Comparison of SOLPS5.0 and SOLPS-ITER simulations for ASDEX upgrade L-mode

This paper examines the backward compatibility of SOLPS-ITER with SOLPS5.0 and produces a basic test of the physics/numerics improvements/additions in SOLPS-ITER recommended by developers, taking an ASDEX Upgrade L-mode simulation as an example. SOLPS-ITER, which is emerging as the most advanced tool for edge plasma modelling, can be instructed to mimic SOLPS5.0 physics/numerics. This allows producing a detailed comparison of the two codes, in a framework where they are expected to produce the similar results, thus raising the confidence in using SOLPS-ITER to continue SOLPS5.0 simulations. Under such framework, SOLPS-ITER results match well with those of SOLPS5.0. The remaining differences might be from the ion energy source, and a full benchmark activity is expected to solve this in the future. We then test the effect of the recommended physics/numerics introduced in SOLPS-ITER with respect to the widely used SOLPS5.0. Only deuterium shots are considered as the basic test, where the recommended physics/numerics are simple and expected not to change the simulation results significantly. Electron density and temperature on divertor targets are the key metrics in this study, instead of particle fluxes and power load. Numerical simulations show that the effect of the recommended physics/numerics on the final solution results in only ∼5% differences in the outer mid-plane and target profiles of electron density and temperature. An upstream density scan, covering the full range from attached to detached conditions, also produces closely matching results (∼10% differences). Thus, we believe that recommended physics/numerics do not introduce unwanted spurious effects and are confident about future modelling results of SOLPS-ITER.     

A One‐Dimensional Particle‐in‐Cell Model of Plasma Build‐Up in Vacuum Arcs

Understanding the mechanism of plasma build‐up in vacuum arcs is essential in many fields of physics. A one‐dimensional particle‐in‐cell computer simulation model is presented, which models the plasma developing from a field emitter tip under electrical breakdown conditions, taking into account the relevant physical phenomena. As a starting point, only an external electric field and an initial enhancement factor of the tip are assumed. General requirements for plasma formation have been identified and formulated in terms of the initial local field and a critical neutral density. The dependence of plasma build‐up on tip melting current, the evaporation rate of neutrals and external circuit time constant has been investigated for copper and simulations imply that arcing involves melting currents around 0.5–1 A/μm², evaporation of neutrals to electron field emission ratios in the regime 0.01 – 0.05, plasma build‐up timescales in the order of ～ 1 – 10 ns and two different regimes depending on initial conditions, one producing an arc plasma, the other one not. Also the influence of the initial field enhancement factor and the external electric field required for ignition has been explored, and results are consistent with the experimentally measured local field value of ～ 10 GV/m for copper (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Collisions between molecules in the <Emphasis Type="Italic">J</Emphasis> = 0 state

Collisions between electrostatically trapped molecules in the J = 0 state are theoretically investigated. Molecules in this state are advantageous for the evaporative cooling, because inelastic collision is impossible at ultra-low temperature. However, inelastic collision is more significant than elastic collision at high temperature, because the off-diagonal dipole matrix elements are much larger than the diagonal elements. The elastic and inelastic collision cross-sections are calculated under the condition that the collisional kinetic energy is larger than the energy gap between the rotational states. The dependencies of the collision cross-sections on the collisional kinetic energy and molecular constants are examined.Received: 29 July 2004, Published online: 21 September 2004PACS: 31.15.Qg Molecular dynamics and other numerical methods - 33.80.Ps Optical cooling of molecules; trapping - 33.90. + h Other topics in molecular properties and interactions with photons     

Site‐specific fabrication of graphitic microporous carbon terminated with ordered multilayer graphene walls

The site‐specific fabrication of metal‐incorporated graphitic microporous carbon terminated by highly ordered multilayer graphene walls via an ambient‐temperature vacuum‐based process is presented for the first time. Sputtering of Cr nano‐particles on the ultrathin amorphous carbon film manifests a dual effect of activation via dry‐etching by the sputtering plasma and of ‘knock‐on' inelastic collision between nanoparticles and C atoms for structural ordering. This novel and simple method is very useful for fabricating high surface area carbon nanostructures for hydrogen storage and clean energy applications. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An alternative scheme of angular‐dispersion analyzers for high‐resolution medium‐energy inelastic X‐ray scattering

The development of medium‐energy inelastic X‐ray scattering optics with meV and sub‐meV resolution has attracted considerable efforts in recent years. Meanwhile, there are also concerns or debates about the fundamental and feasibility of the involved schemes. Here the central optical component, the back‐reflection angular‐dispersion monochromator or analyzer, is analyzed. The results show that the multiple‐beam diffraction effect together with transmission‐induced absorption can noticeably reduce the diffraction efficiency, although it may not be a fatal threat. In order to improve the efficiency, a simple four‐bounce analyzer is proposed that completely avoids these two adverse effects. The new scheme is illustrated to be a feasible alternative approach for developing meV‐ to sub‐meV‐resolution inelastic X‐ray scattering spectroscopy.     

