新一代多电荷态离子源的研究

离子源发展存在两大热点问题：其一强流高电荷态离子的产生；其二强流金 属离子的产生。为了获得强流高电荷态离子，我们设计制造了全超导 ECR 离子 源 SECRAL（Superconducting ECR ion source with Advanced design in Lanzhou） ， 该离子源采用了全新的超导磁体结构形式，工作于 18～28GHz 的微波频率。根据 scaling laws 和实验经验，我们确定了 SECRAL 离子源所需要的约束磁场场形， 并针对新的磁体结构设想，通过 TOSCA 程序进行了详细的计算，成功地设计出 满足我们场形要求的超导磁体物理模型。据此，我们进一步进行了超导磁体的力 学结构分析，为磁体机械工艺设计提供了参考依据，保证了超导磁体结构设计的 可靠性。源体建成后，经过一系列的测试和调束实验，不但验证了我们的设计和 分析是合理的、可靠的，而且创造了许多项束流调试的新世界纪录，我们分别获 得了 810 A eμ O7+ 、730 A eμ Ar 11+ 、220 A eμ Ar 14+ 、73 A eμ Ar 16+ 、483 A eμ Xe 20+ 等束 流。为了获得强流中低电荷态金属离子束，我们尝试探索一种原理、结构、工作 模式全新的离子源－外部电子注入PIG离子源（E-PIG） 。目前，我们基本按照我 们的初期设想设计建造了 E-PIG离子源，设计中采用了外部电子枪注入电子、空 心阴极、特殊的场形等手段来提高金属离子的电荷态和流强。经过初步的起弧调 试，我们发现在初期的设计中还存在一些问题亟待进一步整改。

ECR等离子体的轫致辐射谱和极紫外光研究

本论文对电子回旋共振（ECR）等离子体发出的轫致辐射谱和极紫外光做了系统的实验研究，并对ECR等离子体的工作机制及新的应用前景进行了探索。 在ECR等离子体中，热电子对于离子的形成、约束以及整个等离子体的能量平衡具有重要意义，而由电子发出的轫致辐射谱则包含了电子的能量、密度等信息，因此，测量等离子体发出的轫致辐射谱作为一种非侵入式的诊断方式，成为等离子体诊断的有力手段。为了研究ECR等离子体中热电子这个重要组成部分，我们对三台高电荷态ECR离子源的轫致辐射谱进行了系统测量，并通过对实验谱的拟合得到一个代表等热电子平均能量的参量——光谱温度Tspe。通过测量不同工作参数下（例如微波频率、功率，约束磁场，掺气，负偏压等）等离子体的轫致辐射谱，深入研究了ECR离子源的这些工作参数对热电子能量及密度的影响，并对ECR等离子体中与电子加热及等离子体约束相关的一些物理问题进行了探索性的研究和讨论，在此基础上，对一些已在ECR离子源界得到广泛应用但其物理机制尚不十分清晰的经验性规律及技巧（如Scaling laws，掺气效应，负偏压效应等），做出了新的解释。其中的创新点有：通过对ECR等离子体轫致辐射谱的测量，首次从电子加热的角度诠释了在ECR源领域得到普遍认可的有关约束磁场的Scaling laws；首次实验观察到在磁场分量Blast≈Bext时，离子源的约束和引出之间的关系达到最佳，而当Bext小于Blast较多时，等离子体的约束将遭到较严重的破坏；实验观察到热电子能量随共振区磁场梯度的减弱而提高，并分别从单粒子轨道模型和电磁波在等离子体中的传播两个角度对这一现象进行了分析；基于实验现象，从抑制等离子体不稳定性的角度出发对掺气效应做出了新的解释。 由于在未来光刻及显微成像等领域的广泛应用前景，极紫外（EUV）和软X射线光源目前是国际上的研究热点，而ECR等离子体作为一种高离化态的等离子体，为EUV和软X射线光源的发展提供了一条新思路。为了研究ECR等离子体作为EUV光源的可行性，我们对其发出的波长在13.5nm附近的窄带宽EUV光功率进行了初步测量，在超导ECR离子源——SECRAL上，测量到了超过2W的窄带宽EUV光功率（2π sr），这是目前国际上利用ECR等离子体产生并测量到的EUV光功率中的最好结果，这一结果证明了ECR等离子体作为EUV光源的潜力，但在发射强度、转化效率等方面还需做出很大的改进，本论文给出了相应的研究发展思路

