Laser pumping of ions in a cooler buncher

Optical experiments at the IGISOL isotope separator facility, Jyväskylä, have for many years benefited from the introduction of an ion beam cooler. The device, a gas-filled RF quadrupole, reduces the emittance and longitudinal energy spread of the ion beam. Very recently, use has been made of the axial confinement of slowly travelling ions at the end of the cooler to redistribute the electronic populations through efficient laser excitation. Such a technique has proved beneficial to laser spectroscopic measurements and is a precursor to using the method to polarize the ion beam.     

Time Characteristics of the Ion Beam Cooler-Buncher at JYFL

A beam cooler for low-energy ion beams was constructed to improve the ion optical properties of radioactive ion beams produced at the IGISOL facility in Jyväskylä. The beam cooler is a buffer gas filled RF-quadrupole. The delay properties and the possibility to accumulate a continuous IGISOL beam and release it in short bunches is discussed.     

Status of the LASER-IGISOL collaboration at the University of Jyväskylä

Recent laser spectroscopy studies at the IGISOL facility, University of Jyväskylä have focussed on the shape transition at N?=?60. A new technique of optical pumping in the ion beam cooler has given unique access to the radioactive isotopes of niobium and yttrium. Further spectroscopy from metastable states allowed nuclear moments and charge radii to be extracted for isotopes in the chains of Mo and Nb, thus exploring the extent of nuclear deformation across the entire Z?=?36–42 region.     

Probing a cooled beam of decelerated highly-charged heavy ions extracted out of the ESR by a channeling experiment

A cooled beam of decelerated highly-charged heavy ions is slowly extracted out of the cooler and storage ring ESR, by combining the deceleration technique and the charge exchange extraction mode. The quality of the external ion beam is tested by a channeling experiment. Bare Au⁷⁹⁺ ions are injected into the ESR at an energy of 360 MeV/u, decelerated to 53 MeV/u, and finally cooled strongly in the electron cooler. By breeding of neighboring charge state ions via radiative recombination in the electron cooler H-like ions are produced. The H-like ion fraction is extracted out of the storage ring. This extracted Au⁷⁸⁺ ion beam is probed by a channeling experiment measuring the extinction rate of the projectile Kα X-ray yield around the [110] axis of a thin silicon crystal. This revised version was published online in August 2006 with corrections to the Cover Date.     

Commissioning of electron cooling in CSRm

A new generation electron cooler has started operation in the heavy ion synchrotron CSRm which is used to increase the intensity of heavy ions. Transverse cooling of the ion beam after horizontal multi-turn injection allows beam accumulation at the injection energy. After optimization of the accumulation process an intensity increase in a synchrotron pulse by more than one order of magnitude has been achieved. In given accumulation time interval of 10 seconds, 108 particles have been accumulated and accelerated to the final energy. The momentum spread after accumulation and acceleration in the 10-4 range has been demonstrated in six species of ion beams. Primary measurements of accumulation process varying with electron energy, electron beam current, electron beam profile, expansion factor and injection interval have been performed. The lifetimes of ion beams in the presence of electron beams were roughly measured with the help of DCCT signal.     

Commissioning of electron cooling in CSRm

A new generation electron cooler has started operation in the heavy ion synchrotron CSRm which is used to increase the intensity of heavy ions. Transverse cooling of the ion beam after horizontal multi-turn injection allows beam accumulation at the injection energy. After optimization of the accumulation process an intensity increase in a synchrotron pulse by more than one order of magnitude has been achieved. In given accumulation time interval of 10 seconds, 10⁸ particles have been accumulated and accelerated to the final energy. The momentum spread after accumulation and acceleration in the 10^－4 range has been demonstrated in six species of ion beams. Primary measurements of accumulation process varying with electron energy, electron beam current, electron beam profile, expansion factor and injection interval have been performed. The lifetimes of ion beams in the presence of electron beams were roughly measured with the help of DCCT signal.     

Resonance ionization spectroscopy of bismuth at the IGISOL facility

A programme of research has commenced at the IGISOL facility, Jyväskylä, combining the technique of resonance ionization spectroscopy with the development of the highly selective laser ion source trap (LIST). The first element of interest is bismuth, which contains three isomers of multi-quasiparticle states in near-spherical nuclei, namely ²⁰⁷Bi (21/2⁺, 182 μs), ²⁰⁴Bi (10^?, 13 ms) and ²⁰⁴Bi (17⁺, 1.07 ms). A measurement of the optical isomer shift provides a direct comparison of the mean?square charge radii between the isomer and the nuclear ground state. Due to the short isomer lifetimes the spectroscopy will be done either within the ion guide or in a sextupole ion beam guide (SPIG), located after the ion guide and used in the development of the LIST. A mixed dye-Ti:Sapphire laser ionization scheme has been successfully tested for bismuth and first off-line results have been obtained.     

