Special-purpose radiation sources based on the Siberia-2 storage ring

Synchrotron radiation (SR) generated by homogeneous magnetic fields of bending magnets is now employed at the Siberia-2 electron storage ring. It is planned that, in the near future, most of the storage ring’s free straight sections will be equipped with insertion devices (undulators and wigglers). Two projects of specialized radiation sources based on the Siberia-2 stor age ring are discussed. The first source is a vacuum milliundulator intended for generation of extremely bright X-ray beams. An X-ray source with vertically limited diffraction is shown to be feasible when the vertical emittance of an electron beam is equal to the diffraction emittance of photons with an energy of 2 keV. The second source uses edge radiation (ER) generated at the ends of bending magnets of the storage ring. Calculations show that, in the infrared and ultraviolet spectral regions, the ER intensity must exceed the intensity of standard SR formed by the homogeneous field of a bending magnet.     

Permanent magnet wigglers for reducing the emittance of the Petra III synchrotron radiation source

The Petra III synchrotron radiation source was developed based on the Petra-II 6-GeV electron accelerator (DESY). After installing the system for radiation damping, the horizontal emittance of the electron beam of Petra III decreased from 5 nm rad to 1 nm rad, which is a record parameter for this class of installations. The system of radiation damping includes 20 permanent magnet wigglers installed in two straight sections, 50 m each. The total radiation power of the wigglers reaches 800 kW. The wigglers used in the radiation damping system of Petra III were developed in collaboration with DESY (Hamburg) and fabricated by the Budker Institute of Nuclear Physics. The wiggler length is 4.04 m, the gap between the poles is 24 mm, the maximum magnetic field is B = 1.52?1.56 T, and the period is λ = 20 cm. This paper describes the design features of the permanent magnet wigglers and the methods and results of adjustment of the wiggler operating parameters.     

扭摆器中的微束团不稳定性

用理论和数值的方法, 首次研究了扭摆器中相干同步辐射效应诱发的微束团不稳定性. 这一不稳定性只存在于小能散的情况, 并当电子能量或峰值磁场取特定值时, 不稳定度达到最大值. 在BFEL的扭摆器中, 可能有轻微的不稳定性存在; 在CTF的扭摆器中, 则不会有不稳定性发生.     

I. Synchrotron radiation from the large electron-positron storage ring LEP

The properties of synchrotron radiation from LEP are investigated. This radiation from LEP are investigated. This radiation is assumed to be in a parasitic mode without changing any of the operating parameters. At 86 GeV the radiation from the normal bending magnet has a critical energy of 0.4 MeV and a power of ～500 W/m, and is probably of limited interest. High photon energies (10–20 MeV) of high intensity can be obtained from normal and superconducting wiggler magnets. Undulators can give quasi-monochromatic radiation of high brightness with photon energies of up to 5 MeV. New magnet developments might increase this energy range. Quasi-monochromatic γ-rays of ～100 MeV can be created with soft Compton back scattering without disturbing the electron bean. This relies on future free electron lasers in the submillimetre range. The natural collimation, the polarization and the time structure make all these photon beams unique tools for research in nuclear physics. The synchrotron rediation can be used to produced photoneutrons with intensities of up to 10¹⁴ neutrons/s. It is foreseen that LEP will be equipped with superconducting cavities in later stage and that is energy will be increased to ～130 GeV. This will approximately double the photon energies obtained from wigglers and undulators.     

Numerical experiments on free-electron lasers without inversion

The inversionless free-electron laser having a drift region consisting of two magnets is analyzed. Performing numerical simulations of electron motion inside wigglers and the drift region, we have shown that this system has a positive mean gain over the entire energy distribution of the electron beam. We study the influence of emittance and the spread of electron energies on the gain.     

The Paternity of the H-Bombs: Soviet-American Perspectives

There are major problems in the history of the American and Soviet hydrogen bombs. They are associated with the Teller-Ulam and Teller-Oppenheimer controversies, and the question of whether the design of the Soviet H-bomb was an independent conception. Because of the scarcity of documentary evidence, these problems have little chance of being settled if the histories of the two are considered separately within their national frameworks. Considered comparatively, however, they can help clarify these problems separately and convert them into different facets of this most important segment in the history of the thermonuclear age.The recently disclosed evidence on the history of the Soviet H-bomb, in particular, on Klaus Fuchs’s key idea of radiation implosion, validates Edward Teller’s view on the invention of the H-bomb, including his understatement of his own accomplishment and his concern about the benefits and head start that the Soviet H-bomb program could have gotten from Fuchs’s espionage. In addition, the Russian perspective on the realities of illusory worlds during the Cold War helps us see these illusory worldviews as largely responsible for the intensity of the H-bomb debate in the United States. Gennady Gorelik is a research fellow in the Center for Philosophy and History of Science at Boston University and is the author of biographies of Matvei Bronstein and Andrei Sakharov.     

High-gain FEL with variable parameter wigglers

A general discussion of FEL with variable parameter wigglers for the production of high power coherent radiation at reasonable efficiency is presented. Some promising modes are identified and analyzed.     

