26 Al beam production by a solid state laser ion source at TRIUMF

Many experiments carried out at radioactive beam facilities require the production of intense, isotopically clean and isobar free beams of a particular isotope. At TRIUMF the addition of a resonant ionization laser ion source (TRILIS) enables a multitude of new beams and therefore new experiments to be carried out. ²⁶Al was one of the first radioactive ion beams delivered to an experiment using TRILIS. This paper outlines the development of the ²⁶Al ion beam for nuclear astrophysics.      

Segmented linear radiofrequency quadrupole/laser ion source project at TRIUMF

Reactions such as ²⁵Al(p,γ)²⁶Si are the key to understand the production of ^26g Al and ^26m Al in our galaxy. Experimental results could provide important constraints on nova nucleosynthesis and modelling where ²⁶Al is believed to be produced. To achieve such measurements, high-intensity and high-purity radioactive beams are required. However, production targets at ISOL-type facilities such as ISAC at TRIUMF produce high-intensity alkali beams by surface ionization on hot transfer tubes hampering the measurement of isotopes of interest. To overcome this issue, an ion source combining a segmented linear radiofrequency quadrupole (RFQ) to a laser ion source is being built. Its main function is to suppress alkali impurities whilst allowing for fast-release of short-lived isotopes. The beam production method, the RFQ/laser ion source and the removal of alkali contaminants are discussed in this paper.     

Resonant Ionization Laser Ion Source Project at TRIUMF

Resonant laser excitation and ionisation is one of the most successful tools for the selective production of radioactive ion beams (RIB) at on-line mass separator facilities. TRIUMF plans to augment the current ion sources with a resonant ionisation laser ion source (RILIS), to use the high production yields from the target, as shown by the delivery of 3*10⁴/s ¹¹Li ions from a standard target ion source with surface ionisation. The development and installation of TRIUMF's RILIS (TRILIS) is necessary to provide beams of short lived isotopes that conventional ion sources could not produce in sufficient intensity and purity for nuclear-, and nuclear astrophysics- experiments. A laser system consisting of three tunable titanium–sapphire (TiSa) lasers with frequency doubling and tripling was employed to demonstrate first off-line resonance ionisation of Ga, and is being installed for first on-line test and a run on ⁶²Ga in December 2004.     

ECR ion source based low energy ion beam facility

Mass analyzed highly charged ion beams of energy ranging from a few keV to a few MeV plays an important role in various aspects of research in modern physics. In this paper a unique low energy ion beam facility (LEIBF) set up at Nuclear Science Centre (NSC) for providing low and medium energy multiply charged ion beams ranging from a few keV to a few MeV for research in materials sciences, atomic and molecular physics is described. One of the important features of this facility is the availability of relatively large currents of multiply charged positive ions from an electron cyclotron resonance (ECR) source placed entirely on a high voltage platform. All the electronic and vacuum systems related to the ECR source including 10 GHz ultra high frequency (UHF) transmitter, high voltage power supplies for extractor and Einzel lens are placed on a high voltage platform. All the equipments are controlled using a personal computer at ground potential through optical fibers for high voltage isolation. Some of the experimental facilities available are also described.     

离子束清洗在激光薄膜中的应用

介绍了在激光薄膜中End Hall型离子源离子束清洗的应用。通过实验验证了基片的二次污染和离子束的清洗效果,观测了离子束清洗前后基片的表面形貌变化。研究了用离子束清洗基片时对薄膜抗激光损伤阈值的作用。分析了用离子束清洗基片时其基片表面的性质,如清洁度、表面能、接触角、表面形貌的变化机理。指出了杂质微粒的去除和附着力的增加是如何使薄膜抗激光损伤阈值显著提高的。     

Conceptional design of the laser ion source based hadrontherapy facility

A laser ion source (LIS), which can provide a carbon beam with highly stripped state (C⁶⁺) and high intensity (several tens mA), would significantly change the overall design of the hadrontherapy facility. The proposed LIS based hadrontherapy facility has the advantages of short linac length, simple injection scheme, and small synchrotron size. With the experience from the DPIS and HITFiL projects that have been conducted in IMP, a conceptional design of the LIS based hadrontherapy facility will be presented, with special attention given to APF type IH DTL design and simulation.     