HIRFL-CSR实验环中束流损失机制及寿命研究

分析了在储存环中回旋的离子束与残余气体分子、 内靶和冷却电子束相互作用时的损失机制及相应的束流寿命, 针对兰州重离子加速器冷却储存环实验环内靶模式, 计算了50—500 MeV/u 12C6+, 36Ar18+, 132Xe54+和 238U92+等束流在各种损失机制影响下所对应的束流寿命和总的束流寿命。 结果表明: 影响束流寿命的主要因素是与内靶分子（原子）之间的电荷交换及与冷却电子束之间的辐射复合; 对于重离子束 132Xe54+和 238U92+, 与冷却电子束之间的辐射复合是影响其储存寿命的主要因素。The loss mechanism and lifetime of ion beams in collisions with residual gas, internal target and electrons in e cooler in heavy ion cooler storage rings were studied. The partial beam lifetimes resulting from various loss mechanisms and the total beam lifetimes of 50—500 MeV/u12C6+, 36Ar18+, 132Xe54+ and 238U92+ stored in the experimental ring of the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou (HIRFL CSR) were calculated. The calculations indicate that the charge exchange process between ion beams and the internal target, as well as the radiative recombination process with the electrons in e cooler restrict the beam lifetime considerably. For heavy ion beams such as 132Xe54+ and 238U92+, the radiative recombination is the dominant loss mechanism     

Development Towards a Laser Ion Source Trap for the Production of Exotic Species

A new type of resonance ionization laser ion source (RILIS) is presently being developed and tested at the off-line mass separator at Mainz University for future use at on-line exotic rare isotopes production facilities. For highest isobaric selectivity, this RILIS approach decouples the evaporation and ionization process. A further advantage is the generation of full temporal control of the resulting high quality ion beam. These facts are realized by a combination of atomizer – ion repeller – ion cooler and trap, which is operated together with a state-of-the-art, all solid state laser system. The principle and performance of this laser ion source trap (LIST) system are discussed applying simulation studies for the repeller-trap combination and first measurements for characterization.     

Positive ion extraction from plasma source and its application in fusion research

Neutral Beam Injection (NBI) is well established technique for heating tokamak plasma and is used in all fusion research programs [1–2]. In our Steady state Superconducting Tokamak (SST) machine [3], neutral hydrogen beam power of 0.5 MW at 30 kV is required to raise plasma ion temperature of ∼1 keV. Future upgrade of the SST will require 1.7 MW of H^o at 55 kV. To fulfill this requirement, an ion extractor system (heart of any NBI system) has been designed to extract 35A H⁺ beam current at 30 kV and of 90 A at 55 kV respectively [4]. In this paper, we have described the physics and ion beam optics study for an ion extraction system suitable for above mentioned long dynamic range of acceleration voltage. The ion beam optics simulation result is used as an input to the engineering design. After fabrication, its performance test has been done. The experimental results are in very good agreement with beam optics simulation.     

LIST developments at IGISOL

The ion guide technique was developed in Jyv?skyl? during the early 1980's. In the ion guide the reaction recoil products are stopped and thermalized in high purity helium gas where they remain ionic due to high ionization potential of helium atoms. Different designs of ion guide exist for light-ion induced fusion reactions, for heavy-ion induced fusion and for proton induced fission. Although the IGISOL method is fast and universal it is chemically unselective and in many cases relatively inefficient. In order to address these deficiencies in the technique, a new laser ion source project, FURIOS (Fast Universal Resonant laser Ion Source), commenced in 2004. In addition, resonance ionization spectroscopy has been tested off – line within a sextupole ion beam guide.     

Plans for atomic physics with highly-charged ions at Lanzhou

The upgraded radioactive ion beam line of Lanzhou and the project of the cooler storage ring of Lanzhou are presented in this paper. The plans for atomic physics with highly charged ions at the cooler storage ring are discussed briefly, including precision spectroscopy of highly charged ions, free- and laser-induced electron–ion recombination, test of special relativity, hyperfine structure of radioactive ions, lifetime measurements, and internal target experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

重离子治癌终端的束流强度及剂量监测系统

 为实现重离子肿瘤治疗临床实验中对照射束流状态的实时监测,研制了束流强度及剂量监测系统,包括积分电离室、后续电流频率转换电路及LabVIEW数据获取处理三部分。利用闪烁体探测器和标准剂量计测试了系统的线性响应和得到剂量的准确性,结果表明：系统在束流临床照射流强范围内的线性响应好于90%,其实时反馈的临床照射剂量偏差小于5%。同时束流强度及剂量监测系统与安全控制系统相结合,保证束流照射状态满足临床照射的安全要求。     

RFQ冷却聚束器研究简介

详细论述了RFQ冷却聚束器相关的基本原理,简单介绍了国际上此方面的研究和我们的工作。The radiofrequency quadrupole （RFQ） cooler and buncher has been developed in many laboratories to improve the secondary radioactive ion beam quality. In this paper, the principles of the RFQ constraint, buffer gas cooling, axial electric field and Paul trap are discussed in detail. The studies around the world and our work are also briefly introduced.     