高电荷态ECR离子源的设计与实验研究

本文详细论述了三种各具特色的高电荷态ECR离子源的设计与研制，它们分别是：14．SGHz全永磁高电荷态ECR离子源LAPEC咫、传统常温ECR离子源GTS、混和超导ECR离子源HECRIS。另外，还从理论与实验两个方面对ECR离子源多电荷态离子束流的引出进行了详细研究。设计研制了一台高性能14．SGHz全永磁ECR离子源LAPECRZ，该离子源的设计尺寸为杯50mm*560mm，重量可达9ookg以上，为目前世界上体积与重量最大、设计参数最高的全永磁ECR离子源。全永磁离子源的尺寸增大一些，其加工与研制所存在的难度将会有质的变化。研制LAPEC形所存在的技术难度大大超过了以往所有全永磁ECR离子源。LAPECR2的磁场参数为：注入磁场1 ．4T，如果加注入端辅助铁扼，磁场可达2．6T；引出磁场为1 ．1T；六极永磁体在弧腔内壁产生的最大径向磁场的设计值为1．22T，实际加工得到的磁场大小为1．2T，与计算结果基本一致。该离子源的设计采用了多种特殊技术与方法以提高引出高电荷态离子束流强度，如：双层含铝衬底的等离子体弧腔、铝制等离子体电极、冷阴极电子枪（注入端负偏压电极）、旁轴微波直接馈入与等离子体位置相对于磁场可调等等。目前，我们已开始源体的组装。GTS离子源为目前世界上运行性能最好的常温ECR离子源之一。它的设计指导思想是ECR离子源的经验结论scaling Laws，高磁场、高磁镜比，高磁场梯度是该离子源磁场设计的主要特点。设计时充分考虑了多频加热机制，允许多频功率同时馈入弧腔：IOGHz＋14GHz＋18GHz＋ZSGHz。良好的磁场约束、灵活的磁场结构设计、高频率大功率微波馈入、大体积弧腔、足够的冷二次电子注入、优良的真空抽气系统、以及有效的束流引出系统等等都是该离子源高性能表观的原因。经过近一年半的优化与调试，该离子源运行性能优良，能产生很多领先国际伺类ECR源的离子束流，如：1.95emAO6+，O·semAArll”，o．15e拜AArl犷，31Oe瘩建叙e，哪se拼A豁岁”与0.4eμAXe39+为18GHz时调试的结果：1.OemAAr8+，1.8eμAAr17+24OeμAXe20+ ，20eμAxe30+与0.3oe从Axe38＋为在14GHz调试的最好结果。该离子源已多次为原子物理实验提供了Ar17+与Ar18+等高电荷态离子束流。HECRIS是一台高性能混和超导ECR离子源，其各项设计参数均高于GTS源，以保证该离子源能具有比GTS更好的性能。它的最小B场型设计继续沿袭现在ECR离子源设计惯用的Scaling Laws设计思想。该离子源采用较高频率的微波馈入，设计运行范围为18GHz-24GHz。该离子源着重于在运行调试中实现对轴向最小磁场Bmin的调节与匹配，这里采用两组超导线包进行辅助调节。径向磁约束由一个能在弧腔内壁产生1．6T径向磁场的六极永磁体提供，它强磁场设计与部分磁块存在的退磁问题的解决也是该离子源的一大特点与难点。文中还详细讨论一个高性能的Halbach结构六极永磁体的设计方法。分别从永磁材料选取、物理尺寸优化、结构选择等角度，结合理论分析与PolssON，PERMAG和TOscA3D程序的模拟计算结果，对六极永磁体的性能进行了全面的分析，提出两种确定六极永磁体中存在退磁磁块的办法，并且提出了一种用高极化矫顽力永磁材料替代退磁磁块中所采用的永磁材料的解决办法。对多电荷态ECR离子源的引出进行了理论与实验两方面的研究。利用PBGUNS程序，对ECR离子源的引出系统进行了一定的理论分析。通过模拟计算，详细地论述了引出系统的各主要物理参数对ECR离子源引出离子束流品质的影响。这些得到的结果，对设计一套高性能的ECR离子源引出系统具有一定的指导意义。结合理论分析，我们还设计完成了一系列关于ECR离子源引出系统的实验，来研究多电荷态离子束流的引出与短距离传输。采用电扫描发射度测量系统（ESS）探测离子束流在x与y方向的发射度，用两个荧光靶分别在束运线不同位置探测束流的束斑形状，并利用一个亮度探测器对束斑相对亮度进行探测。通过多组实验结果的处理，分别分析了离子源的几个主要参数如磁场、微波、掺气、偏压等对引出束流品质的影响并结合相关理论给予了解释，通过对混合多电荷态离子束流的三电极引出实验结果的讨论，建立了一个关于高电荷态ECR离子源束流引出的较为清晰的物理图象。

How does solvent molecular size affect the microscopic structure in polymer solutions?