Nonregular phenomena in systems of quantum wells in the presence of tunneling processes

The effect of tunneling on inelastic processes in atomic collision physics has been studied using two examples: head-on collision between hydrogen atoms and protons and hydrogen-atom reflection from an impenetrable wall. These phenomena are analyzed using the numerical solution of the nonstationary Schr?dinger equation.     

Collisions between electrostatically confined linear polar molecules

Collisions between linear polar molecules that were electrostatically trapped were investigated. The collisional transition from a low to a high field seeking state (inelastic collision) causes trap loss. The efficiency of evaporative cooling is improved at higher elastic collision rates. We calculated cross-sections of inelastic and elastic collision using a semi-classical treatment. Received 6 December 2001 / Received in final form 26 February 2002 Published online 28 June 2002     

Modulation‐Based Atom‐Mirror Entanglement and Mechanical Squeezing in an Unresolved‐Sideband Optomechanical System

A hybrid optomechanical system which is composed of an atomic ensemble and a standard optomechanical cavity driven by a periodically modulated external laser field is investigated. Based on the simple periodic modulation forms of the driving amplitude and effective optomechanical coupling, respectively, the atom‐mirror entanglement is discussed in detail. It is found that the maximum of the entanglement in the unresolved‐sideband regime can be further enhanced compared with the non‐modulation regime. On the other hand, we find that the introduction of the atomic ensemble permits the mechanical squeezing induced by the periodic amplitude modulation can be successfully generated even in the unresolved‐sideband regime. Due to the self‐cooling mechanism constructed by the atomic ensemble, the mechanical squeezing scheme no longer requires the extra precooling technologies.     

Eigen electromagnetic waves of a coaxial waveguiding structure filled by a non‐uniform dissipative plasma with azimuthal magnetic field

This paper studies the propagation and spatial attenuation of high‐frequency eigen‐symmetric and dipolar electromagnetic waves along a coaxial plasma–metal waveguiding structure that contains a slightly axial and strong radial non‐uniform cylindrical plasma slab in an external azimuthal non‐uniform magnetic field. The influence of such parameters as the effective electron collision frequency, the direct current value producing the external azimuthal magnetic field, parameters that characterize plasma density radial profile, and waveguide geometric parameters on the dispersion, spatial attenuation, and radial field structure of the waves is considered. The regions of waveguiding structure parameters where the electromagnetic wave properties can be effectively controlled are studied and analyzed.     

Method for Finding the Exact Effective Hamiltonian of Time‐Driven Quantum Systems

Time‐driven quantum systems are important in many different fields of physics as cold atoms, solid state, optics, etc. Many of their properties are encoded in the time evolution operator or the effective Hamiltonian. Finding these operators usually requires very complex calculations that often involve some approximations. To perform this task, a systematic scheme that can be cast in the form of a symbolic computational algorithm is presented. It is suitable for periodic and non‐periodic potentials and, for convoluted systems, can also be adapted to yield numerical solutions. The method exploits the structure of the associated Lie group and a decomposition of the evolution operator on each group generator. To illustrate the use of the method, five examples are provided: harmonic oscillator with time‐dependent frequency (Paul trap), modulated optical lattice, time‐driven quantum oscillator, a step‐wise driving of a free particle, and the non‐periodic Caldirola‐Kanai Hamiltonian. To the extent of the authors' knowledge, whereas the exact form of Paul trap's evolution operator is well known, its effective Hamiltonian was until now unknown. The remaining four examples accurately reproduce previous results.     

Invariant‐Based Pulse Design for Three‐Level Systems Without the Rotating‐Wave Approximation

In this paper, a scheme is put forward to design pulses which drive a three‐level system based on the reverse engineering with Lewis‐Riesenfeld invariant theory. The scheme can be applied to a three‐level system even when the rotating‐wave approximation (RWA) can not be used. The amplitudes of pulses and the maximal values of detunings in the system could be easily controlled by adjusting control parameters. We analyze the dynamics of the system by an invariant operator, so additional couplings are unnecessary. Moreover, the approaches to avoid singularity of pulses are studied and several useful results are obtained. We hope the scheme could contribute to fast quantum information processing without RWA.     

Triple-collision operator for a quantum gas with bound states

The triple-collision operator of dense gas theory is analyzed for a quantum-mechanical gas obeying Boltzmann statistics. The contribution of two-body bound states is extracted by using Faddeev's representation of the three-body resolvent. The result is a binary atom-molecule collision operator which includes the effects of molecular formation and breakup, and inelastic and rearrangement collisions. An additional contribution is a modification of the Boltzmann collision operator due to the binding of one member of the colliding pair to a third particle. The analysis is carried out in the framework of the Green-Kubo formulas so the operators considered are linear and the results are in a form suitable for the evaluation of the transport coefficients.     

