691 research outputs found
Early evolution of electron cyclotron driven current during suppression of tearing modes in a circular tokamak
When electron cyclotron (EC) driven current is first applied to the inside of
a magnetic island, the current spreads throughout the island and after a short
period achieves a steady level. Using a two equation fluid model for the EC
current that allows us to examine this early evolution in detail, we analyze
high-resolution simulations of a 2/1 classical tearing mode in a low-beta large
aspect-ratio circular tokamak. These simulations use a nonlinear 3D reduced-MHD
fluid model and the JOREK code. During the initial period where the EC driven
current grows and spreads throughout the magnetic island, it is not a function
of the magnetic flux. However, once it has reached a steady-state, it should be
a flux function. We demonstrate numerically that if sufficiently resolved
toroidally, the steady-state EC driven current becomes approximately a flux
function. We discuss the physics of this early period of EC evolution and its
impact on the size of the magnetic island.Comment: 12 pages, 7 figure
How perceived scarcity predicted cooperation during early pandemic lockdown.
Both material resources (jobs, healthcare), and socio-psychological resources (social contact) decreased during the COVID-19 pandemic. We investigated whether individual differences in perceived material and socio-psychological scarcity experienced during the pandemic predicted preference for cooperation, measured using two Public Good Games (PGGs), where participants contributed money or time (i.e., hours indoors contributed to shorten the lockdown). Material scarcity had no relationship with cooperation. Increased perceived scarcity of socio-psychological wellbeing (e.g., connecting with family) predicted increased preference for cooperation, suggesting that missing social contact fosters prosociality, whilst perceived scarcity of freedom (e.g., limited movement) predicted decreased willingness to spend time indoors to shorten the lockdown. The importance of considering individual differences in scarcity perception to best promote norm compliance is discussed
Neurocognitive mechanisms of reactions to second- and third-party justice violations.
The aim of the current study was threefold: (i) understand people's willingness to engage in either punishment of the perpetrator or compensation of the victim in order to counteract injustice; (ii) look into the differences between victims of and witnesses to injustice; (iii) investigate the different role played by social preference and affective experience in determining these choices. The sample tested here showed an equal preference for punishment and compensation; neuroimaging findings suggested that compensation, as opposed to punishment, was related to Theory of Mind. Partially supporting previous literature, choosing how to react to an injustice as victims, rather than witnesses, triggered a stronger affective response (striatal and prefrontal activation). Moreover, results supported the idea that deciding whether or not to react to an injustice and then how severely to react are two distinct decisional stages underpinned by different neurocognitive mechanisms, i.e., sensitivity to unfairness (anterior insula) and negative affectivity (amygdala). These findings provide a fine-grained description of the psychological mechanisms underlying important aspects of social norm compliance
Farming, Gender and Aspirations across Young People's Life Course
Drawing on life history interviews conducted in Indian and Indonesian study sites, we tease out the social production of aspirations in the process of becoming a farmer. We show the power of a doxic logic in which schooling is regarded as the pathway out of farming, towards a future of non-manual, salaried employment. Among rural youth this doxic logic produces broadly defined aspiration such as ‘completing education’, and ‘getting a job’. In the absence of clear pathways to realise such aspirations, young people seek to keep options open. Yet, the scope for doing so changes in relation to key life events such as ending school, migration and marriage and does so in distinctly gendered ways. We conclude proposing that young people’s delayed entrance into farming, among other things, must be understood as an attempt to keep open those futures that are considered closed by an early entry into full-time farming
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
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