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arXiv2013

A mixed SOC-turbulence model for nonlocal transport and space-fractional Fokker-Planck equation

The phenomena of nonlocal transport in magnetically confined plasma are theoretically analyzed. A hybrid model is proposed, which brings together the notion of inverse energy cascade, typical of drift-wave- and two-dimensional fluid turbulence, and the ideas of avalanching behavior, associable with self-organized critical (SOC) behavior. Using statistical arguments, it is shown that an amplification mechanism is needed to introduce nonlocality into dynamics. We obtain a consistent derivation of nonlocal Fokker-Planck equation with space-fractional derivatives from a stochastic Markovian process with the transition probabilities defined in reciprocal space.

physics.plasm-ph↗

arXiv2013

Plasma effect in the longitudinal space charge induced microbunching instability for low energy electron beams

The microbunching instability usually exists in the LINAC of a free electron laser (FEL) facility. In many cases, the longitudinal space charge (LSC) is a dominant factor that generates the instability. For the highly bright electron beams, the plasma effect is found to be non-trivial in the development of the instability. In this paper, starting from the Vlasov and Poisson equations in the multiple-dimensional phase space, we perform the straightforward analysis of the microbunching instability based on the explicit formula of the longitudinal electric field introduced by the density perturbation in the longitudinal direction, in such a way to be highly comparable to the well-developed method for higher energy beams. This method generally applies in both the cases with and without acceleration and independent of lattice components. The results show that for a electron beam with small transverse emittance at low energies, which is always the case in the injector of a free electron laser device, the plasma effect results in the oscillation of the longitudinal electric field in the modified plasma frequency that depends on the transverse size of the beam, and the Landau damping effect in the longitudinal electric field due to the uncorrelated longitudinal velocity spread during the beam transportation. These two effects both play important roles in the development of the instability. As the result, the energy modulation driven by the LSC impedance differs from the regular value significantly and the discrepancy leads to the noticeable change of the final gain of the instability.

physics.acc-ph↗

arXiv2013

Stochastic Theory of Dust-Grain Charging in Low-Pressure Plasmas

Charging of dust grains in low-pressure plasmas is reviewed critically. A theory based on the Fokker-Planck equation and orbital motion limited approximation is proposed. The theory predicts that dust grains can acquire a positive charge in low-pressure electropositive plasmas having a sufficiently high plasma potential, in agreement with experimental observations. It is also shown that variations in the plasma potential (electron temperature) can lead to spatial regions in which grains have opposite charges.

physics.plasm-ph↗

arXiv2013

Fabrication of High Aspect Ratio Micro-Penning-Malmberg Gold Plated Silicon Trap Arrays

Acquiring a portable high density charged particles trap might consist of an array of micro-Penning-Malmberg traps (microtraps) with substantially lower end barriers potential than conventional Penning-Malmberg traps [1]. We report on the progress of the fabrication of these microtraps designed for antimatter storage such as positrons. The fabrication of large length to radius aspect ratio (1000:1) microtrap arrays involved advanced techniques including photolithography, deep reactive ion etching (DRIE) of silicon wafers to achieve through-vias, gold sputtering of the wafers on the surfaces and inside the vias, and thermal compression bonding of the wafers. This paper describes the encountered issues during fabrication and addresses geometry errors and asymmetries. In order to minimize the patch effects on the lifetime of the trapped positrons, the bonded stacks were gold electroplated to achieve a uniform gold surface. We show by simulation and analytical calculation that how positrons confinement time depends on trap imperfections.

physics.ins-det↗

arXiv2013

Study of Conduction Cooling Effects in Long Aspect Ratio Penning-Malmberg Micro-Traps

A first order perturbation with respect to velocity has been employed to find the frictional damping force imposed on a single moving charge due to a perturbative electric field, inside a long circular cylindrical trap. We find that the electric field provides a cooling effect, has a tensorial relationship with the velocity of the charge. A mathematical expression for the tensor field has been derived and numerically estimated. The corresponding drag forces for a charge moving close to the wall in a cylindrical geometry asymptotically approaches the results for a flat surface geometry calculated in the literature. Many particle conduction cooling power dissipation is formulated using the single particle analysis. Also the cooling rate for a weakly interacting ensemble is estimated. It is suggested that a pre-trap section with relatively high electrical resistivity can be employed to cool down low density ensembles of electrons/positrons before being injected into the trap. For a micro-trap with tens of thousands of micro-tubes, hundreds of thousands of particles can be cooled down in each cooling cycle. For example, tens of particles per micro-tube in a $5 cm$ long pre-trap section with the resistivity of $0.46 Ωm$ and the micro-tubes of radius $50 μm$ can be cooled down with the time constant of $106μs$.

