n ¼ 2=1 and 3/2 mainly) and seeds the 1/1 internal kink mode. O-points of
all island chains (including 1/1) are located in front of the MGI, consistently with experimental
observations. A burst of MHD activity and a peak in plasma current take place at the same time
as in the experiment. However, the magnitude of these two effects is much smaller than in the
experiment. The simulated radiation is also much below the experimental level. As a consequence, the thermal quench is not fully reproduced. Directions for progress are identified. Radiation from impurities is a good candidate.EURATOM 63305
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