Physical design of FEL injector based on the performance-enhanced EC-ITC RF gun

To meet the requirements of high performance THz-FEL （Free Electron Laser）, a compact scheme of FEL injector was proposed. A thermionic cathode was chosen to emit electrons instead of a photo-cathode with its complex structure and high cost. The effective bunch charge was improved to ~200 pC by adopting an enhanced EC-ITC （External Cathode Independently Tunable Cells） RF gun to extract micro-bunches; back bombardment effects were almost eliminated as well. Constant gradient accelerator structures were designed to improve energy to ~14 MeV, while the focusing system was applied for emittance suppressing and bunch state maintenance. The physical design and beam dynamics of the key components for the FEL injector were analyzed. Furthermore, start- to-end simulations with multi-pulses were performed using homemade MATLAB and Parmela. The results show that continual high brightness electron bunches with a low energy spread and emittance could be obtained stably.     

Production,installation and test of Nb-sputtered QWRs for ALPI

Eight cryostats, each housing 4 sputtered Nb/Cu, 160 MHz, quarter wave resonators (QWR), are now in operation in ALPI[1]. Two of them house high β cavities; the others are equipped with medium β resonators. Another medium β cryostat is ready and will be installed in the early 2002. Pb/Cu medium β accelerating cavities are now present only in four cryostats and they will have their Pb superconducting (SC) layer replaced by sputtered Nb soon. The substitution of the Pb SC layer in ALPI medium β resonators did not interfere with ALPI operation; the upgrading of resonators went on parallel to the cryostat maintenance programme. The average accelerating field of these resonators, at the design power of 7 W, overcomes 4 MV/m, whereas, when Pb electroplated, their average value was 2.7 MV/m. The sputtered resonator combines the good SC characteristics of Nb with the higher thermal conductivity and better stability to change of He bath pressure, which is typical of copper resonators. This leads to a very high reliability, as routinely experienced during beam acceleration.     

重离子冷却储存环CSRm双电子复合实验研究类锂36,40Ar15+离子同位素移动

配备电子冷却装置的重离子储存环为开展高电荷态离子的双电子复合（dielectronic recombination,DR）精密谱学研究提供了绝佳的实验平台。本工作在兰州重离子加速器冷却储存环主环（HIRFL-CSRm）上开展了类锂36,40Ar15+离子的双电子复合实验,实验观测了电子-离子质心系能量范围为0~35 eV的双电子复合速率系数谱。通过外推法获得了36,40Ar15+离子2s_1/2→2p_1/2和2s_1/2→2p_3/2的跃迁能量。同时利用GRASP2K程序理论计算了36,40Ar15+离子2s_1/2→2p_1/2和2s_1/2→2p_3/2跃迁的质量移动因子和场移动因子,进而得到双电子复合谱的同位素移动值。36,40Ar15+离子2s_1/2→2p_1/2和2s_1/2→2p_3/2同位素移动分别为0.861 meV和0.868 meV。它们均小于目前CSRm上双电子复合实验的实验分辨为~10 meV,进而解释了实验测量的DR谱上未能观察到同位素移动的原因。然而,高电荷态离子的同位素移动场效应与原子序数Z5成正比,因此,在重离子加速器冷却储存环实验环（HIRFL-CSRe）以及未来大型加速器--强流重离子加速器装置（HIAF）上有望通过DR精密谱学方法研究高电荷态重离子甚至放射性离子的同位素移动,进而获得相关原子核的核电荷半径等信息。The cooler storage ring is equipped with an electron-cooler. It is an excellent experimental platform for dielectronic recombination (DR) experiment of highly-charged ions. In this paper, the dielectronic recombination experiments of lithium-like Ar15+ ions with mass number 36 and 40 are conducted at the HIRFL-CSRm(main ring of the Cooling Storage Ring of Heavy Ion Research Facility in Lanzhou). The experimental electron-ion collision energy scale is from 0 eV to 35 eV. Extrapolation method is exploited to obtain the excitation energies of transitions 2s_1/2→2p_1/2 and 2s_1/2→2p_3/2 of the 36,40Ar15+ ions from experimental data. Meanwhile, GRASP2K program is utilized to calculate the mass shift factors and field shift factors of 36,40Ar15+ ions for 2s_1/2→2p_1/2 and 2s_1/2→2p_3/2 transitions to obtain isotope shifts in DR spectra. In theoretical calculation, isotope shifts of 36,40Ar15+ ions corresponding to 2s_1/2→2p_1/2 and 2s_1/2→2p_3/2 are 0.861 meV and 0.868 meV, respectively. They are both less than the experimental precision (~10 meV) of these dielectronic recombination experiments at the CSRm, which explains that isotope shifts cannot be distinguished from the experimental dielectronic recombination spectra. However, the field shift of highly-charged ions is proportional to Z5. In the future, the dielectronic recombination experiments of highly-charged heavy ions even radioactive ions will be conducted at the HIRFL-CSRe (experimental ring of the Cooling Storage Ring of Heavy Ion Research Facility in Lanzhou) and the future large accelerator facility--HIAF(High intensity Heavy-ion Accelerator Facility) to measure isotope shifts to obtain the nuclear charge radius information.     

