Visible and invisible in physical theory

The following question is considered: How is it that physicists can invent equations, so rich in structure, so detailed in consequences, and so closely in agreement with experience?     

Relativistic solenoids

We construct a general relativistic analogy of an infinite solenoid, i.e., of an infinite cylinder with zero electric charge and non-zero electric current in the direction tangential to the cylinder and perpendicular to its axis. We further show that the solution has a good weak-field limit.Dedicated to Prof. Jií Horáek on the occasion of his 60th birthday.     

Casimir force between two Aharonov-Bohm solenoids

The vacuum structure for the massive charged scalar field in the region of two parallel, infinitely long and thin solenoids confining the fluxesn ₁ andn ₂ is studied. By using the Green function method, it is found that the vacuum expectation value of the system's energy has a finite mutual interaction term depending on the distance a between the solenoids, which implies an attractive force per unit length given by F _n1n2 =–(c/²)(n ₁ n ₂)²/a ³.     

Matching by solenoids in space charge dominated LEBTs

The betatron matching of a rotationally asymmetric beam in space charge dominated low-energy beam transports (LEBTs) where solenoids are used for the transverse matching has been studied.For better understanding, the coupling elements of a beam matrix are interpreted in special forms that are products of a term defined by the Larmor rotation angle and another by the difference between the beam matrix elements in the two transverse planes.The coupling form originally derived from the rotationally symmetric field in solenoids still holds when taking into account the rotationally asymmetric space charge forces that are due to the unequal emittance in the two transverse planes.It is shown in this paper that when an LEBT mainly comprising solenoids transports a beam having unequal emittance in the two transverse planes and the linear space charge force is taken into account, the initial Twiss parameters can be modified to obtain the minimum and equal emittance at the LEBT exit.The TRACE3D calculations also prove the principle.However, when quadrupoles that are also rotationally asymmetric are involved in between solenoids, the coupling between the two transverse planes becomes more complicated and the emittance increase is usually unavoidable.A matching example using the CSNS (China Spallation Neutron Source) LEBT conditions is also presented.     

Multi-window invisible cloaks

This paper reports that a general method of designing invisible cloaks is using variant constitutive material parameters to realize the space transformation. A hollow region can be hidden after this transformation. It was recently shown (Ma H, Qu S B, Xu Z and Wang J F 2009 \wx{Appl. Phys. Lett.}{94} 103501) that when the original point moves to the boundary of a cloak, the cloak can be designed to be open. Based on this theory, we propose multi-window invisible cloaks which can conceal a group of objects. Full wave simulations for invisible cloaks with regular and irregular shapes verified this method.     

Zero modes in a periodic system of Aharonov-Bohm solenoids

The existence of infinitely degenerate zero modes is proved for a quantum-mechanical two-dimensional charged particle with spin 1/2 moving in the field of an infinite system of Aharonov-Bohm solenoids. The condition for appearance of these modes is found and their explicit form is obtained.     

一种多层螺线管电感计算拟合公式（英）

提出了一种多层螺线管线圈电感的精确计算方法,其思想是叠加螺线管单层线圈的自感和不同线圈层之间的互感。建立了用于计算单层线圈自感的显示表达理论模型,给出了两层线圈之间互感的数值计算方法。使用提出的精确算法,计算出一个实验中使用的螺线管线圈的电感为4.30 mH,与实验测量的电感值4.33 mH的偏差小于1%。     

Matching by solenoids in space charge dominated LEBTs

The betatron matching of a rotationally asymmetric beam in space charge dominated low-energy beam transports （LEBTs） where solenoids are used for the transverse matching has been studied. For better understanding, the coupling elements of a beam matrix are interpreted in special forms that are products of a term defined by the Larmor rotation angle and another by the difference between the beam matrix elements in the two transverse planes. The coupling form originally derived from the rotationally symmetric field in solenoids still holds when taking into account the rotationally asymmetric space charge forces that are due to the unequal emittance in the two transverse planes. It is shown in this paper that when an LEBT mainly comprising solenoids transports a beam having unequal emittance in the two transverse planes and the linear space charge force is taken into account, the initial Twiss parameters can be modified to obtain the minimum and equal emittance at the LEBT exit. The TRACE3D calculations also prove the principle. However, when quadrupoles that are also rotationally asymmetric are involved in between solenoids, the coupling between the two transverse planes becomes more complicated and the emittance increase is usually unavoidable. A matching example using the CSNS （China Spallation Neutron Source） LEBT conditions is also presented.     