不同磁路电子回旋共振离子源引出实验

空间推进所用的电子回旋共振离子源(ECRIS)应具有体积小、效率高的特点. 本文研究的ECRIS使用永磁体环产生磁场, 有效减小了体积, 该离子源利用微波在磁场中加热电子, 电子与中性气体发生电离碰撞产生等离子体. 磁场在微波加热电子的过程中起关键作用, 同时影响离子源内等离子体的约束和输运. 通过比较四种磁路结构离子源的离子电流引出特性来研究磁场对10 cm ECRIS性能的影响. 实验发现: 在使用氩气的条件下, 特定结构的离子源可引出160 mA的离子电流, 最高推进剂利用率达60%, 最小放电损耗为120 W·A^-1; 所有离子源均存在多个工作状态, 工作状态在微波功率、气体流量、引出电压变化时会发生突变. 离子源发生状态突变时的微波功率、气体流量的大小与离子源内磁体的位置有关. 通过比较不同离子源的引出离子束流、放电损耗、气体利用率、工作稳定性的差异, 归纳了磁场结构对此种ECRIS引出特性的影响规律, 分析了其中的机理. 实验结果表明: 保持输入微波功率、气体流量、引出电压不变时, 增大共振区的范围、减小共振区到栅极的距离, 离子源能引出更大的离子电流; 减小共振区到微波功率入口、气体入口的距离能降低维持离子源高状态所需的最小微波功率和最小气体流量, 提高气体利用率, 但会导致放电损耗增大. 研究结果有助于深化对此类离子源工作过程的认识, 为其设计和性能优化提供参考.     

Tungsten ion source under double-pulse laser ablation system

New tungsten ion source is produced by using single and double-pulse laser ablation system. Combined collinear Nd:YAG laser beams(266+1064 nm) are optimized to focus on the sample in air. Optimization of the experimental parameters is achieved to enhance the signal-to-noise ratio of the emission spectra. The velocity distribution of the emitted plasma cloud is carefully measured. The influences of the potential difference between the bias electrodes, laser wavelength and intensity on the current signal are also studied. The results show that the increase in the tungsten ion velocity under the double-pulse lasers causes the output current signal to increase by about three folds. The electron density and temperature are calculated by using the Stark-broadened line profile of tungsten line and Boltzmann plot method of the upper energy levels, respectively. The signal intensity dependence of the tungsten ion angular distribution is also analyzed. The results indicate that the double-pulse laser ablation configuration is more potent technique for producing more metal ion source deposition, thin film formation, and activated plasma-facing component material.     

Charge state distribution analysis of AI and Pb ions from the laser ion source at IMP

A prototype laser ion source that could demonstrate the possibility of producing intense pulsed high charge state ion beams has been established with a commercial Nd：YAG laser （E =3 J, 1064 rim, ~ 10 ns） to produce laser plasma for the research of Laser Ion Source （LIS）. At the laser ion source test bench, high purity （99.998%） aluminum and lead targets have been tested for laser plasma experiment. An Electrostatic Ion Analyzer （EIA） and Electron Multiply Tube （EMT） detector were used to analyze the charge state and energy distribution of the ions produced by the laser ion source. The maximum charge states of A112＋ and Pb7＋ were achieved. The results will be presented and discussed in this paper.     

RF离子源引出特性的研究

为了使RF离子源具有良好的引出特性,测试了吸极几何参数、振荡器板压和引出电压对离子源聚焦度的影响,对实验结果进行了分析。在其它参数不变的情况下,吸极的外径D与内径d之比存在最佳值,增加D/d,有利于过聚焦的离子束恢复聚焦状态。吸极的长度为L,石英套管比吸极长l。当l/D增大时,聚焦度上升,引出束流下降。L/d之比减小时,聚焦度增大。当L/d小于4时,聚焦度增加趋势变缓。综合考虑聚焦度、引出束流和气压,D/d,l/D,L/d适宜的选择范围分别为1.6～2.1,0.7～1.1,4～7。增加振荡器功率会使离子束呈弱聚焦,而增加引出电压会使离子束呈过聚焦。振荡器功率和引出电压都存在最佳值。     

Development of exploding wire ion source for intense pulsed heavy ion beam accelerator

A Novel exploding wire type ion source device is proposed as a metallic ion source of intense pulsed heavy ion beam (PHIB) accelerator. In the device, multiple shot operations are realized without breaking the vacuum. The basic characteristics of the device are evaluated experimentally with an aluminum wire of diameter 0.2 mm and length 25 mm. A capacitor bank of capacitance 3 μF and a charging voltage of 30 kV was used, and the wire was successfully exploded by a discharge current of 15 kA with a rise time of 5.3 μs. Plasma flux of ion current density around 70 A/cm² was obtained at 150 mm downstream from the device. The drift velocity of ions evaluated by a time-of-flight method was 2.7×10⁴ m/ s, which corresponds to the kinetic energy of 100 eV for aluminum ions. From the measurement of the ion current density distribution, the ion flow is found to be concentrated toward the direction where the ion acceleration gap is placed. From the experiment, the device is found to be acceptable for applying the PHIB accelerator.     