Study of lower emittance dedicated synchrotron radiation mode for the BEPCⅡ

In this paper,a dedicated synchrotron radiation (SR) mode for the BEPCⅡ with an emittance of 85 nm has been designed,including the linear lattice,chromaticity correction and dynamic aperture optimization.The emittance of the new mode is about 60% of the previous mode used for routine operation of the BEPCⅡ .The effect of wigglers on the linear lattice was compensated and the total dynamic aperture including the wigglers’ nonlinear effect was estimated.The preliminary commissioning at the end of 2008 and the formal operation with the new mode confirmed its merits.     

Commissioning experience with insertion devices at PETRA III

PETRA III is a new hard X-ray synchrotron radiation source, operating at 6 GeV with a beam current of up to 100 mA and extremely low horizontal emittance of 1 nm rad. Such low emittance is achieved by using two 100 m long damping wiggler sections which reduce the emittance by a factor of 4. Altogether the damping sections contain 20 wigglers of 4m length each. The emitted synchrotron radiation power produced by wigglers amounts to 420 kW at 100 mA beam current in total. In the new octant of PETRA III, there are 14 undulator beamlines, with a brilliance up to 10²¹ (s mrad² mm² 0.1% BW)⁻¹ which cover an energy range from 0.3 keV to more than 100 keV. The low emittance raises very high requirements to the field quality of the insertion devices. At first, it should not affect the positron beam trajectory. Secondly, the spectral properties of the radiation created, like the intensity of higher harmonics, should not be limited by the undulator field quality, but by the beam emittance effects in order to have some reserve for future machine upgrades or possible radiation demagnetization. This paper presents the current status of PETRA III insertion devices and describes intermediate commissioning results like impact of IDs on the positron beam orbit or photon beam and radiation problems.     

Physics design of SSRF synchrotron radiation security

High brightness of SSRF brings about synchrotron radiation security problems, which will be solved in physics design. The main radiations are generated from bending magnets and insertion devices. Since the fact that radiation power and radiating area are different in these two kinds of synchrotron radiation, the arrangements of photon absorbers, diaphragms and other vacuum components need to be treated distinctively. In addition, SSRF interlock protection threshold is defined and the beam orbit in the straight line is limited. Hence, beam orbit in the bending magnets and IDs are also restricted by the threshold. The orbit restriction is calculated and helps us to arrange the vacuum components. In this paper, beam orbit distortion restricted by interlock protection threshold, radiation power, radiation angle and illuminating area are calculated. From the calculation results, the physics designs in manufacture and installation vacuum components are put forward. By commissioning, it is shown that physics requirements are met rigidly in the engineering process.     

紧凑型自由电子激光THz源上四极磁铁的设计及测量

基于自由电子激光（FEL）的太赫兹源具有高功率、高效率、波谱范围宽且连续可调、波束质量好等显著优点,目前是获得最高输出功率的方法。紧凑型太赫兹源使整体装置小型化,减少了装置成本和占用空间,但依然可以提供高功率、高品质的太赫兹波束,是一种便利可靠的用户装置。由于空间限制,FEL上的磁铁要尽可能地减小其尺寸,并仍能满足束流参数设计要求。本文设计的四极磁铁磁轭孔径与有效长度,其中2块是64 mm100 mm,另外3块是45 mm100 mm。这些四极磁铁的磁场梯度可以达到0.6~1.9 Tm-1。采用Poisson和Oprra-3D软件进行四极磁铁的二维和三维仿真计算,设计优化四极磁铁的结构,并测量了加工完成后的四极磁铁的磁场。     

Nonlinear harmonic generation in free-electron lasers with helical wigglers

It is widely believed that harmonics are suppressed in helical wigglers. However, linear harmonic generation (LHG) occurs by an azimuthal resonance that excites circularly polarized, off-axis waves, where the hth harmonic varies as exp((ihtheta). Nonlinear harmonic generation (NHG) is driven by bunching at the fundamental and has different properites from LHG. While NHG has been studied in planar wigglers, there has been no analysis of NHG in helical wigglers. The 3D simulation code medusa has been modified for this purpose, and it is shown that NHG is substantial in helical wigglers and that the even and odd harmonics have comparable intensities.     

Adventures with Synchrotron Radiation at Harvard

In the late 1950s, a 6 GeV electron synchrotron (the CEA) was being built at Harvard/MIT. Ed Purcell, who generally trafficked in volts (or maybe kilovolts), but never gigavolts, was thinking about what one could do with all that synchrotron radiation that otherwise would uselessly warm up the walls of the beamline (I remember well his student Roger Tsien's nice drawing of radiation from kinks in the outgoing E-field lines of an electron in relativistic circular motion; see Figure 1).     

Physics design of SSRF synchrotron radiation security

High brightness of SSRF brings about synchrotron radiation security problems, which will be solved in physics design. The main radiations are generated from bending magnets and insertion devices. Since the fact that radiation power and radiating area are different in these two kinds of synchrotron radiation, the arrangements of photon absorbers, diaphragms and other vacuum components need to be treated distinctively. In addition, SSRF interlock protection threshold is defined and the beam orbit in the straight line is limited. Hence, beam orbit in the bending magnets and IDs are also restricted by the threshold. The orbit restriction is calculated and helps us to arrange the vacuum components. In this paper, beam orbit distortion restricted by interlock protection threshold, radiation power, radiation angle and illuminating area are calculated. From the calculation results, the physics designs in manufacture and installation vacuum components are put forward. By commissioning, it is shown that physics requirements are met rigidly in the engineering process.     