一种多层螺线管电感计算拟合公式（英）

提出了一种多层螺线管线圈电感的精确计算方法,其思想是叠加螺线管单层线圈的自感和不同线圈层之间的互感。建立了用于计算单层线圈自感的显示表达理论模型,给出了两层线圈之间互感的数值计算方法。使用提出的精确算法,计算出一个实验中使用的螺线管线圈的电感为4.30 mH,与实验测量的电感值4.33 mH的偏差小于1%。     

Calculation of the static magnetic field of a system of solenoids

We propose a variant of the algorithm described in [1], which allows one to calculate the magnetic field of a solenoid with rectangular cross section by using one numerical quadrature.     

Fast invisible neutrino decays

Any value for the lifetime of neutrinos decaying into invisible modes (another neutrino and a Goldstone boson) is possible in theories in which the lepton number is a spontaneously broken global symmetry with different charges for every family. There are two types of models. Only in one of them neutrinos could, in a natural way, be relevant for cosmology.     

Generation of pulse magnetic fields in multilayer solenoids with prestressed turns

In the present paper a new design is proposed of multilayer Cu-wire wound solenoids, which is based on the reduction of the radial pressure due to magnetic forces by the counter-pressure of the prestressed banding. Such solenoids are capable of generating stronger magnetic fields than those of present design. The extent of their applicability is estimated.The author wishes to express his thanks to J.Kaczér Dr. Sc. for valuable advice and discussions on the problem described.     

Realization of a locally-round beam in an ultimate storage ring using solenoids

"Ultimate" storage rings (USRs), with electron emittance smaller than 100 pm·rad and on the scale of the diffraction limit for hard X-rays in both transverse planes, have the potential to deliver photons with much higher brightness and higher transverse coherence than that projected for the rings currently operational or under construction. Worldwide efforts have been made to design and to build light sources based on USRs. How to obtain a round beam, i.e., a beam with equivalent transverse emittances, is an important topic in USR studies. In this paper, we show that a locally-round beam can be achieved by using a pair of solenoid and anti-solenoid with a circularly polarized undulator located in between. Theoretical analysis and application of this novel method, particularly to one of the Beijing Advanced Photon Source storage ring design having natural emittance of 75 pm·rad, are presented.     

Analysis of a conformal invisible device

We perform a semi-analytical calculation of the field distributions of a conformal invisible device via mode expansions. For a discrete set of frequencies in the regime of wave optics, the conformal invisible device is perfectly transparent, which stems from the special conformal mapping and the refractiveindex profile of the Mikaelian lens.     

电磁超散射和隐形门

基于变换光学的幻象光学器件能够表现出自然界中不存在的现象,如隐身、超散射和隐形门等。其中电磁超散射现象利用变换光学中的折叠几何变换,使得物体的散射截面远大于其几何截面,颠覆了人们对于传统散射中散射截面通常小于散射体几何截面的认知。这一现象也为现实中实现“穿墙术”提供了可能。文章着重介绍了基于变换光学的超散射的发展历程以及利用超散射实现隐形门的方法。隐形门在自由空间的实现为将来幻象器件的设计提供了新的思路。     

2.0T斜螺线管型超导二极磁体设计

基于一种新型的斜螺线管型线圈结构,我们设计了一台2.0T超导二极磁体样机。该磁体由4层斜螺线管线圈组成,工作电流为2960A。线圈孔径为40mm,其中好场区达到了孔径的2/3。由于线圈形状的特殊性,其端部结构无需优化,各高阶谐波量沿轴向积分为零。文中介绍了斜螺线管型线圈的特点和原理,借助两种电磁场分析软件,完成了超导二极磁体的磁场设计,最后简要介绍磁体的加工情况。