Latest progress of the RFQ cooler and buncher RFQ1L

The RFQ cooler and buncher RFQ1L is a key device of the SHANS (Spectrometer for Heavy Atoms and Nucleax Structure). The status of the machining and assembly of the central part is introduced, and the structure of the whole RFQ1L system and the preliminary plan for the testing are discussed also.

Experimental study of the high-voltage breakdown and simulations for the RFQ cooler and buncher RFQ1L

The RFQ cooler and buncher RFQ1L is one of the key parts of the being-built super-heavy nuclide research spectrometer. In order to understand the high-voltage breakdown phenomenon, the voltages between electrodes have been measured. In addition, more extensive simulations have been performed for better understanding and optimizing the RFQ1L work points.

Progress on the RFQ1L and LPT

The SHANS spectrometer is under construction in the Institute of Modern Physics, Chinese Academy of Science. The RFQ cooler and buncher RFQ1L is one of the key devices in the SHANS. To perform direct mass measurement, the Lanzhou Penning Trap LPT is also under construction. In this symposium, the principle of the SHANS, the status of RFQ1L and LPT and some primary test results will be reported.

RFQ冷却聚束器RFQ1L的研制

SHANS (Spectrometer of Heavy Atoms and Nuclear Structure，重原子和核结构研究谱议)正在建设中，它不但可以直接鉴别离子的电荷数Z和质量数A，而且还将在核结构和核衰变的精细研究方面发挥重要作用。RFQ冷却聚束器RFQ1L和彭宁离子阱LPT是其中的两个重要组成部分。 RFQ冷却聚束器RFQ1L的主要目的是收集经过充气反冲谱议分离后的反应产物，然后经过冷却、聚束，使原来品质很差的束流转化为能量单一、发射度小、束斑很小的高品质束流。现在已经顺利完成了模拟、设计、机械加工和机械安装等工作，其中机械安装部分是本论文的主要工作之一。经过近半年的时间，我们克服了种种困难，高质量地完成了RFQ1L的机械安装工作。各种测量综合显示：各部件间的位置精度达到了±0.5 mm；真空系统的真空度达到了1.7×10-4 Pa，系统压升率为(0.04±0.02) Pa/h；各电极间的绝缘效果和导电效果良好。彭宁离子阱LPT的主要目的是直接高精度测量原子核的质量。质量是原子核的一个最基本属性，对检验和拓广现有核理论、研究核天体物理中的核反应过程和基本常数具有非常重要的作用。控制系统在LPT中起着至关重要的作用。控制系统的设计和实现也是本论文的另一个主要工作。本论文详细论述了LPT的控制系统LPTCtrlSys的基本要求、硬件和软件布局情况

超重谱仪中冷却聚束器RFQ1L的模拟研究

对超重核和超重元素越来越多的探索和研究，以及对远离β稳定线奇异核的精细研究，都迫切地需要低能量、高品质的放射性束流。然而，由原子核反应产生的放射性束流普遍具有能量分散大、发射度大以及束流斑点大的缺点，因此，对放射性次级束流进行进一步的操控成为深入研究的必需条件。充有缓冲气体的RFQ冷却聚束器是适合这项任务的最佳选择。它不但可以高速度、高效率地提高束流的品质，而且适用于所有的核素。这项技术在上世纪末蓬勃地发展起来，现在已经成为世界各主要实验室进行放射性次级束流操控的必备实验装置。在中国科学院近代物理研究所，一台正在研制的专用于研究长寿命核素的超重核研究谱仪中就使用了RFQ冷却聚束器来冷却、约束和储存离子。论文首先简单介绍了近代物理研究所超重谱仪的情况和国际上RFQ冷却聚束器的研究情况，其次阐述了RFQ冷却聚束器相关原理，然后重点论述了用SIMION程序进行模拟的方法和对RFQ1L冷却段的模拟情况，并对模拟结果进行了讨论，接着，讨论了计算机无法模拟的一些因素，重点讨论了气体击穿问题，最后，对本论文的工作进行了总结，并对下一步工作进行了展望望。对RFQ1L冷却段的模拟和气体击穿问题是本论文的两个重点。冷却段的模拟是以为例进行的。通过改变缓冲气体压强、入射离子能量以及轴向电场梯度，得到了离子在RFQ冷却聚束器中不同的运动情况，得到了一些有意义的结论，有助于设备的设计和工作点的选择。另外，RFQ冷却聚束器的工作区域，正好位于缓冲气体最容易被击穿的范围，再加上射频的影响，因此气体击穿问题成为制约工作点选择的一个非常重要的因素。本文对此也作了详细的讨论

