267,982 research outputs found
2D continuous spectrum of shear Alfven waves in the presence of a magnetic island
The radial structure of the continuous spectrum of shear Alfven modes is
calculated in the presence of a magnetic island in tokamak plasmas. Modes with
the same helicity of the magnetic island are considered in a slab model
approximation. In this framework, with an appropriate rotation of the
coordinates the problem reduces to 2 dimensions. Geometrical effects due to the
shape of the flux surface's cross section are retained to all orders. On the
other hand, we keep only curvature effects responsible of the beta induced gap
in the low-frequency part of the continuous spectrum. New continuum
accumulation points are found at the O-point of the magnetic island. The
beta-induced Alfven Eigenmodes (BAE) continuum accumulation point is found to
be positioned at the separatrix flux surface. The most remarkable result is the
nonlinear modification of the BAE continuum accumulation point frequency
Control of laser wake field acceleration by plasma density profile
We show that both the maximum energy gain and the accelerated beam quality
can be efficiently controlled by the plasma density profile. Choosing a proper
density gradient one can uplift the dephasing limitation. When a periodic wake
field is exploited, the phase synchronism between the bunch of relativistic
particles and the plasma wave can be maintained over extended distances due to
the plasma density gradient. Putting electrons into the th wake period
behind the driving laser pulse, the maximum energy gain is increased by the
factor over that in the case of uniform plasma. The acceleration is
limited then by laser depletion rather than by dephasing. Further, we show that
the natural energy spread of the particle bunch acquired at the acceleration
stage can be effectively removed by a matched deceleration stage, where a
larger plasma density is used
Controlling electron-electron correlation in frustrated double ionization of molecules with orthogonally polarized two-color laser fields
We demonstrate the control of electron-electron correlation in frustrated
double ionization (FDI) of the two-electron triatomic molecule D when
driven by two orthogonally polarized two-color laser fields. We employ a
three-dimensional semi-classical model that fully accounts for the electron and
nuclear motion in strong fields. We analyze the FDI probability and the
distribution of the momentum of the escaping electron along the polarization
direction of the longer wavelength and more intense laser field. These
observables when considered in conjunction bear clear signatures of the
prevalence or absence of electron-electron correlation in FDI, depending on the
time-delay between the two laser pulses. We find that D is a better
candidate compared to H for demonstrating also experimentally that
electron-electron correlation indeed underlies FDI.Comment: 5 pages, 4 figure
Temperature-resonant cyclotron spectra in confined geometries
We consider a two-dimensional gas of colliding charged particles confined to
finite size containers of various geometries and subjected to a uniform
orthogonal magnetic field. The gas spectral densities are characterized by a
broad peak at the cyclotron frequency. Unlike for infinitely extended gases,
where the amplitude of the cyclotron peak grows linearly with temperature, here
confinement causes such a peak to go through a maximum for an optimal
temperature. In view of the fluctuation-dissipation theorem, the reported
resonance effect has a direct counterpart in the electric susceptibility of the
confined magnetized gas
Effects of energetic particles on zonal flow generation by toroidal Alfven eigenmode
Generation of zonal ow (ZF) by energetic particle (EP) driven toroidal Alfven
eigenmode (TAE) is investigated using nonlinear gyrokinetic theory. It is found
that, nonlinear resonant EP contri- bution dominates over the usual Reynolds
and Maxwell stresses due to thermal plasma nonlinear response. ZF can be forced
driven in the linear growth stage of TAE, with the growth rate being twice the
TAE growth rate. The ZF generation mechanism is shown to be related to
polarization induced by resonant EP nonlinearity. The generated ZF has both the
usual meso-scale and micro- scale radial structures. Possible consequences of
this forced driven ZF on the nonlinear dynamics of TAE are also discussed.Comment: To be submitted to Physics of Plasma
Perturbational approach to the quantum capacity of additive Gaussian quantum channel
For a quantum channel with additive Gaussian quantum noise, at the large
input energy side, we prove that the one shot capacity is achieved by the
thermal noise state for all Gaussian state inputs, it is also true for
non-Gaussian input in the sense of first order perturbation. For a general case
of copies input, we show that up to first order perturbation, any
non-Gaussian perturbation to the product thermal state input has a less quantum
information transmission rate when the input energy tend to infinitive.Comment: 5 page
High-performance -type organic field-effect transistors with ionic liquid gates
High-performance -type organic field-effect transistors were developed
with ionic-liquid gates and N,N-bis(n-alkyl)-(1,7 and
1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide)s single-crystals. Transport
measurements show that these devices reproducibly operate in ambient atmosphere
with negligible gate threshold voltage and mobility values as high as 5.0
cm/Vs. These mobility values are essentially identical to those measured in
the same devices without the ionic liquid, using vacuum or air as the gate
dielectric. Our results indicate that the ionic-liquid and -type organic
semiconductor interfaces are suitable to realize high-quality -type organic
transistors operating at small gate voltage, without sacrificing electron
mobility
Lattice Boltzmann Thermohydrodynamics
We introduce a lattice Boltzmann computational scheme capable of modeling
thermohydrodynamic flows of monatomic gases. The parallel nature of this
approach provides a numerically efficient alternative to traditional methods of
computational fluid dynamics. The scheme uses a small number of discrete
velocity states and a linear, single-time-relaxation collision operator.
Numerical simulations in two dimensions agree well with exact solutions for
adiabatic sound propagation and Couette flow with heat transfer.Comment: 11 pages, Physical Review E: Rapid Communications, in pres
Supersolid phases in the extended boson hubbard model
We present a comprehensive numerical study on the ground state phase diagram
of the two-dimensional hardcore boson extended Hubbard model with nearest
() and next nearest neighbor () repulsions. In addition to the
quantum solid and superfluid phases, we report the existence of striped
supersolid and three-quarter (quarter) filled supersolid at commensurate
density (0.25) due to the interplay of and
interactions. The nature of three-quarter filled supersolid and the associated
quantum solid will be discussed. Quantum phase transition between the two
supersolids of different symmetries is observed and is clearly of first order.Comment: 4 pages, 6 figure
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