Reduction of the beam emittance in the charged-particle storage rings with the help of periodic magnetic wigglers

Periodic magnetic structures (wigglers) have been successfully used for a long time for controlling beam parameters in charged-particle storage rings for various purposes (including the reduction of emittance). In this work, we optimize the optical functions of the storage ring gap into which a wiggler is installed for a more effective reduction of the emittance. Optimal solutions are obtained for the first time for FODOtype and theoretical minimum emittance (TME) structures. An original method is proposed for suppressing the contribution of the wiggler fields to the radiation excitation of the phase volume of the beam by modulating the field period along the wiggler axis.     

2维全自动亥姆霍兹线圈磁块测量方法

在波荡器和扭摆器的研制过程中,为提高磁块的测量效率和精度,提出了2维全自动亥姆霍兹线圈磁块测量方法。通过理论推导得到仅采用2维全自动旋转而不需要3维旋转就可以实现磁块的全自动测量,降低了磁块全自动测量的实现难度。根据该方法的理论,已成功研制出一台2维全自动亥姆霍兹线圈测量装备,并在上海光源的磁块测量中使用。系统地给出2维全自动亥姆霍兹线圈磁块的测量理论和方法,并对测量误差进行了分析,该系统实现了磁块剩磁测量的高效率、高精度和高重复性,可以在30 s内完成单磁块的测量,重复性和精度均好于510-4。     

2维全自动亥姆霍兹线圈磁块测量方法

在波荡器和扭摆器的研制过程中,为提高磁块的测量效率和精度,提出了2维全自动亥姆霍兹线圈磁块测量方法。通过理论推导得到仅采用2维全自动旋转而不需要3维旋转就可以实现磁块的全自动测量,降低了磁块全自动测量的实现难度。根据该方法的理论,已成功研制出一台2维全自动亥姆霍兹线圈测量装备,并在上海光源的磁块测量中使用。系统地给出2维全自动亥姆霍兹线圈磁块的测量理论和方法,并对测量误差进行了分析,该系统实现了磁块剩磁测量的高效率、高精度和高重复性,可以在30 s内完成单磁块的测量,重复性和精度均好于510-4。     

Alvin Van Valkenburg and the diamond anvil cell

Abstract

As many of you may know already, Alvin Van Valkenburg died on December 5, 1991 in Tucson, Arizona at the age of seventy-eight. He was the last surviving scientist of four who share the honor of co-inventing the diamond anvil high pressure cell (DAC), now recognized as a world-class instrument for scientific research. In August of 1992 Professor A. Ruoff asked me to write a short article for AIRAPT describing Van Valkenburg's role in inventing the DAC because of its importance as a tool in high pressure research. He suggested that as a former colleague and as a scientist who has spent most of his professional career in high pressure research, I was perhaps the one person who could describe best the role Van Valkenburg played in the invention and development of the DAC. After some deliberation, I agreed to do it, mainly for three reasons: (1) the subject matter, indeed, is important to the history of science, and, in particular, to the high pressure community and should be documented; (2) all four co-inventors deserve the honor; and (3) it is true perhaps that there is no one more appropriate to undertake this task because I was at the National Bureau of Standards, NBS, (now the National Institute of Standards and Technology, NIST) at the time and personally witnessed the process of the invention of the DAC.     

Sm_2Co_(17)型永磁合金的辐照效应研究

Sm_2Co_(17)型永磁合金大量使用在上海同步辐射光源储存环的永磁型波荡器上,在受到长期辐照后会发生磁性能损失的现象,进而影响同步辐射光的品质.为了探索其潜在的微观机理,本文首先对Sm_2Co_(17)型永磁合金所处混合辐射场的粒子及相关物理量进行了计算分析,确定引发磁性能损失的主要粒子是中子.然后采用Ar离子模拟中子辐照损伤的方法对其进行辐照,采用透射电镜对其辐照前后的微观形貌及微观结构进行了研究探讨,采用振动样品磁强计对永磁合金辐照前后的饱和磁化强度进行了分析对比,并讨论了微观结构演化与宏观磁性能变化的联系.结果表明,Ar离子辐照后Sm_2Co_(17)型永磁合金饱和磁化强度的不可逆损失与微观结构变化有直接的关系,其2:17相从单晶结构转变为非晶结构是造成其磁性能损失可能的微观机制.     

上海同步辐射装置储存环注入冲击磁铁的设计

 开展了上海同步辐射装置储存环注入冲击磁铁的结构和脉冲电源的技术设计,并进行了磁场分布和励磁电流波形的模拟计算。还给出了陶瓷真空盒镀膜的设计参数,提出了计算陶瓷真空盒镀膜接受同步光功率的公式,研究了防止镀膜和波纹管受到同步光照射的机械布局设计。