远离稳定线原子核的实验研究（Ⅰ）

综述了近年来我国在远离稳定线原子核实验研究中取得的重要进展．这些实验研究工作主要是在中国科学院近代物理研究所（ＩＭＰ）、中国原子能科学研究院（ＣＩＡＥ）和中国科学院上海原子核研究所（ＳＩＮＲ）进行的．文章还简要介绍了ＩＭＰ和ＣＩＡＥ现有加速器上研制的放射性束流线及进一步的发展计划．     

兰州冷却环总体设计

兰州重离子冷却环CSR是兰州重离子加速器研究装置HRRFL的一项升级工程, 是一个双冷却储存环系统,由主环CSRm和实验环CSRe构成. 从HIRFL回旋加速器系统来的重离子束, 首先注入到主环CSRm中进行累积冷却, 然后加速到较高的能量引出打初级靶产生放射线次级束RIBs或高离化重离子束, 这些次级束再被送到验环CSRe储存起来以开展内靶实验.     

HIRFL-CSR团簇靶的优化

为HIRFL-CSR团簇内靶设计加工了新的供气系统, 拆换了原有的喷嘴, 对氢气和氩气进行了新的实验, 获得了氢气和氩气的稳定团簇束, 解决了困扰团簇靶稳定运行的喷嘴堵塞问题. 获得的氢团簇束密度为1.75×10¹³ atoms/cm³, 好于德国GSI内靶对氢束所达到的1×10¹³atoms/cm³. 研究了团簇束的衰减, 测量了氢束和氩束的有效靶厚, 研究了团簇靶系统对这两种工作气体的长期运行稳定性. 对氢和氩两种工作气体, 各级气压呈现了良好的稳定性, 说明在实验的时间范围内, 团簇靶运行稳定.     

兰州重离子加速器的状态和发展

文章首先简要地介绍了世界上重离子加速器的发展状态,然后对兰州重离子加速器（HRFL）的结构,建造过程,运行情况,多年来以及目前正在进行的主要改造项目进行了描述,为适应核物理及其相关学科的持续发展研究的需要,对HIRFL近期和将来的发展情况作了概括的描述。     

Beam dynamics simulations of the injector for a compact THz source

Terahertz radiation has broad application prospects due to its ability to penetrate deep into many organic materials without the damage caused by ionizing radiations. A free electron laser （FEL）-based THz source is the best choice to produce high-power radiation. In this paper, a 14 MeV injector is introduced for generating high-quality beam for FEL, is composed of an EC-ITC RF gun, compensating coils and a travelling-wave structure. Beam dynamics simulations have been done with ASTRA code to verify the design and to optimize parameters. Simulations of the operating mode at 6 MeV have also been executed.     

Laser Cooling and Spectroscopy of Relativistic C^{3+} Beams at the ESR

We report on the first laser cooling of a bunched beam of multiply charged ions performed at the ESR (GSI) at a beam energy of GeV. Moderate bunching provided a force counteracting the decelerating laser force of one counterpropagating laser beam. This versatile type of laser cooling lead to longitudinally space-charge dominated beams with an unprecedented momentum spread of . Concerning the beam energy and charge state of the ion, the experiment depicts an important intermediate step from the established field of laser cooling of ion beams at low energies toward the unique laser cooling scheme proposed for relativistic beams of highly charged heavy ions at SIS 300 (FAIR). Funded by the German BMBF under contract number 06ML183.     

Statistical theory of hot nuclei and high spin states

The hot rotating compound systems formed in heavy ion collisions are studied using the statistical theory with a view to determine the spin and temperature dependence of nuclear shapes. Shape transitions are observed for these systems at particular spin values. The neutron and proton separation energies for heavier high spin systems have been evaluated. Results are presented for ₇₀ ¹⁷⁰ Yb and ₇₈ ¹⁹⁴ Pt.     

Conditioning of BPM pickup signals for operations of the Duke storage ring with a wide range of single-bunch current

The Duke storage ring is a dedicated driver for the storage ring based oscillator free-electron lasers（FELs）, and the High Intensity Gamma-ray Source（HIGS）. It is operated with a beam current ranging from about1 mA to 100 mA per bunch for various operations and accelerator physics studies. High performance operations of the FEL and γ-ray source require a stable electron beam orbit, which has been realized by the global orbit feedback system. As a critical part of the orbit feedback system, the electron beam position monitors（BPMs） are required to be able to precisely measure the electron beam orbit in a wide range of the single-bunch current. However, the high peak voltage of the BPM pickups associated with high single-bunch current degrades the performance of the BPM electronics, and can potentially damage the BPM electronics. A signal conditioning method using low pass filters is developed to reduce the peak voltage to protect the BPM electronics, and to make the BPMs capable of working with a wide range of single-bunch current. Simulations and electron beam based tests are performed. The results show that the Duke storage ring BPM system is capable of providing precise orbit measurements to ensure highly stable FEL and HIGS operations.     

