ADS注入器II的5 MeV高能传输线的设计与搭建

ADS先导专项的注入器Ⅱ计划在将质子束通过一个Cryomodule加速到5 MeV后,进行10 mA连续束流的调试,以验证ADS低能段的强流超导直线加速器技术。为了将50 kW的束流功率沉积到束流垃圾站,需要搭建一条高能束流传输线,从超导段开始传输束流。采用两套三组合四极透镜控制束流包络及垃圾站的束流尺寸,利用诊断真空室进行水平和垂直发射度的测量。为避免束流产生的真空管道损伤,该传输线必须确保束流无损失地传输到垃圾站。A CW 10 mA,5 MeV beam commissioning of CADS Injector Ⅱ is planed recently to test the high power superconduction linac techniques.To transport 50 kW beam from linac to the beam dump,a high energy beam line (HEBT) line is designed and setup.Two Triplet are used to control the beam size along HEBT and at the beam dump.One diagnostics box is used for horizontal and vertical emittance measurement.To avoid damages to the vacuum pipe,beam should be transported to the beam dump without losses.The details of the HEBT design will be described in the paper.     

SSC-LINAC重离子RFQ动力学模拟与研究

采用多粒子跟踪程序BEAMPATH 对SSC-LINAC 重离子RFQ 直线加速器进行动力学模拟,分别对RFQ 的接受度、高频特性、束流稳定性、空间电荷效应等进行了分析。该RFQ具有很大的纵向接受度,有利于束流在RFQ中的传输;高频特性研究表明,翼间电压设定在理论值以上时,该RFQ都能保持较好的束流特性;束流稳定性分析结果表明,该RFQ具有很大的束流失配容忍度;空间电荷效应研究表明,当束流强度低于0.5 mA时,束流传输不受影响。综合研究结果表明,53.667 MHz重离子RFQ具有较好的动力学特性,满足SSC-LINAC直线加速器的设计要求。The RFQ beam dynamics of a heavy ion linac was investigated in this paper and the BEAMPATH code was employed in this study. The main research was focused on the beam performances depending on longitudinal acceptance, RF properties, beam instability and space charge effect. The RFQ has large longitudinal acceptance in design, which brings the beam performances well. In the RF parameter study, the beam can keep good transmission in the acceleration even the vane voltage is larger than the theoretical value. It is also shown that the RFQ has a large robustness for the mismatch of the input beam by the analysis of the beam instability.Furthermore, the beam evolution is independent on the space charge effect when the beam current is less than 0.5 emA. The preliminary analysis of the beam dynamics shows that the 53.667 MHz heavy ion RFQ has a promising performance, which meets the requirements of SSC-LINAC.     

热屏位置对直拉硅单晶V/G、点缺陷和热应力影响的模拟

为了研究热屏位置对φ200 mm直拉硅单晶V/G、原生点缺陷浓度场以及热应力场的影响,使用CGSim有限元模拟软件进行了系统模拟.结果表明:热屏位置对硅单晶的V/G和原生点缺陷浓度的径向分布规律没有影响;较热屏至晶体侧表面距离相比,其底端至熔体表面距离的影响更大,即随着它的增加,V/G值沿径向普遍增大且由内向外变化程度增强,晶体心部高浓度空位区扩大,最大热应力减小.合理控制热屏底端至熔体表面的距离可有效改善晶体质量.     

