Commissioning of electron cooling in CSRe

The 400 MeV/u 12C6＋ ion beam was successfully cooled by the intensive electron beam near 1 A in CSRe.The momentum cooling time was estimated near 15 s.The cooling force was measured in the cases of difierent electron beam profiles,and the difierent angles between the ion beam and electron beam.The lifetime of the ion beam in CSRe was over 80 h.The dispersion in the cooling section was confirmed as positive close to zero.The beam sizes before cooling and after cooling were measured by the moving screen.The beam diameter after cooling was about 1 mm.The bunch length was measured with the help of the signals from the beam position monitor.The difiusion was studied in the absence of the electron beam.     

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.     

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.     

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.     

Longitudinal Schottky spectra of a bunched Ne10+ ion beam at the CSRe

The longitudinal Schottky spectra of a radio-frequency (RF) bunched and electron cooled ²²Ne¹⁰⁺ ion beam at 70 MeV/u have been studied by a newly installed resonant Schottky pick-up at the experimental cooler storage ring (CSRe), at IMP. For an RF-bunched ion beam, a longitudinal momentum spread of Δp/p=1.6×10^-5 has been reached with less than 10⁷ stored ions. The reduction of momentum spread compared with a coasting ion beam was observed from Schottky noise signal of the bunched ion beam. In order to prepare the future laser cooling experiment at the CSRe, the RF-bunching power was modulated at 25^th, 50^th and 75^th harmonic of the revolution frequency, effective bunching amplitudes were extracted from the Schottky spectrum analysis. Applications of Schottky noise for measuring beam lifetime with ultra-low intensity of ion beams are presented, and it is relevant to upcoming experiments on laser cooling of relativistic heavy ion beams and nuclear physics at the CSRe.     

HIAF-SRing的等时性模式光学设计

高精度环形谱仪SRing作为HIAF装置的核心之一,是获取高品质放射性次级束,并将束流用于加速器技术研究、原子物理及核物理实验的关键设备。SRing有三种运行模式:等时性模式、正常模式与内靶模式。等时性模式下,SRing运行在特殊线性光学设置下,可以精确测量寿命低至几十微秒的原子核的质量。介绍SRing等时性模式的线性光学及高阶项校正的设计方案。在使用程序GICOSY进行等时性高阶项校正数值计算后,将得到的光学传输矩阵输入到程序MOCADI进行粒子跟踪模拟。以γ_t=1.43的等时性模式为例,SRing的动量接收度为±0.20%,粒子跟踪结果显示,在仅满足一阶等时性条件时SRing的质量分辨能力R=1.6×104。在保证动量接收度不变的前提下,考虑了等时性高阶项校正后SRing的质量分辨能力提高到R=1.2×106,达到设计要求。The Spectrometer Ring, as the most important experiment terminal of the High Intensity heavy-ion Accelerator Facility (HIAF) project, is a key device to obtain high-quality radioactive ion beams (RIBs) for atomic physics, nuclear physics experiments and accelerator technology researches. Three operation modes including the isochronous mode, the normal mode and the internal target mode, have been designed for the SRing. In the isochronous mode, the SRing operates under a special ion optics and could be used for precision mass measurement of short-lived nuclei with half-life shorter than several tens of microseconds. This study aims to design the ion optics for the isochronous mode and improve the mass resolving power of the SRing with higher-order ion-optical correction scheme for isochronism while preserve a large momentum acceptance of SRing. The ion optics and the higher-order correction for the isochronous mode are calculated with the code MAD-X and GICOSY respectively. Three ion optics with γ_t=1.43, 1.67, 1.83 settings have been calculated. The code MCOADI which utilizes the matrixes generated by the code GICOSY is used for particles tracking to verify the correction results. For the ion-optical setting of γ_t=1.43 with a momentum acceptance of ±0.20%, the mass resolving power of the SRing could be improved from R=1.6×104 to R=1.2×106, after isochronous higher-order corrections.     

