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Can Merchant Interconnectors Deliver Lower and More Stable Prices? The Case of NorNed
Fast growing double tearing modes in a tokamak plasma
Configurations with nearby multiple resonant surfaces have broad spectra of
linearly unstable coupled tearing modes with dominant high poloidal mode
numbers m. This was recently shown for the case of multiple q = 1 resonances
[Bierwage et al., Phys. Rev. Lett. 94 (6), 65001 (2005)]. In the present work,
similar behavior is found for double tearing modes (DTM) on resonant surfaces
with q >= 1. A detailed analysis of linear instability characteristics of DTMs
with various mode numbers m is performed using numerical simulations. The mode
structures and dispersion relations for linearly unstable modes are calculated.
Comparisons between low- and higher-m modes are carried out, and the roles of
the inter-resonance distance and of the magnetic Reynolds number S_Hp are
investigated. High-m modes are found to be destabilized when the distance
between the resonant surfaces is small. They dominate over low-m modes in a
wide range of S_Hp, including regimes relevant for tokamak operation. These
results may be readily applied to configurations with more than two resonant
surfaces.Comment: 11 pages, 15 figure
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Properties of Electricity Prices and the Drivers of Interconnector Revenue
This paper examines the drivers behind revenues of merchant electricity interconnectors and the effect of arbitrage trading over interconnectors on the level and volatility of electricity prices in the connected markets. It sets out a simulation methodology that allows the stochastic and deterministic properties of prices, as well as most model parameters, to be varied freely. The effect of electricity flows over interconnectors on prices and thus on interconnector revenues is modelled explicitly by a mathematical algorithm. It is found that arbitrage can reduce the volatility and to some extent the mean of electricity prices in both markets when two markets with a similar distribution of prices are connected. It is also found that it is possible for interconnectors to generate considerable revenues without any consistent price differences between the connected markets. This shows that interconnectors between seemingly very similar electricity markets can be an attractive proposition for a profit-seeking investor
Dynamics of resistive double tearing modes with broad linear spectra
The nonlinear evolution of resistive double tearing modes (DTMs) with safety
factor values q=1 and q=3 is studied in a reduced cylindrical model of a
tokamak plasma. We focus on cases where the resonant surfaces are a small
distance apart. Recent numerical studies have shown that in such configurations
high-m modes are strongly unstable. In this paper, it is first demonstrated
that linear DTM theory predicts the dominance of high-m DTMs. A semi-empirical
formula for estimating the poloidal mode number of the fastest growing mode,
m_peak, is obtained from the existing linear theory. Second, using nonlinear
simulations, it is shown that the presence of fast growing high-m modes leads
to a rapid turbulent collapse in an annular region, whereby small magnetic
island structures form. Furthermore, consideration is given to the evolution of
low-m modes, in particular the global m=1 internal kink, which can undergo
nonlinear driving through coupling to fast growing linear high-m DTMs. Factors
influencing the details of the dynamics are discussed. These results may be
relevant for the understanding of the magnetohydrodynamic (MHD) activity near
the minimum of q and may thus be of interest to studies concerned with
stability and confinement in advanced tokamaks.Comment: 11 pages, 10 figure
Self-consistent nonlinear kinetic simulations of the anomalous Doppler instability of suprathermal electrons in plasmas
Suprathermal tails in the distributions of electron velocities parallel to the magnetic field are found in many areas of plasma physics, from magnetic confinement fusion to solar system plasmas. Parallel electron kinetic energy can be transferred into plasma waves and perpendicular gyration energy of particles through the anomalous Doppler instability (ADI), provided that energetic electrons with parallel velocities v ≥ (ω + Ωce )/k are present; here Ωce denotes electron cyclotron frequency, ω the wave angular frequency and k the component of wavenumber parallel to the magnetic field. This phenomenon is widely observed in tokamak plasmas. Here we present the first fully self-consistent relativistic particle-in-cell simulations of the ADI, spanning the linear and nonlinear regimes of the ADI. We test the robustness of the analytical theory in the linear regime and follow the ADI through to the steady state. By directly evaluating the parallel and perpendicular dynamical contributions to j · E in the simulations, we follow the energy transfer between
the excited waves and the bulk and tail electron populations for the first time. We find that the ratio Ωce /(ωpe + Ωce ) of energy transfer between parallel and perpendicular, obtained from linear analysis, does not apply when damping is fully included, when we find it to be ωpe /(ωpe + Ωce ); here ωpe denotes the electron plasma frequency. We also find that the ADI can arise beyond the previously expected range of plasma parameters, in particular when Ωce > ωpe . The simulations also exhibit a spectral feature which may
correspond to observations of suprathermal narrowband emission at ωpe detected from low density tokamak plasmas
Quasi-linear analysis of the extraordinary electron wave destabilized by runaway electrons
Runaway electrons with strongly anisotropic distributions present in
post-disruption tokamak plasmas can destabilize the extraordinary electron
(EXEL) wave. The present work investigates the dynamics of the quasi-linear
evolution of the EXEL instability for a range of different plasma parameters
using a model runaway distribution function valid for highly relativistic
runaway electron beams produced primarily by the avalanche process. Simulations
show a rapid pitch-angle scattering of the runaway electrons in the high energy
tail on the time scale. Due to the wave-particle
interaction, a modification to the synchrotron radiation spectrum emitted by
the runaway electron population is foreseen, exposing a possible experimental
detection method for such an interaction
Seguendo Grothendieck
Abstract
Neoclassical transport of tungsten ion bundles in total-f neoclassical gyrokinetic simulations of a whole-volume JET-like plasma
Neoclassical gyrokinetic simulations including tungsten impurities are
carried out using multiple gyrokinetic bundles to model the many charge states
of tungsten ions present in the whole-volume of a model H-mode plasma in JET
geometry. A gyrokinetic bundle regroups tungsten ions of similar charge
together in order to decrease the computational cost. The initial radial shape
of the bundles and their individual charges are deduced from a coronal
approximation and from quasi-neutrality of the plasma. Low-Z tungsten ions move
radially inward from SOL into the core region, whereas high-Z tungsten ions
move radially outwardly from the core and inwardly from the separatrix. These
fluxes lead to an accumulation of tungsten in the pedestal top of our test
case. This organization of the fluxes cannot be captured by a single
tungsten-ion simulation. Large up/down poloidal asymmetries of tungsten form in
the pedestal and strongly influence the direction of these neoclassical fluxes.
Future implementation of atomic interactions between bundles is discussed.Comment: 11 pages, 11 figure
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