内蒙古岱海DH99a岩芯沉积物碳含量变化与湖区全新世气候变迁

Daihai Lake, a graben-type closed lake, lies ca. 10 km east of Liangcheng County, Inner Mongolia, north-central China. For its location at the transition of semi-humid and semi-arid areas, and in the north edge of the East Asian monsoon, the lake is sensitive to changes in climate and environment. Based on analyses of total inorganic carbon (TIC), total organic carbon (TOC) and the ratio of total organic carbon to total nitrogen (C/N ratio) of DH99a core sediments recovered in the central part of Daihai Lake, the data suggest Holocene climatic history of the lake region is reconstructed. In this paper, the TIC and TOC contents of the lake sediments are closely related to climate changes. 1) Changes in TIC content of the lake sediments is closely related to climate, which directly reflect changes of temperature in the lake region, i.e., higher TIC content is linked with warmer temperature and stronger evaporation; 2) Changes in TOC and C/N ratio reflect the regional precipitation, i.e., relatively higher TOC content and C/N ratio indicate higher rainfall which results in stronger river flow and more organic matter entering into the lake. Data of the TIC content, TOC content and C/N ratio of DH99a core sediments suggest that climatic history of the Daihai Lake region is characterized by 4 stages. During the interval of ca. 11200-7500 a BP, higher TIC content, relatively lower TOC content and C/N ratio value indicate a warmer and slight dry condition over the lake area. From ca. 7500 to 4500 a BP, high values of TIC content, with an increase in TOC content and C/N ratio suggest the climate was warm and humid. Changes of TIC content, TOC content show that both temperature and precipitation displayed obvious fluctuations during the period, i.e., slightly cool and humid ca. 7500-6700 a BP, warm and moist ca. 6700-5300a BP, mild and comparatively humid ca. 5300-4500a BP. Between ca. 4500 and 2900 a BP, TIC content and TOC content decreased gradually while fluctuating, C/N ratio displayed a decreasing trend. These data imply that the climate generally became cooler and drier than the preceding period. The lowest values of TIC content, TOC content and C/N ratio during the interval of ca. 2900-0 a BP, demonstrate that the climate was severe, and became cool and dry. However the relative higher values of TIC content, TOC content and C/N ratio between ca. 1700 and 1300 a BP may denote an increase both in temperature and in precipitation. Data of TIC content, TOC content and C/N ratio in Daihai DH99a core sediments indicate that the warm period was asynchronous with the humid time, the warm interval began in ca. 11200 a BP, and ended in ca. 2900 a BP. The humid period was ca. 7500-2900 a BP. During ca. 7500^500 a BP, the climate was warm and humid, which was the climatic optimum of the Holocene Epoch in the Daihai Lake region. Data of TIC content, TOC content and C/N ratio in Daihai DH99a core sediments imply that the Holocene climate was unstable, the fluctuating events happened occasionally. Such as the cold and dry climate in ca. 4400-4200a BP, the warm and humid climatic condition in the period between ca.1700 and 1300a BP.

突出电极对四杆型RFQ腔体并联阻抗及场平整性的影响；Influence of projecting electrodes on shunt impedance and flatness of 4-rod radiofrequency quadrupole cavity

中国科学院近代物理研究所正在进行等离子体直接注入方案的研究,以便为重离子物理研究提供稳定可靠的高流强束流。由于工作频率较低,用于等离子体直接注入方案的RFQ腔体采用了适合于低频的四杆型结构。在完成束流动力学设计的前提下,研究了RFQ腔体支撑臂的各参数对并联阻抗的影响。由于突出电极之间存在着一定大小的电容,会对腔体的性能产生影响,为使腔体达到最优化的设计,进行了突出电极对并联阻抗及场平整性的影响的研究,并给出了突出电极的取值范围。

Study on shunt impedance and voltage distribution of 4-rod RFQ cavity

A high current RFQ (radio frequency quadrupole) is being studied at the Institute of Modern Physics, CAS for the direct plasma injection scheme. Shunt impedance is air important parameter when designing a 4-rod RFQ cavity, it reflects the RF efficiency of the cavity, and has a direct influence on the cost of the structure. Voltage distribution of a RFQ cavity has an effect on beam transmission, and particles would be lost if the actual voltage distribution is not as what, it should be. The influence of cell length, stern thickness and height on Shunt impedance and voltage distribution have been studied, in particular the effect of projecting electrodes has been investigated in detail.