Impurity in a Maxwellian unforced granular fluid

We investigate velocity statistics of an impurity immersed in a uniform granular fluid. We consider the cooling phase, and obtain scaling solutions of the inelastic Maxwell model analytically. First, we analyze identical fluid-fluid and fluid-impurity collision rates. We show that light impurities have similar velocity statistics as the fluid background, although their temperature is generally different. Asymptotically, the temperature ratio increases with the impurity mass, and it diverges at some critical mass. Impurities heavier than this critical mass essentially scatter off a static fluid background. We then analyze an improved inelastic Maxwell model with collision rates that are proportional to the average fluid-fluid and fluid-impurity relative velocities. Here, the temperature ratio remains finite, and the system is always in the light-impurity phase. Nevertheless, ratios of sufficiently high-order moments / may diverge, a consequence of the multiscaling asymptotic behavior.     

双温度通道电弧等离子体二维数值模拟

本文对圆形通道内双温度等离子体的传热与流动特性进行了二维数值模拟,研究中假定体系处于局域化学平衡态,但电子温度不等于重粒子温度,需分别用各自的守恒方程求解．采用数值实验的方法对电子-重粒子非弹性碰撞过程进行了研究,计算结果表明,数值模拟中对非弹性碰撞过程不同的处理方法(α的不同取值)会影响计算预测的等离子体特性．α的合适数值,需要在今后的研究工作中进一步将计算结果与实验测量结果比较来加以确定。     

Global Existence of Classical Solutions to the Inelastic Vlasov–Poisson–Boltzmann System

We study the global existence and uniqueness of classical solutions to the inelastic Vlasov–Poisson–Boltzmann system for a soft potential in the near vacuum regime. For the global existence of classical solutions, we assume reasonable conditions on the restitution coefficient, which represents the character of inelastic collisions. We use the smallness of initial data and an algebraically decaying weight function in the spatial variable to control the self-consistence force and collision operator.     

Inelastic collisional effect on a dilute granular shock layer with a heated wall

The inelastic collisional effect on a shock layer of a dilute granular gas with a heated wall is numerically studied. To investigate the inelastic collisional effect via the gain term in the inelastic Boltzmann equation on the shock layer, an inelastic Bhatnagar-Gross-Krook (BGK) type equation, whose loss term is equivalent to that in the inelastic Boltzmann equation, is formulated on the basis of the kinetic theory of the granular gas. The inelastic BGK-type equation formulated for a hard-sphere particle is generalized to that for an inverse power law (IPL) molecule. Numerical results in a weakly inelastic regime confirm the nonequilirium contribution to the cooling rate, when the collision frequency depends on the particle velocity. The profile of the negative high-velocity tail of the distribution function in the generation regime of the shock wave obtained by the Direct Simulation Monte Carlo method is higher than that obtained by the proposed BGK-type equation when the collision frequency depends on the particle velocity because of the inelastic collisional effect via the gain term in the inelastic Boltzmann equation, which is not included in the proposed BGK-type equation.     

非均匀等离子体湍流的重正化准线性理论——Misguich-Balescu理论的推广

本文把Misguich和Balescu建立的均匀等离子体湍流的重正化准线性理论推广到非均匀等离子体湍流。在弱耦合和弱非均匀性近似下,得到传播算符和平均湍性碰撞算符的明晰表达式。非均匀性除对算符中的扩散贡献、共振加宽或频移、Dupree衰减和平均分布函数在速度空间的陡度效应等作出一定的修正之外,还引出新的指数微分算符:在传播算符中是涨落电场关联函数非均匀性导致的新的速度微分算符,在平均湍性碰撞算符中是平均分布函数非均匀性导致的新的空间微分算符。平均分布函数非均匀性还使得在平均湍性碰撞算符中出现的两个互为逆运算的自由流传播算符不能抵消,从而使包含在(直接作用于平均分布函数的)传播算符中的非马尔可夫效应显露出来。 关键词：     

A large‐solid‐angle X‐ray Raman scattering spectrometer at ID20 of the European Synchrotron Radiation Facility

An end‐station for X‐ray Raman scattering spectroscopy at beamline ID20 of the European Synchrotron Radiation Facility is described. This end‐station is dedicated to the study of shallow core electronic excitations using non‐resonant inelastic X‐ray scattering. The spectrometer has 72 spherically bent analyzer crystals arranged in six modular groups of 12 analyzer crystals each for a combined maximum flexibility and large solid angle of detection. Each of the six analyzer modules houses one pixelated area detector allowing for X‐ray Raman scattering based imaging and efficient separation of the desired signal from the sample and spurious scattering from the often used complicated sample environments. This new end‐station provides an unprecedented instrument for X‐ray Raman scattering, which is a spectroscopic tool of great interest for the study of low‐energy X‐ray absorption spectra in materials under in situ conditions, such as in operando batteries and fuel cells, in situ catalytic reactions, and extreme pressure and temperature conditions.