全剥离离子94mRu44+的衰变研究

在兰州重离子加速器冷却储存环（HIRFL-CSR）上,用等时性质量谱仪首次研究了百微秒量级全剥离离子94mRu44+的衰变。94mRu44+由初级束流112Sn轰击Be靶产生,经过放射性束流线RIBLL2的筛选后注入到等时性设置的实验环CSRe中,并利用安装在实验环中的飞行时间探测器测量离子在CSRe中的循环周期。94mRu44+退激引起的质量改变会带来其循环周期的变化,由此直接观测到了94mRu44+退激到基态的过程。确定了本次实验中衰变事例探测的灵敏区间,并讨论了衰变发生时刻的测量精度。同时,测量了短寿命核素94mRu44+的质量,其半衰期约为100 μs,这是目前储存环质量谱仪测量的最短寿命核素的质量。The decay of the fully stripped ion 94mRu44+ in the order of one hundred microseconds has been studied for the first time by using the Isochronous Mass Spectrometry (IMS) at the HIRFL-CSR facility in Lanzhou. 94mRu44+ was produced via projectile fragmentation of a 112Sn primary beam bombarding on a 9Be production target. After the in-flight separation with RIBLL2, the ions were injected into the experimental ring (CSRe) and then stored there. The revolution times of the stored ions were measured by a Time-of-Flight (TOF) detector. Due to the mass change of a 94mRu44+ ion caused by its de-excitation to the ground state, hence the revolution time change, the decay process of 94mRu44+ could be directly observed in the CSRe. The sensitive window for detection of the decay events and the measurement precision of the decay time have been determined in this work. At the same time, we measured the mass of short-lived 94mRu44+ with the half-life about one hundred microseconds, which is the shortest among nuclides that have been studied by using storage-ring mass-spectrometry.     

固态氚增殖包层中球床堆积性能研究

基于球床堆积实验和离散元数值模拟对包层中球床的堆积性能做了初步研究。圆柱形一元(单尺寸颗粒)球床的堆积性能的结果显示随着球床直径与颗粒直径比的增大,球床的平均堆积因子逐渐增高,实验与模拟结果一致;采用二元颗粒(双尺寸颗粒)、提高颗粒粒度比可以显著提高球床的堆积因子,二元球床的堆积因子随着大颗粒体积分数的增加先增加后减小,在大颗粒体积分数约为60%~80%时达到最大。优化了二元球床的填充工艺,最终二元球床的堆积因子基本达到0.8,但球床的均匀性欠佳。     

硅酸锂球床等效导热率研究

基于计算流体力学(CFD)方法,结合国际热核实验反应堆(ITER)中实际使用的设计参数,对硅酸锂球床的传热特性进行了流固耦合传热分析,给出了多种工况下的热工水力结果。同时将用CFD得到的球床区域等效导热系数与相关实验的结果进行了比较。     

CSR-LINAC IH-RFQ的高频电磁设计

中国科学院近代物理研究所在CSR-LINAC项目中设计了一台108.48 MHz的IH型RFQ直线加速器。该RFQ可以将质荷比为3~7的离子从4 keV/u加速到300 keV/u。在完成束流动力学设计的基础上,主要针对RFQ腔体的高频电磁设计展开了研究,同时利用了电磁场仿真和束流动力学模拟来研究腔体的四极场不平整度和二极场及其动力学影响。未经调谐的情况下,腔体的谐振频率为108.15 MHz,腔体空载品质因子Q₀为5 910,腔体功耗为123 kW。通过在支撑板两端增加底切的设计,将腔体的四极场不平整度由-21%~ 12%优化至±2.5%,满足了束流动力学要求。腔体的二极场为-3%~ -2.2%,使得束流在垂直方向小幅振荡,RFQ的垂直方向接受度减小5%。为了保证功率馈入时反射较小,将耦合器设置在临界耦合状态,耦合面积为940 mm2。为了补偿腔体的频率偏差和漂移,设计了调谐量分别为707和132 kHz的固定调谐器和可动调谐器。The 108.48 MHz IH type RFQ for CSR-LINAC project is under design at Institute of Modern Physics, Chinese Academy of Sciences. This RFQ can accelerate heavy ions with mass to charge ratio of 3~7 from 4 keV/u to 300 keV/u. According to the beam dynamics requirement, the RF structure design has been finished. The quadrupole field unflatness and dipole field of the cavity were studied by electromagnetic simulation and beam dynamics simulation. The frequency of the cavity without tuning is 108.15 MHz, the Q₀ of the cavity is 5910, and the RF power loss is 123 kW. The quadrupole field unflatness of ±2.5%,which was -21%~12% before optimizing, is achieved to meet dynamics requirement through the undercuts in cavity supporters. The dipole field of -3%~ -2.2% causes the oscillation of the beam center and acceptance reduction of 5%. The power coupler must be in critical coupling state with the coupling area of 940 mm2 for minimum reflection coefficient. The tuners, consist of coarse and fine tuners with frequency shift of 707 and 132 kHz respectively, is used for tuning of frequency deviation of the cavity.     

