高性能全永磁ECR离子源LAPECR2的研制

研制了一台体积和重量都较大、设计性能较高的全永磁电子回旋共振(Electron cyclotron resonance,ECR)离子源LAPECR2(Lanzhou all permanent magnetic ECRion source No.2 ).该离子源将用于中国科学院近代物理研究所320 kV高压平台,为其提供强流高电荷态离子束流.LAPECR2的研制采用全新的全永磁磁体结构设计,通过采用高性能的NdFeB永磁材料、优化的磁结构设计以及精确的计算,实测源体的磁场参数能达到高性能ECR离子源的设计要求.离子源采用较高频率的14.5 GHz微波馈入加热等离子体,波导直接馈入离子源以增强馈入微波的稳定性与效率.此外,还大量采用了一些有利于提高离子源高电荷态离子产额的关键技术,如铝内衬等离子体弧腔、负偏压盘、铝制等离子体电极、三电极引出系统、辅助掺气等.     

全永磁ECR离子源研究进展

ECR(电子回旋共振)离子源是产生稳定的强流多电荷态离子束流最有效装置.全永磁ECR离子源因其独特的特点为很多中小型多电荷态离子束流实验平台与离子注入机等系统所采用,为后者产生重复性好、稳定性强的多电荷态离子束流.本文着重论述了中国科学院近代物理研究所研制的几台全永磁多电荷态ECR离子源及其特性与典型性能,如能产生强流高电荷态离子束流的高性能全永磁离子源LAPECR2,能产生强流中低电荷态离子束流的LAPECR1,能产生多电荷态重金属离子柬流的LAPECRl-M等.这些性能稳定的离子源为提高近代物理研究所相关试验平台的性能提供了关键的束流品质保障.     

Scintillation light produced by low-energy beams of highly-charged ions

Measurements have been performed of scintillation light intensities emitted from various inorganic scintillators irradiated with low-energy beams of highly-charged ions from an electron beam ion source (EBIS) and an electron cyclotron resonance ion source (ECRIS). Beams of xenon ions Xe^q+ with various charge states between q = 2 and q = 18 have been used at energies between 5 and 17.5 keV per charge generated by the ECRIS. The intensity of the beam was typically varied between 1 and 100 nA. Beams of highly charged residual gas ions have been produced by the EBIS at 4.5 keV per charge and with low intensities down to 100 pA. The scintillator materials used are flat screens of P46 YAG and P43 phosphor. In all cases, scintillation light emitted from the screen surface was detected by a CCD camera. The scintillation light intensity has been found to depend linearly on the kinetic ion energy per time deposited into the scintillator, while up to q = 18 no significant contribution from the ions’ potential energy was found. We discuss the results on the background of a possible use as beam diagnostics, e.g. for the new HITRAP facility at GSI, Germany.     

Study of a new cusp field for an 18 GHz ECR ion source

A feasibility study was performed to generate new sufficient mirror cusp magnetic field (CMF) by using the coils of the existing room temperature traditional 18 GHz electron cyclotron resonance ion source (ECRIS) at RIKEN. The CMF configuration was chosen because it contains plasma superbly and no multipole magnet is needed to make the contained plasma quiescent with no magneto-hydrodynamic (MHD) instability and to make the system cost-effective. The least magnetic field, 13 kG is achieved at the interior wall of the plasma chamber including the point cusps (PC) on the central axis and the ring cusp (RC) on the mid-plane. The mirror ratio calculation and electron simulation were done in the computed CMF. It was found to contain the electrons for longer time than in traditional field. It is proposed that a powerful CMF ECRIS can be constructed, which is capable of producing intense highly charged ion (HCI) beam for light and heavy elements.     

Versatile plasma ion source with an internal evaporator

A novel construction of an ion source with an evaporator placed inside a plasma chamber is presented. The crucible is heated to high temperatures directly by arc discharge, which makes the ion source suitable for substances with high melting points. The compact ion source enables production of intense ion beams for wide spectrum of solid elements with typical separated beam currents of ∼100-150 μA for Al⁺, Mn⁺, As⁺ (which corresponds to emission current densities of 15-25 mA/cm²) for the extraction voltage of 25 kV. The ion source works for approximately 50-70 h at 100% duty cycle, which enables high ion dose implantation. The typical power consumption of the ion source is 350-400 W. The paper presents detailed experimental data (e.g. dependences of ion currents and anode voltages on discharge and filament currents and magnetic flux densities) for Cr, Fe, Al, As, Mn and In. The discussion is supported by results of Monte Carlo method based numerical simulation of ionisation in the ion source.     

The influence of the charged back side on the transmission of highly charged ions through PC nanocapillaries

We have measured the fraction of the ions transmitted through nanocapillaries with their initial charge state for 200 keV Xe⁷⁺ ions impact on a polycarbonate (PC) foil with a thickness of 30 μm and a diameter of 150 nm. An Au film was evaporated on both the front and back side. It is found that more than 97% of the transmitted ions remain in their initial charge state. Then, the transmitted ion fraction and the characteristic tilt angle of 40 keV Xe⁷⁺ ions through this foil and another one with the same thickness and diameter, but evaporated by Au only on the front side, were measured. By comparing the results of these two foils, the influence of the ions deposited in the capillary exit region on the transmitted ion fraction and the characteristic tilt angle is studied. In comparison with the foil evaporated by Au on both sides, the maximum transmitted ion fraction of the foil evaporated by Au on the front side only is nearly 4 times smaller. Also, the characteristic tilt angle is slightly decreased. These results are discussed within the models for the guiding effect.     