基于HIAF SRing的并束实验设计及研究

超重核的真空衰变对于验证量子电动力学至关重要,由于过去的固定靶实验中,核外电子干扰正负电子对的测量,国际上尚未观测到该现象。提出基于HIAF SRing的并束实验方案,通过238U92+在自由空间碰撞,排除了核外电子的影响。根据亮度理论,结合对交叉角度、Laslett频移和束束相互作用的分析,优化得到1.9×1024 cm-2s-1的峰值亮度,基本满足了实验需求。Vacuum decay phenomenon of superheavy nucleus is a problem of fundamental interest to verify quantum electrodynamics. As the shell electrons interfere the detection of electron-positron pairs in the fixed target experiments in the past, it's still not corroborated. A new merging experiment scheme is proposed in this paper. The interference of shell electrons is eliminated by collisions of 238U92+ in free space. According to the luminosity theory and the analyses of crossing angle, Laslett tune shift and beam-beam interaction, an optimized peak luminosity of 1.9×1024 cm -2·s -1 is achieved. It meets the requirements of merging experiment essentially.     

冷却储存环CSRm中螺线管场耦合效应研究

介绍了重离子冷却储存环中螺线管场对束流水平方向和垂直方向产生耦合的原理, 由耦合运动方程及耦合系数推导出螺线管场耦合的补偿方法. 结合兰州冷却环主环实际的单元结构,工作点选在束流稳定的差共振附近, 模拟计算了冷却环主环在电子冷却段没有螺线管、有螺线管和增加补偿螺线管三种情况下的束流发射度及此三种情况下冷却环主环的动力学孔径. 通过模拟计算可知螺线管的存在将引起束流的水平方向和垂直方向严重耦合, 由于耦合效应, 垂直方向的发射度将超出其接受度, 致使束流大量损失. 针对这种情况, 提出了在螺线管两端的合适位置增加一组补偿螺线管的校正方案. 模拟结果表明这种措施行之有效.     

Bunch compression study using the envelope model in CSRm

The feasibility of attaining a short-pulse-duration heavy ion beam with a nanosecond pulse length is studied in the main ring of the Heavy Ion Research Facility in Lanzhou (HIRFL). Such a heavy ion beam can be produced by non-adiabatic compression, and it is implemented by fast rotation in the longitudinal phase space. In this paper, the possible beam parameters during longitudinal bunch compression are studied by using the envelope model. The result shows that a shortest heavy ion bunch ²³⁸U²⁸⁺ of 29 ns with energy of 200 MeV/u can be obtained, which can satisfy high energy density physics research.     

放射性次级束流分离器真空系统的压力分布

放射性次级束流分离器是强流重离子加速器装置中,连接增强器和高精度环形谱仪的束流输运线,用于传输重离子束流以及放射性次级束流。为了满足束流传输的要求,并维持相连增强器和高精度环形谱仪的极高真空,放射性次级束流分离器真空系统的平均压强应低于5×10-7 Pa。因此,需要验证真空系统设计方案的可行性,以及设计方案能否满足要求的压强范围。通过现有的同步储存环CSRm中的真空计监测数据以及软件BOLIDE的模拟结果对比,对真空压力计算软件VAKTRAK的使用方法和计算结果进行验证;采用VAKTRAK模拟计算不同真空参数下（流导、出气率以及泵速）放射性次级束流分离器真空系统的压力分布。根据计算结果,放射性次级束流分离器真空系统的平均压强可以达到1.79×10-7 Pa （H₂）,满足物理实验和工程设计的要求。通过模拟计算结果,放射性次级束流分离器真空系统的设计方案的可行性得到验证,系统设计的真空度满足要求。HIAF Fragment Separator(HFRS) is connected with Booster Ring(BRing) and Spectrometer Ring (SRing) in the HIAF and used to transfer the ion beams and radioactive secondary beams. To satisfy the requirements of beam transmission and maintain the extremely high vacuum of BRing and SRing, the average pressure of HFRS vacuum system should be lower than 5×10-7 Pa. Therefore, the feasibility of the design scheme and whether the design scheme would fulfill the required vacuum range or not should be verified. Based on the measured data on the current sychrontron CSRm and the simulation results of BOLIDE, the calculation results of VAKTRAK are verified and then VAKTRAK is used to calculate the pressure profiles of different parameters(such as the conductance, out-gassing and pumping speed) for HFRS. According to the calculation results, the average pressure of HFRS vacuum system could be 1.79×10-7(H₂) which achieves the required pressure for physics experiments and engineering design. According the calculation results of this paper, the feasibility of the designed HFRS vacuum system has been verified and the design of system satisfies the vacuum requirements.