Molecular phylogeography and population structure of a mid-elevation montane frog Leptobrachium ailaonicum in a fragmented habitat of southwest China

Leptobrachium ailaonicum is a vulnerable anuran restricted to a patchy distribution associated with small mountain streams surrounded by forested slopes at mid-elevations (approximately 2000-2600 m) in the subtropical Mount Wuliang and Mount Ailao ranges in southwest China (Yunnan Province) and northern Vietnam. Given high habitat specificity and lack of suitable habitat in lower elevations between these ranges, we hypothesized limited gene flow between populations throughout its range. We used two mitochondrial genes to construct a phylogeographic pattern within this species in order to test our hypothesis. We also examined whether this phylogeographic pattern is a response to past geological events and/or climatic oscillations. A total of 1989 base pairs were obtained from 81 individuals of nine populations yielding 51 unique haplotypes. Both Bayesian and maximum parsimony phylogenetic analyses revealed four deeply divergent and reciprocally monophyletic mtDNA lineages that approximately correspond to four geographical regions separated by deep river valleys. These results suggest a long history of allopatric separation by vicariance. The distinct geographic distributions of four major clades and the estimated divergence time suggest spatial and temporal separations that coincide with climatic and paleogeographic changes following the orogeny and uplift of Mount Ailao during the late Miocene to mid Pliocene in southwest China. At the southern distribution, the presence of two sympatric yet differentiated clades in two areas are interpreted as a result of secondary contact between previously allopatric populations during cooler Pleistocene glacial cycles. Analysis of molecular variance indicates that most of the observed genetic variation occurs among the four regions implying long-term interruption of maternal gene flow, suggesting that L ailaonicum may represent more than one distinct species and should at least be separated into four management units corresponding to these four geographic lineages for conservation. (C) 2009 Elsevier Inc. All rights reserved.

Modeling study to compare the flow and heat transfer characteristics of low-power hydrogen, nitrogen and argon arc-heated thrusters

A modelling study is performed to compare the plasma °ow and heat transfer char- acteristics of low-power arc-heated thrusters (arcjets) for three di®erent propellants: hydrogen, nitrogen and argon. The all-speed SIMPLE algorithm is employed to solve the governing equa- tions, which take into account the e®ects of compressibility, Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. The temperature, veloc- ity and Mach number distributions calculated within the thruster nozzle obtained with di®erent propellant gases are compared for the same thruster structure, dimensions, inlet-gas stagnant pressure and arc currents. The temperature distributions in the solid region of the anode-nozzle wall are also given. It is found that the °ow and energy conversion processes in the thruster nozzle show many similar features for all three propellants. For example, the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appear- ing near the cathode tip; the °ow transition from the subsonic to supersonic regime occurs within the constrictor region; the highest axial velocity appears inside the nozzle; and most of the input propellant °ows towards the thruster exit through the cooler gas region near the anode-nozzle wall. However, since the properties of hydrogen, nitrogen and argon, especially their molecular weights, speci¯c enthalpies and thermal conductivities, are di®erent, there are appreciable di®er- ences in arcjet performance. For example, compared to the other two propellants, the hydrogen arcjet thruster shows a higher plasma temperature in the arc region, and higher axial velocity but lower temperature at the thruster exit. Correspondingly, the hydrogen arcjet thruster has the highest speci¯c impulse and arc voltage for the same inlet stagnant pressure and arc current. The predictions of the modelling are compared favourably with available experimental results.

HIRFL-CSR commissioning in 2006 and 2007

HIRFL-CSR, a new heavy ion cooler-storage-ring system at IMP, had been in commissioning since the beginning of 2006. In the two years of 2006 and 2007 the CSR commissioning was finished, including the stripping injection (STI), electron-cooling with hollow electron beam, C-beam stacking with the combination of STI and e-cooling, the wide energy-range synchrotron ramping from 7 MeV/u to 1000 MeV/u by changing the RF harmonic-number at mid-energy, the multiple multi-turn injection (MMI), the beam accumulation with MMI and e-cooling for heavy-ion beams of Ar, Kr and Xe, the fast extraction from CSRm and single-turn injection to CSRe, beam stacking in CSRe and the RIBs mass-spectrometer test with the isochronous mode in CSRe by using the time-of-flight method.