physics.plasm-ph↗

arXiv2013

The Quadratic Coefficient of the Electron Cloud Mapping

The Electron Cloud is an undesirable physical phenomenon which might produce single and multi-bunch instability, tune shift, increase of pressure ultimately limiting the performance of particle accelerators. We report our results on the analytical study of the electron dynamics.

physics.acc-ph↗

arXiv2013

Relativistic Frequency Synthesis of Light Fields

Waveform shaping and frequency synthesis based on waveform modulation is ubiquitous in electronics, telecommunication technology, and optics. For optical waveforms, the carrier frequency is on the order of several hundred THz, while the modulation frequencies used in conventional devices like electro- or acousto-optical modulators are orders of magnitude lower. As a consequence, any new frequencies are typically very close to the fundamental. The synthesis of new frequencies in the extreme ultraviolet (XUV), e.g. by using relativistic oscillating mirrors, requires modulation frequencies in the optical regime or even in the extreme ultraviolet. The latter has not been proven possible to date. Here we demonstrate that individual strong harmonics can indeed be generated by reflecting light off a plasma surface that oscillates at XUV frequencies. The strong harmonics are explained by nonlinear frequency mixing of near-infrared light and a laser-driven plasma oscillation in the extreme ultra-violet mediated by a relativistic non-linearity.

physics.plasm-ph↗

arXiv2013

QM theory of the thermal electron gyroradius

The average (thermal) gyroradius of charged particles is re-examined from a quantum-mechanical point of view. The straight quantum-mechanical calculation clearly reproduces its conventionally used random-mean-square (rms) expectation value. The quasi-classical approach reproduces its mean expectation value as well thus confirming the purely classical calculation. It shows that the fluctuations in the gyroradius amount to 21.5% of its rms value. This fluctuation is, however, within the usual $\sqrt{2}$-"freedom" range of choice in the definition of the rms gyroradius respectively the mean thermal speed on which the rms value is based, its correct (nonrelativistic) value $v_t^2= 2T_\perp/m_e$ and its simplified version $v_t^2=T_\perp/m_e$.

physics.plasm-ph↗

arXiv2013

Micron-Scale Mapping of Megagauss Magnetic Fields in Petawatt Laser-Solid Interactions

We report spatially and temporally resolved measurements of magnetic fields generated by petawatt laser-solid interactions with high spatial resolution, using optical polarimetry. The polarimetric measurements map the megagauss magnetic field profiles generated by the fast electron currents at the target rear. The magnetic fields at the rear of a 50 $μ$m thick aluminum target exhibit distinct and unambiguous signatures of electron beam filamentation. These results are corroborated by hybrid simulations.

physics.plasm-ph↗

arXiv2013

Neutrino oscillations in a turbulent plasma

A new model for the joint neutrino flavor and plasma oscillations is introduced, in terms of the dynamics of the neutrino flavor polarization vector in a plasma background. Fundamental solutions are found for both time-invariant and time-dependent media, considering slow and fast variations of the electron plasma density. The model is shown to be described by a generalized Hamiltonian formalism. In the case of a broad spectrum of electron plasma waves, a statistical approach indicate the shift of both equilibrium value and frequency oscillation of flavor coherence, due to the existence of a turbulent plasma background.

physics.plasm-ph↗

arXiv2013

Neutronics Analysis of the ITER In-Vessel Viewing System

The In-Vessel Viewing System (IVVS) in ITER consists of six identical units which are deployed between pulses or during shutdown, to perform visual examination and metrology of plasma facing components. The system is housed in dedicated ports at B1 level, with deployment at the level between the divertor cassettes and the lowermost outboard blanket modules. Boron carbide shielding blocks are envisaged to protect the sensitive components of the IVVS from damage during operations, and personnel from radiation fields. In order to progress the design of the IVVS beyond the pre-conceptual stage, analyses were conducted using MCNP to determine the acceptability of a series of different shielding configurations.