射频离子源离子束成分光谱测量

为HL-2A 装置中性束注入器研制了引出束功率为1MW 的射频离子源。在测试平台上,实验离子源已经成功引出了束能量和束电流分别为35keV 和12.4A、束质子比为79%、脉宽为100ms 的氢离子束,达到了设计束功率要求的44%。在射频离子源实验平台上,利用多普勒频移光谱方法测量了离子源引出束流成分比例,对比了束流成分和射频离子源引出束流之间的关系。实验数据分析表明,在10A 引出束流的情况下,离子流成分 H⁺ ₁、H⁺ ₂ 和H⁺ ₃ 分别为75%、18%和7%。并且当引出束流从3.3A 升至10.4A 时,H⁺ ₁ 从37%升至78%,而H⁺ ₃ 则从19%降至9%。     

用于静电加速器的高频离子源及其引出特性

根据离子束生物工程的需要,设计和研制了一台用于静电加速器的小型高频离子源。针对使用环境从理论上确定了离子源的结构和尺寸。通过实验调试取得了引出束流与引出电压、聚焦电压以及放电气压之间的变化特性曲线,测定了引出束流的束径包络,对束流的不稳定性进行了分析,在设计中采取了有效的措施抑制束流不稳定性。结果表明,离子源的最佳工作条件为引出电压1 600V~1 800V,放电气压在（4~8）×10-4Pa范围,此时离子源可引出最大束流30μA。束流大小及其稳定性均达到预期要求。     

Ionization Scheme Development at the ISOLDE RILIS

The resonance ionization laser ion source (RILIS) of the ISOLDE on-line isotope separation facility is based on the method of laser step-wise resonance ionization of atoms in a hot metal cavity. The atomic selectivity of the RILIS complements the mass selection process of the ISOLDE separator magnets to provide beams of a chosen isotope with greatly reduced isobaric contamination. Using a system of dye lasers pumped by copper vapour lasers, ion beams of 24 elements have been generated at ISOLDE with ionization efficiencies in the range of 0.5–15%. As part of the ongoing RILIS development off-line resonance ionization spectroscopy studies carried out in 2003 and 2004 have determined the optimal three-step ionization schemes for scandium, antimony, dysprosium and yttrium.     

Laser ion source activities at Brookhaven National Laboratory

In Brookhaven National Laboratory (BNL), we have been developing laser ion sources for diverse accelerators. Tabletop Nd:YAG lasers with up to several Joules of energy are mainly used to create ablation plasmas for stable operations. The obtained charge states depend on laser power density and target species. Two types of ion extraction schemes, direct plasma injection scheme (DPIS) and conventional static extraction, are used depending on the application. We optimized and selected a suitable laser irradiation condition and a beam extraction scheme to meet the requirement of the following accelerator system. We have demonstrated to accelerate more than 5?×?10¹⁰ of C⁶⁺ ions using the DPIS. We successfully commissioned a low-charge ion beam provider to the user facilities in BNL. To achieve higher current, higher charge state and lower emittance, further studies will continue.     

强流激光离子源中的等离子体参数诊断

强流激光离子源是最有希望为重离子聚变直线感应加速器提供离子的离子源之一。离子源内等离子体决定了离子源性能和引出品质,为了了解强流激光离子源内等离子体参数,采用发射光谱和ICCD成像的方法对该离子源中的等离子体进行了诊断。该离子源由一台四倍频的266 nm Nd:YAG激光器和Cu靶组成,激光束经过透镜聚焦后照射在Cu靶上产生等离子体,激光打靶能量密度约为108 W/cm2,持续时间15 ns。ICCD相机拍摄了激光照射后等离子体的膨胀过程,初始时刻等离子体垂直表面喷射,膨胀速度约为1 cm/s。光谱仪测量了离子发射光谱,谱线主要由Cu原子的Cu Ⅰ谱线和Cu+离子的Cu Ⅱ谱线组成。采用Boltzmann图法得到膨胀等离子体电子激发温度约为1 eV,采用Stark展宽法得到电子密度约为1016 cm-3。     

State selective detection of sputtered Al neutrals by resonant laser ionization SNMS

It is important to optimize the resonance ionization efficiency of the sputtered particle by evaluating the internal energy of it. And also the dependence of the change of the internal energy of it on primary ion species and accelerating voltages was investigated. For this study, we developed proto-type resonance laser ionization SNMS instrument, which is a quadrupole SIMS apparatus combined with a wavelength tunable laser. The internal energy of the sputtered aluminum atoms, which has lowly lying excited state (112 cm⁻¹) on the ground state, was monitored. As the results, the internal energy of the sputtered aluminum atoms was not influenced by the change of the surface work function and primary ion beam energy at all. On the contrary, the density on lowly lying excited state drastically increased due to the existence of the oxygen on aluminum surface.     

Development of a RILIS ionisation scheme for gold at ISOLDE, CERN

At the ISOLDE on-line isotope separation facility, the resonance ionisation laser ion source (RILIS) can be used to ionise reaction products as they effuse from the target. The RILIS process of laser step-wise resonance ionisation of atoms in a hot metal cavity provides a highly element selective stage in the preparation of the radioactive ion beam. As a result, the ISOLDE mass separators can provide beams of a chosen isotope with greatly reduced isobaric contamination. With the addition of a new three-step ionisation scheme for gold, the RILIS is now capable of ionising 26 of the elements. The optimal scheme was determined during an extensive study of the atomic energy levels and auto-ionising states of gold, carried out by means of in-source resonance ionisation spectroscopy. Details of the ionisation scheme and a summary of the spectroscopy study are presented.     

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.