Monte Carlo simulation has been used to investigate the effects of linear solvent molecular size on polymer chain conformation in solutions. Increasing the solvent molecular size leads to shrinkage of the polymer chains and increase of the critical overlap concentrations. The root-mean-square radius of gyration of polymer chains (R-g) is less sensitive to the variation of polymer concentration in solutions of larger solvent molecules. In addition, the dependency of R-g on polymer concentration under normal solvent conditions and solvent molecular size is in good agreement with scaling laws. When the solvent molecular size approaches the ideal end-to-end distance of the polymer chain, an extra aggregation of polymer chains occurs, and the solvent becomes the so-called medium-sized solvent. When the size of solvent molecules is smaller than the medium size, the polymer chains are swollen or partially swollen. However, when the size of solvent molecules is larger than the medium size, the polymer coils shrink and segregate, enwrapped by the large solvent molecules.

How optimal life history changes with the community size-spectrum

This paper derives optimal life histories for fishes or other animals in relation to the size spectrum of the ecological community in which they are both predators and prey. Assuming log-linear size-spectra and well known scaling laws for feeding and mortality, we first construct the energetics of the individual. From these we find, using dynamic programming, the optimal allocation of energy between growth and reproduction as well as the trade-off between offspring size and numbers. Optimal strategies were found to be strongly dependent on size spectrum slope. For steep size spectra (numbers declining rapidly with size), determinate growth was optimal and allocation to somatic growth increased rapidly with increasing slope. However, restricting reproduction to a fixed mating season changed optimal allocations to give indeterminate growth approximating a von Bertalanffy trajectory. The optimal offspring size was as small as possible given other restrictions such as newborn starvation mortality. For shallow size spectra, finite optimal maturity size required a decline in fitness for large size or age. All the results are compared with observed size spectra of fish communities to show their consistency and relevance.

Numerical simulation of the charge balance in an EBIT

The electron beam ions traps (EBITs) are widely used to study highly charged ions (HCIs). In an EBIT, a high energy electron beam collides with atoms and ions to generate HCIs in the trap region. It is important to study the physics in the trap. The atomic processes, such as electron impact ionisation (EI), radiative recombination (RR), dielectronic recombination (DR) and charge exchange (CX), occur in the trap and numerical simulation can give some parameters for design, predict the composition and describe charge state evolution in an EBIT [Phys. Rev. A 43 (199 1) 4861]. We are presently developing a new code, which additionally includes a description of the overlaps between the ion clouds of the various charge-states. It has been written so that it can simulate experiments where various machine parameters (e.g. beam energy and current) can vary throughout the simulation and will be able to use cross- sections either based on scaling laws or derived from atomic structure calculations. An object-oriented method is used in developing the new software, which is an efficient way to organize and write code. (C) 2003 Elsevier Science B.V. All rights reserved.

A simple model of atomic interactions in noble metals based explicitly on electronic structure

A total energy tight-binding model with a basis of just one s state per atom is introduced. It is argued that this simplest of all tight-binding models provides a surprisingly good description of the structural stability and elastic constants of noble metals. By assuming inverse power scaling laws for the hopping integrals and the repulsive pair potential, it is shown that the density matrix in a perfect primitive crystal is independent of volume, and structural energy differences and equations of state are then derived analytically. The model is most likely to be of use when one wishes to consider explicitly and self-consistently the electronic and atomic structures of a generic metallic system, with the minium of computation expense. The relationship to the free-electron jellium model is described. The applicability of the model to other metals is also considered briefly.

Dielectronic recombination in He-like, Li-like, and Be-like highly charged ions in the KLL and KLM manifolds

This paper reports a systematic study of the dependence on atomic number of the dielectronic recombination resonance strengths for He-like, Li-like and Be-like ions. Recent measurements of dielectronic recombination resonance strengths for the KLL and KLM manifolds for iron, yttrium, iodine, holmium, and bismuth are also described. The resonance strengths were normalized to calculated electron impact ionization cross sections. The measured resonance strengths generally agree well with theoretical calculations using the distorted wave approximation. However, KLM resonance strength measurements on high atomic number open-shell ions gave higher values than those suggested by calculations. Using recently measured data, along with existing results, scaling laws have been generated as a function of atomic number for He-like, Li-like, and Be-like ions in the KLL and KLM manifolds.

HTS Motors in Aircraft Propulsion: Design Considerations

Current high temperature superconducting (HTS) wires exhibit high current densities enabling their use in electrical rotating machinery. The possibility of designing high power density superconducting motors operating at reasonable temperatures allows for new applications in mobile systems in which size and weight represent key design parameters. Thus, all-electric aircrafts represent a promising application for HTS motors. The design of such a complex system as an aircraft consists of a multi-variable optimization that requires computer models and advanced design procedures. This paper presents a specific sizing model of superconducting propulsion motors to be used in aircraft design. The model also takes into account the cooling system. The requirements for this application are presented in terms of power and dynamics as well as a load profile corresponding to a typical mission. We discuss the design implications of using a superconducting motor on an aircraft as well as the integration of the electrical propulsion in the aircraft, and the scaling laws derived from physics-based modeling of HTS motors.

