Institutional Repository of Institute of Modern Physics, CAS
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Time-of-flight detectors with improved timing performance for isochronous mass measurements at the CSRe
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">In isochronous mass spectrometry (IMS) established in heavy-ion storage rings the revolution times of the stored secondary ions should be independent of their velocity spread. However, this isochronous condition is fulfilled only in first order and in a small range of revolution times. To correct for the non-isochronicity an additional measure of the velocity or magnetic rigidity of each stored ion is required. For this purpose two new time-of-flight (TOE) detectors were installed in a straight section of the experimental Cooler Storage Ring CSRe in Lanzhou. The performance of the new time-of-flight (TOF) detectors, which is crucial for the achievable efficiencies and mass resolving power, was significantly improved. The time resolution of the TOE detector in offline tests was sigma = 18.5 +/- 2 ps. The detector setup was put into operation with a stable beam of Kr-78. (C) 2014 Elsevier B.V. All rights reserved.</span
X-ray spectrum emitted by the impact of Xe-129(26+) of the different kinetic energies on Au surface
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">The characteristic X-ray spectra produced by the impact of Xe-129(26+) with kinetic energies from 350 to 600 keV and from 1.8 to 3.9 MeV on Au surface are measured. It is found that Xe-129(26+) with kinetic energies from 350 to 600 keV can excite only the characteristic X-ray spectra of M alpha of Au, but Xe-129(26+) with kinetic energies from 1.8 to 3.9 MeV can excite the characteristic X-ray spectra of M zeta, M alpha, M gamma and M delta. The relation between the characteristic X-ray intensity, the ratio of X-ray yield and the ion kinetic energy is analyzed. The kinetic energy threshold of L-X-ray of Xe emitted by Xe26+ is estimated.</span
一米长四翼型RFQ调谐研究
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">为获取ADS工程中四翼型RFQ加速器在设计、调谐和运行等方面的经验, 设计和建造了一台一米长四翼型RFQ加速器。该RFQ的设计频率为162.5 MHz, 但是测量结果显示即使没有调谐器时, 腔体的频率也为163.7 MHz。为降低腔体频率, 使用四线模型理论进行了分析并重新设计了腔体的端板。使用了二极模稳定杆来加大四极频率与相邻二极频率的间隔。最终测量结果显示, 在腔体电压分布没有大的波动的情况下腔体频率达到了设计频率。同时, 腔体Q值降低了1%, 这就要求需要更多的功率注入腔体。使用水对二极模稳定杆进行了冷却, 以便腔体能够稳定工作。</span><span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">In order to get experiences of design, tuning and running of a four-vane RFQ for the China ADS pro ject, a one-meter four-vane RFQ was designed and fabricated. The quadruple frequency of the RFQ was designed to be 162.5 MHz (operating frequency), but the measured frequency after fabrication was 163.7 MHz even without tuners in the cavity. To reduce the frequency the four-wire line model theory was used, and the endplates were redesigned. Dipole mode stabilizer rods were employed to expand the span of the quadruple frequency and the adjacent dipole frequency. As a result, the quadruple frequency was altered to the operating frequency without rippling voltage distribution along the RFQ severely. Meanwhile, the Q value was reduced by 1%, which means more RF power was required to be fed into the RFQ. The dipole mode stabilizer rods were cooled by water to make the RFQ work stably.</span
Charge and frequency resolved isochronous mass spectrometry and the mass of Co-51
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">Revolution frequency measurements of individual ions in storage rings require sophisticated timing detectors. One of common approaches for such detectors is the detection of secondary electrons released from a thin foil due to penetration of the stored ions. A new method based on the analysis of intensities of secondary electrons was developed which enables determination of the charge of each ion simultaneously with the measurement of its revolution frequency. Although the mass-over-charge ratios of Co-51(27+) and Ar-34(18+) ions are almost identical, and therefore, the ions cannot be resolved in a storage ring, by applying the new method the mass excess of the short-lived Co-51 is determined for the first time to be ME(Co-51) = -27 342(48) keV. Shell-model calculations in the fp-shell nuclei compared to the new data indicate the need to include isospin-nonconserving forces. (C) 2014 The Authors. Published by Elsevier B.V.</span
Novel determination of density, temperature, and symmetry energy for nuclear multifragmentation through primary fragment-yield reconstruction