缺中子核素101In低位同核异能态的首次观测

在兰州重离子加速器冷却储存环（HIRFL-CSR）上,用初级束流112Sn35+轰击了靶厚约10 mm的Be靶,产生了101In的基态和低位同核异能态。这些实验产生的碎片每25 s经过放射性束流线RIBLL2的筛选后注入到实验环CSRe中,利用飞行时间探测器测量离子在CSRe中的回旋周期。在此次实验中,磁场晃动会导致离子在环内的循环周期发生改变,传统的离子鉴别方法难以完成大部分离子的鉴别。通过发展和运用单次注入离子鉴别这一新的离子鉴别方法,有效地消除了磁场晃动对于离子鉴别的影响,并清楚地将101In基态和低位同核异能态鉴别出来,从而首次在实验中观测到101In的低位同核异能态。实验得到的激发能与理论外推值在112 keV的误差范围内一致,其低位同核异能态的寿命大于200 μs。Isochronous mass spectrometry has been applied to 112Sn projectile fragments at the HIRFL-CSR facility in Lanzhou. To produce short-lived nuclei of interest, we used projectile fragmentation of 112Sn35+ primary beams in a~10 mm thick 9Be production target. The fragments were selected and analyzed by RIBLL2 and injected into the experimental storage ring(CSRe) every 25 s. To measure revolution times of stored ions,we used a Time-Of-Flight detector installed in CSRe. A new particle identification method was developed to distinguish ions on the measured revolution time spectrum for each injection. Based on this method, the shifts of the revolution time due to instable dipole magnet fields can be corrected and the ground and isomeric states of 101In have been well-resolved. The measured excitation energy is consistent with the theoretical value in the error range of 112 keV. The lifetime of the isomeric states of 101In is more than 200 μs.     

HIRFL-CSR complex

The construction and commissioning of HIRFL-CSR were finished in 2007. From 2000 to 2005 the subsystem and key devices of CSR were successfully fabricated, such as magnet, power supply, UHV system, e-cooler, electric-static deflector with the septum of 0.1 mm, and the fast-pulse kicker with the rise time of 150 ns. After that the CSR commissioning activities were performed in 2006 and 2007, including the accumulation of those heavy ions of C, Ar, Kr and Xe by the combination of stripping injection （STI） or multiple multi-turn injection （MMI） and e-cooling with a hollow e-beam, wide energy-range synchrotron ramping by changing the RF harmonic-number at mid-energy, the beam stacking in the experimental ring CSRe, the RIBs mass-measurement with the isochronous-mode in CSRe by using the time-of-flight method, and the ion beam slow-extraction from CSRm.     

悖论与分式方程

数学上有一个著名的“2 =1悖论” .通过证明得出 2 =1的结论 .具体过程如下 :证明　设ａ =ｂ ,则ａ2 =ａｂ .ａ2 -ｂ2 =ａｂ -ｂ2 .(ａ +ｂ) (ａ -ｂ) =ｂ(ａ -ｂ) ,ａ +ｂ =ｂ ,ｂ +ｂ =ｂ ,2ｂ =ｂ ,2 =1.这个看似天衣无缝的证明 ,其实并不严密 .第 4步 (ａ +ｂ) (ａ -ｂ) =ｂ(ａ -ｂ)到第 5步ａ +ｂ =ｂ ,是两边同时除以 (ａ -ｂ) ,但我们假设ａ =ｂ ,所以ａ -ｂ =0 ,因此我们是在两边同时除以 0 ,于是出现了悖论 .利用这个悖论可以很好地说明分式方程增根的问题 .为了明晰起见 ,将这几步重新书写于下 ,并添补上最关键的一步 .(ａ +ｂ) (…