physics.ins-det↗

arXiv2013

Influence of quantum energy equation on electronic plasma oscillations

Five-moment approximation in hydrodynamics includes not only continuity equation and momentum balance equation, but also energy equation. Set of hydrodynamic equations is presented for system of non-relativistic quantum particles with Coulomb interaction. This set of equations is linearized, and dispersion relation for Langmuir waves in quasi-neutral system of electrons and immobile ions is obtained.

physics.plasm-ph↗

arXiv2013

Numerical modelling of Ar glow discharge at intermediate and high pressures

A detailed collisional-radiative model for Ar at intermediate and high pressures is developed. The model is coupled with the electron Boltzmann equation and includes several highly excited Ar states and charged particles. The densities of all neutral and charged species considered are calculated self-consistently. Detailed information concerning the electronic data used is presented. The model will be further used for analysing the contraction phenomena in noble gas discharges and eventually for theoretical description of the kinetic properties of high pressure Ar excimer laser.

physics.plasm-ph↗

arXiv2013

Particle in cell calculation of plasma force on a small grain in a non-uniform collisional sheath

The plasma force on grains of specified charge and height in a collisional DC plasma sheath are calculated using the multidimensional particle in cell code COPTIC. The background ion velocity distribution functions for the unperturbed sheath vary substantially with collisionality. The grain force is found to agree quite well with a combination of background electric field force plus ion drag force. However, the drag force must take account of the non-Maxwellian (and spatially varying) ion distribution function, and the collisional drag enhancement. It is shown how to translate the dimensionless results into practical equilibrium including other forces such as gravity.

physics.plasm-ph↗

arXiv2013

Note on the nature of the transition between a system in an equilibrium state and a system in a non-equilibrium state (and vice-versa)

The transition from a non-equilibrium state to an equilibrium state is characterized not only by the disappearance of the entropy production, but mainly by the disappearance of the organized currents, due to the gradients present in a non-equilibrium system. Their disappearance is necessary to obtain maximum entropy in the equilibrium state.

cond-mat.stat-mech↗

arXiv2013

Condensed phase effects on the electronic momentum distribution in the warm dense matter regime

We report ab initio calculations of the valence electron momentum distribution function n(p) and dynamic structure factor for warm dense Be at Mbar pressures. We observe an unexpected, strong reshaping of the Compton profile upon increasing density, even well before any significant core-wavefunction overlap or electride behavior occurs. We propose that this nonperturbative effect, which is due to a growing influence on n(p) of the orthogonalization of valence and core electron wave- functions with increasing density, is observable by inelastic x-ray scattering at x-ray free-electron lasers and large-scale laser-shock heating facilities, and may also be more generally important for thermodynamic properties of dense, partially-ionized plasmas.

physics.plasm-ph↗

arXiv2013

A high-order electromagnetic gyrokinetic model

A high-order extension is presented for the electromagnetic gyrokinetic formulation in which the parallel canonical momentum is taken as one of phase space coordinates. The high-order displacement vector associated with the guiding-center transformation should be considered in the long wavelength regime. This yields addtional terms in the gyrokinetic Hamiltonian which lead to modifications to the gyrokinetic Poisson and Ampère equations. In addition, the high-order piece of the guiding-center transformation for the parallel canonical momentum should be also kept in the electromagnetic model. The high-order piece contains the Baños drift effect and further modifies the gyrokinetic Ampère equation.

physics.plasm-ph↗

arXiv2013

Continuum Hamiltonian Hopf Bifurcation I

Hamiltonian bifurcations in the context of noncanonical Hamiltonian matter models are described. First, a large class of 1 + 1 Hamiltonian multi-fluid models is considered. These models have linear dynamics with discrete spectra, when linearized about homogeneous equilibria, and these spectra have counterparts to the steady state and Hamiltonian Hopf bifurcations when equilibrium parameters are varied. Examples of fluid sound waves and plasma and gravitational streaming are treated in detail. Next, using these 1 + 1 examples as a guide, a large class of 2 + 1 Hamiltonian systems is introduced, and Hamiltonian bifurcations with continuous spectra are examined. It is shown how to attach a signature to such continuous spectra, which facilitates the description of the continuous Hamiltonian Hopf bifurcation. This chapter lays the groundwork for Kreĭn-like theorems associated with the CHH bifurcation that are more rigorously discussed in our companion chapter \cite{chaptII}.

math-ph↗