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">For thefirst time primary hot isotope distributions are experimentally reconstructed in intermediate heavy-ion collisions and used with antisymmetrized molecular dynamics (AMD) calculations to determine density, temperature, and symmetry energy coefficient in a self-consistent manner. A kinematical focusing method is employed to reconstruct the primary hot fragment-yield distributions for multifragmentation events observed in the reaction system Zn-64 + Sn-112 at 40 MeV/nucleon. The reconstructed yield distributions are in good agreement with the primary isotope distributions of AMD simulations. The experimentally extracted values of the symmetry energy coefficient relative to the temperature, a(sym)/T, are compared with those of the AMD simulations with different density dependence of the symmetry energy term. The calculated a(sym)/T values change according to the different interactions. By comparison of the experimental values of a(sym)/T with those of calculations, the density of the source at fragment formation was determined to be rho/rho(0) = (0.63 +/- 0.03). Using this density, the symmetry energy coefficient and the temperature are determined in a self-consistent manner as a(sym) = (24.7 +/- 1.9) MeV and T = (4.9 +/- 0.2) MeV.</span
Heavy-ion radiography facility at the Institute of Modern Physics
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">In order to identify the density and material type, high energy protons, electrons, and heavy ions are used to radiograph dense objects. The particles pass through the object, undergo multiple coulomb scattering, and are focused onto an image plane by a magnetic lens system. A modified beam line at the Institute of Modern Physics of the Chinese Academy of Sciences has been developed for heavy-ion radiography. It can radiograph a static object with a spatial resolution of about 65 mu m (1 sigma). This paper presents the heavy-ion radiography facility at the Institute of Modern Physics, including the beam optics, the simulation of radiography by Monte Carlo code and the experimental result with 600 MeV/u carbon ions. In addition, dedicated beam lines for proton radiography which are planned are also introduced.</span
Design of Low Energy Beam Transport System for CSRe Molecular Ion Research Facility
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">本文完成了 CSRe分子离子研究装置低能传输线的物理设计。采用Poisson/Superfish软件对150 kV倍压型高压加速器的电场分布进行了模拟,结果显示,加速器各区域空间电场强度均远低于击穿电场强度限值。利用Beampath程序对离子源引出的分子离子束在高压加速器中的传输进行了模拟,束流包络显示,加速区电场对分子离子束具有较强的聚焦作用,加速管出口束斑尺寸较小。采用Trace-3D 程序设计了高分辨能力的磁分析系统和RFQ加速器的注入匹配段。通过Beampath程序的模拟,分析出了质量数为150的分子离子束,并由三单元四极透镜实现了分析束流与直线加速器RFQ的注入匹配。</span><span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">The design of a low energy beam transport system for CSRe molecular ion research facility was presented. The electric field distribution of the 150 kV high voltage accelerator was simulated by Poisson/Superfish code. The results show that the electric field strengths of various region spaces were far lower than the value of breakdown electric field. The transmission of the molecular ion beam from the ion source was simulated by Beampath in the high voltage accelerator. The beam envelope indicates that the electric field of acceleration section has a strong focusing effect on the molecular ion beam, and the beam size is small at the end of the accelerate tube. The Trace-3D code was used to design the magnetic analysis system with high resolution and the matching section for injecting into RFQ accelerator. Finally, through the simulation, the molecular ion beam with the mass number of 150 was analyzed and the injection matching of the RFQ accelerator by one triplet quadrupoles was achieved.</span
Study on space charge effect in an electrostatic ion analyzer applied to measure laser produced ions
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">The abundance of different ions produced by laser ion sources is usually analyzed by an electrostatic ion analyzer (EIA). Ion current intensities in the range of several mA/cm(2) at the position of the EIA have been achieved from the laser ion source developed by the Institute of Modern Physics; this indicates that a noticeable influence of space charge effect during the ion transmission will occur. Hence, while the parameters of the EIA or the beams are changed, such as ion species, current intensity, the ions' transmission efficiency through the EIA is different, which will result in an uncertainty in the estimation of the ions' yields. Special attention is focused on this issue in this paper. Ion's transmissions through the EIA under different circumstances are studied with simulations and experiments, the results of which are consistent with each other. (C) 2014 AIP Publishing LLC.</span