Side-effects of the space charge field introduced by a hollow electron beam in the electron cooler of CSRm

An electron cooler is used to improve the quality of the ion beam in a synchrotron;however it also introduces a nonlinear electromagnetic field to the accelerator,which causes tune shift,tune spread and may drive resonances leading to ion beam loss.In this paper the tune shift and the tune spread caused by the nonlinear electromagnetic field of a hollow electron beam is investigated,and the resonance driving terms of the nonlinear electromagnetic field are analysed.The differences are presented compared with a solid electron beam.Calculations are performed for ~(238)U~(32+) ion of energy 1.272 MeV stored in the main Cooler Storage Ring(CSRm) at the Institute of Modern Physics,Lanzhou.It is found that in this situation the nonlinear field caused by the hollow electron beam does not lead to serious resonances.     

HIRFL-CSR电子冷却束流位置测量系统

高效率的电子冷却过程, 要求电子束与离子束位置平行且重叠。 为了同时测量电子束与离子束的位置, 在HIRFL CSR电子冷却装置上研发了以容性圆筒形极板为感应电极的束流位置探测系统。 系统测量束流通过探针时产生的脉冲感应信号, 并进行傅里叶变换得到频谱信号, 分析4个不同电极上频谱信号强度获取束流的位置信息。 测量结果表明, 该束流位置探测系统测量准确, 为定量研究储存环离子累积和电子冷却过程与两种束流相对位置及角度的依赖关系提供了条件。 The efficient electron cooling requires that the ion beam and electron beam are parallel and overlapped. In order to measure the positions of ion beam and electron beam simultaneously, a beam position monitor system is developed for the HIRFL-CSR electron cooler device, which probe consists of four capacitive cylinder linear cut poles. One can get the both beam positions from the picking up signals of four poles by using Fourier transform(FFT) method. The measurement results show that the beam position monitor system is accurate. This system is suitable for investigating the relation between electron cooling processing and the angle of ion beam and electron beam.     

First principles study of nuclear quadrupole interactions in the molecular solid BF3 and the nature of binding between the molecules

The LPCTrap facility is coupled to the low-energy beam line LIRAT of the SPIRAL source at GANIL (France). The facility comprises an RFQ trap for beam preparation and a transparent Paul trap for in-trap decay studies. The system has been tested for several ion species. The Paul trap has been fully characterized for ⁶Li⁺ and ²³Na⁺ ions. This characterization together with GEANT4 simulations of the in-trap decay setup (Paul trap and detection system) has permitted to predict the effect of the size of the ion cloud on the decay study of ⁶He⁺.     

Collinear laser spectroscopy with reverse-extracted bunched beams at TRIUMF

Collinear laser spectroscopy with reverse-extracted cooled bunched beams was performed at TRIUMF with radioactive ion beams. Surface-ionized ^78,78mRb ions were injected into TITAN??s cooler-buncher, and reverse-extracted to the laser beam line. There they were neutralised and excited with a counter-propagating laser beam. The fluorescence signal from the D ₂ line was recorded with a photomultiplier tube. The cooler provided typically 50 ion bunches per second, with each bunch containing approximately 10⁵ ions, temporally distributed with a 1.6 ??s width. A hardware gate was set on the signal, suppressing the background by four orders of magnitude.     

超重核研究谱仪的RFQ冷却聚束器RFQ1L

介绍了超重核研究谱仪中RFQ冷却聚束器RFQ1L的结构和运用SIMION程序对离子的冷却、聚束、引出和撇气过程的模拟情况。 模拟显示: 通过仔细选择工作点就完全可以把经过充气反冲质量分离器分离后的低品质束流转化为斑点小、发射度小和能量单一的高品质束流, 为紧接其后的磁铁和激光高效率分析提供条件。The structure and the simulation results about the cooling,bunching,extraction and skimming of the RFQ cooler and buncher RFQ1L, which is an important part of the being built super heavy nuclide research spectrometer, have been introduced. It shows that, by careful choice of its working point, we can obtain an ion beam with small beam spot, small emittance and mono energy, which can satisfy the requirements of the successive analyses by dipole and laser with high efficiencies.