原子核质量精密测量的研究进展

原子核质量的精密测量是原子核物理学的重要课题之一,它对探索奇特原子核的结构和性质、重元素核合成之谜等均具有重大意义.文章简要介绍了原子核质量高精度测量的两个主要设备——储存环和潘宁阱,并回顾了近年来原子核质量精密测量在核结构、元素核合成、新同核异能素等领域中的研究亮点,探讨原子核质量测量的发展趋势.     

The Utilization of Low Frequency Raman Spectra of Gases for the Study of Molecules with Large Amplitude Vibration

The utilization of the Raman spectra of the low frequency bending mode for three quasi-linear molecules: disiloxane,(SiH3)2O;methylisocyanate,CH3NCO;and dimethylisocyanate,(CH3)2SiHNCO for observing the low frequency anharmonic bending vibration is demonstrated which is superior to the corresponding far infrared spectra.From the observed frequencies from the Raman spectra the potential function governing the heavy atom motion to linearity has been obtained from which the barrier has been determined.These experimental values are compared to the ab initio predicted values.Also low frequency Raman spectra of the ring puckering vibration of chlorocyclobutane,c-C4H7Cl,bromocyclobutane,c-C4H7Br,and aminocyclobutane,c-C4H7NH2,have been utilized to obtain the potential function governing the ring inversion for these molecules.The determined barriers to planarity are compared to those obtained from MP2(full) ab initio and density functional theory B3LYP calculations by utilizing a variety of basis sets.For all of these studies it is shown that the Raman spectra are superior to the infrared spectra for determining the frequencies of the excited state transitions.     

Photodissociation spectroscopy of OH+ molecular ions at the TSR storage ring

When infrared active molecular ions are stored in a heavy ion storage ring, a fast beam of vibrationally and rotationally relaxed molecules can be obtained. This opens up new opportunities for various experimental studies in molecular ion physics, particularly those involved with spectroscopy and dissociation dynamics of excited states. The analysis of such experiments is facilitated by the fact that the information on the initial states is able to identify and, therefore, eliminate them from the assignment problem. Moreover, when the intensity of the measured transitions is monitored as a function of storage time, the dependence of these processes on the degree of internal relaxation is revealed. We demonstrate these general principles by application to near threshold dissociation spectroscopy of the OH⁺ molecular ion. The structure of quasibound levels near the dissociation limit of OH⁺ and its dissociation energy are deduced. This revised version was published online in August 2006 with corrections to the Cover Date.     

Some of the current trends in the studies of sputtering

Abstract

The main directions in experimental, theoretical and computer studies of sputtering of solids under ion bombardment are analyzed. It is emphasized that there is a close relation between these studies and practical applications of sputtering.     

Linear optics calibration and nonlinear optimization during the commissioning of the SSRF storage ring

Phase I commissioning of the SSRF storage ring on 3.0 GeV beam energy was started at the end of December 2007. A lot of encouraging results have been obtained so far. In this paper, calibrations of the linear optics during the commissioning are discussed, and some measured results about the nonlinearity given. Calibration procedure emphasizes correcting quadrupole magnetic coefficients with the Linear Optics from Closed Orbit (LOCO) technique. After fitting the closed orbit response matrix, the linear optics of the four test modes is substantially corrected, and the measured physical parameters agree well with the designed ones.     

Design and first commissioning of a new mode with lower emittance in the SSRF storage ring

A new mode is designed with an emittance of 2.47 nm-rad at 3.0 GeV beam energy, lower than the nominal mode of the Shanghai Synchrotron Radiation Facility (SSRF) storage ring. Details of the linear optics design and the nonlinear optimization are presented in this paper. During Phase I commissioning of the storage ring we tested the new optics mode and some expected results were obtained. After restoring the linear optics by means of the linear optics with closed orbit technique, the main parameters of the real machine agree well with the designed values and the injection efficiency and beam lifetime are acceptable.     

Calculation of energy density in the colour tube model of relativistic heavy ion collisions

The energy density produced in a relativistic heavy ion collision is calculated within the framework of the colour tube model. The chromoelectric field generated in the collision produces quark-antiquark pairs. The motion of these particles is described by Boltzmann equation. The interaction between the quarks and antiquarks is approximated by introducing a relaxation time.     

Development of the PHENIX silicon pixel detector

The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) is being upgraded with a novel four-layer silicon vertex tracker. The detector will enhance the physics capabilities of PHENIX in the future phase of the heavy-ion and the polarized proton-proton programs at RHIC. The silicon vertex tracker will allow the direct measurement of heavy quark production by identifying displaced decay vertices, and will reconstruct jets with nearly full azimuthal coverage over |η| < 1.2. We are developing a novel Silicon Pixel Detector for the inner two barrel layers of the silicon vertex tracker. In this paper, the status of the development is reported. for the PHENIX collaboration Presented in the Poster Session “Future Experiments and Facilities” at the 18th International Conference “Quark Matter 2005”, Budapest, Hungary, 4–9 August 2005.