Characterization and parametrization in terms of atomic number of x-ray emission from K-shell filling during ion-surface interactions

When highly charged ions are incident on a surface, part of their potential energy is emitted as characteristic radiation. The energies and yields of these characteristic x rays have been measured for a series of elements at the Tokyo electron-beam ion trap. These data have been used to develop a simple model of the relaxation of the hollow atoms which are formed as the ion approaches the surface, as well as a set of semiempirical scaling laws, which allow for the ready calculation of the K-shell x-ray spectrum which would be produced by an arbitrary slow bare or hydrogenlike ion on a surface. These semiempirical scaling laws can be used to assess the merit of highly charged ion fluorescence x-ray generation in a wide range of applications.

ON THE UNIVERSALITY OF 2-DIMENSIONAL DIFFUSION-LIMITED DEPOSITION

A history dependent stick probability is introduced to the diffusion-limited deposition model. The exponents in the scaling laws are calculated. The universality class is also discussed.

Analytical approximations to numerical solutions of theoretical emission measure distributions

Emission line fluxes from cool stars are widely used to establish an apparent emission measure distribution, EmdApp(Te), between temperatures characteristic of the low transition region and the low corona. The true emission measure distribution, EmdTrue(Te), is determined by the energy balance and geometry adopted and, with a numerical model, can be used to predict EmdApp(Te), to guide further modelling. The scaling laws that exist between coronal parameters arise from the dimensions of the terms in the energy balance equation. Here, analytical approximations to numerical solutions for EmdTrue(Te) are presented, which show how the constants in the coronal scaling laws are determined. The apparent emission measure distributions show a minimum value at some T0 and a maximum at the mean coronal temperature Tc (although in some stars, emission from active regions can contribute). It is shown that, for the energy balance and geometry adopted, the analytical values of the emission measure and electron pressure at T0 and Tc depend on only three parameters: the stellar surface gravity and the values of T0 and Tc. The results are tested against full numerical solutions for e Eri (K2 V) and are applied to Procyon (a CMi, F5 IV/V). The analytical approximations can be used to restrict the required range of full numerical solutions, to check the assumed geometry and to show where the adopted energy balance may not be appropriate. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Acceleration of ions up to 20MeV/nucleon in the ultrashort, high-intensity regime

The measurements reported here provide scaling laws for the ion acceleration process in the regime of ultrashort (50 fs), ultrahigh contrast (10) and ultrahigh intensity (> 10W/cm ), never investigated previously. The scaling of the accelerated ion energies was studied by varying a number of parameters such as target thickness (down to 10nm), target material (C and Al) and laser light polar- ization (circular and linear) at 35° and normal laser incidence. A twofold increase in proton energy and an order of magnitude enhancement in ion flux have been observed over the investigated thickness range at 35° angle of incidence. Further- more, at normal laser incidence, measured peak proton energies of about 20 MeV are observed almost independently of the target thickness over a wide range (50nm- 10 µm). 1. © 2012 by Società Italiana di Fisica.

Collectively enhanced optomechanical coupling in periodic arrays of scatterers

We investigate the optomechanical properties of a periodic array of identical scatterers placed inside an optical cavity and extend our previous results. We show that operating at the points where the array is transmissive results in linear optomechanical coupling strengths between the cavity field and collective motional modes of the array that may be several orders of magnitude larger than is possible with an equivalent reflective ensemble. We describe and interpret these effects in detail and investigate the nature of the scaling laws of the coupling strengths for the different transmissive points in various regimes. © 2013 American Physical Society.

Modelling the brightness increase signature due to asteroid collisions

We have developed a model to predict the post-collision brightness increase of sub-catastrophic collisions between asteroids and to evaluate the likelihood of a survey detecting these events. It is based on the cratering scaling laws of Holsapple and Housen (2007) and models the ejecta expansion following an impact as occurring in discrete shells each with their own velocity. We estimate the magnitude change between a series of target/impactor pairs, as- suming it is given by the increase in reflecting surface area within a photometric aperture due to the resulting ejecta. As expected the photometric signal increases with impactor size, but we find also that the photometric signature decreases rapidly as the target aster- oid diameter increases, due to gravitational fallback. We have used the model results to make an estimate of the impactor diameter for the (596) Scheila collision of D = 49 − 65m depending on the impactor taxonomy, which is broadly consistent with previous estimates. We varied both the strength regime (highly porous and sand/cohesive soil) and the tax- onomic type (S-, C- and D-type) to examine the effect on the magnitude change, finding that it is significant at early stages but has only a small effect on the overall lifetime of the photometric signal. Combining the results of this model with the collision frequency estimates of Bottke et al. (2005), we find that low-cadence surveys of ∼one visit per luna- tion will be insensitive to impacts on asteroids with D < 20km if relying on photometric detections.