Software for automatization of IEA-analysis of plasma-laser spectra

A software has been developed in order to automatize the ion energy analyzer (IEA) spectra analysis of laser-generated plasmas.A Nd:Yag laser operating at an intensity of the order of 10¹⁰ W/cm², 9 ns pulse width and energy of the order of 600 mJ, has been employed to irradiate different metallic targets (Al, Ti, W) and to produce plasma pulses. The ion emission from the plasma is monitored through an IEA instrument permitting time-of-flight (TOF) measurements to determine the ion energy distributions as a function of the charge state.The software program consists in two sections. The first one permits to identify the IEA ion peaks corresponding to different charge states as a function of the theoretical TOF values. The second section permits to plot the ion velocity and energy distributions as a function of the charge state. The obtained distributions are fitted using the “Coulomb-Boltzamnn shifted” function approach through the “Peakfit” code. The fit of the experimental data permits to estimate the equivalent plasma temperature and the average energy shift of the distributions as a function of the ion charge state.     

Physics design of a 70 MeV high intensity cyclotron, CYCIAE-70

This paper introduces the physics design of a 70 MeV high intensity cyclotron at China Institute of Atomic Energy (CIAE), which is aimed for multiple uses including radioactive ion-beam (RIB) production. The machine adopts a compact structure of four straight sectors, capable of accelerating two kinds of beams, i.e. H⁻ and D⁻ . The proton and deuteron beam will be extracted in dual opposite directions by charge exchange stripping devices. The energy of the extracted proton beam is in the range 35-70 MeV with an intensity up to 700 μA. The corresponding values for the deuteron beam are 18-33 MeV and 40 μA. This paper will present the main characteristics and parameters in the design of the 70 MeV cyclotron, the results of the basic beam dynamics study, as well as the physics in the design of the different systems, including the main magnet, RF, injection and extraction systems, etc.     

2.45GHz单电荷态电子回旋共振离子源

描述了一台2．45GHz单电荷态电子回旋共振（ECR）离子源的原理、结构与应用。介绍了其微波系统与磁场结构。在微波输入功率约600W,引出高压22kV,引出孔径为φ6mm时,该离子源的总束流I（H1^ H2^ H3^ )可达90mA。     

Overall design of CYCIAE-14, a 14 MeV PET cyclotron

Based on a 10 MeV CRM cyclotron developed at China Institute of Atomic Energy (CIAE) with an achieved beam intensity of up to 430 μA, a 14 MeV high intensity compact cyclotron, CYCIAE-14, was designed and being built at CIAE. It is planned that the first machine would be in place with a span of 2 years. CYCIAE-14 is delicately designed to realize strong vertical focusing by adopting a 4-sector, variable hill-gap structure with an external ion source to achieve high intensity. A special design applied to the stripping extraction gives access to dual extraction with four beams. The adoption of sophisticated industrial technology will give the cyclotron advantages, e.g. low power consumption and high reliability. This paper is aimed to present the overall design of the machine, including the basic technical specifications, main magnet and coils, RF, ion source and axial injection, and stripping extraction, etc. It will also give an introduction to its construction schedule as well as the up-to-date progress.     

Identification of the ECR zone in the SWISSCASE ECR ion source

The magnetic field of the permanent magnet electron cyclotron resonance (ECR) ion source SWISSCASE located at the University of Bern has been numerically simulated and experimentally investigated. For the first time the magnetized volume qualified for electron cyclotron resonance at 10.88 GHz and 388.6 mT has been analyzed in highly detailed 3D simulations with unprecedented resolution. The observed pattern of carbon coatings on the source correlates strongly with the electron and ion distribution in the ECR plasma of SWISSCASE. Under certain plasma conditions the ion distribution is tightly bound to the electron distribution and can considerably simplify the numerical calculations in ECR related applications such as ECR ion engines and ECR ion implanters.     

Imaging dynamics of charge-auto-organisation in glass capillaries

Multiply charged ion beam transmission through insulating capillaries is today a very active field of research. Thanks to the work of several groups during the last five years, several features of this unexpected process have been evidenced. The open challenge is to understand and control the self-organized charging-up of the capillary walls, which leads finally to the ion transmission. Up to now, the specific charge distribution on the inner surface, as well as the dynamics of the build-up, are still to be understood. While capillaries usually studied are microscopic pore networks etched in different materials, our concern is in macroscopic single capillaries made of glass. With a length of several centimeters and a diameter of a few micrometers at the exit, these capillaries have nevertheless the same aspect ratio as the etched pores (length/diameter ≈ 100). One of the leading goals of this research on single capillaries is to produce multi-charged ion beams with diameters smaller than a micrometer (nano-beams). These glass capillaries offer the opportunity to be used as an ion funnel due to their amazing properties of guiding and focusing highly charged ion beams without altering neither their initial charge state nor the beam emittance (<10⁻³ π mm mrad). However, the understanding of the underlying process is not complete and relies on models assuming charge patches distributed along the capillary and which still need to be tested. We present the first observation imaging the dynamics of the charging-up process in single glass capillaries. During the build-up of the self-organized charge deposition on the capillary walls, the 230 keV Xe²³⁺ transmitted beam is deflected back and forth several times as the outgoing current increases. This is in agreement with the picture of charge patches created sequentially along the capillary and thus deflecting the beam until a stationary state is reached.     

Irradiation effects of a 10 MeV neutron beam on a Nd-Fe-B permanent magnet

The effects of irradiation of a Nd-Fe-B permanent magnet by fast neutrons was investigated. The decrease in measured magnetic flux density at the center of the magnets were 0.6%, 6.9%, 25.2% and 47.3% after continuous irradiation of 1.1 kGy, 3.7 kGy, 5.6 kGy and 7.4 kGy, respectively. On the other hand, the decrease due to non-continuous irradiation, in which the magnet was first irradiated at 3.7 kGy, then irradiated again at 3.7 kGy nine months later, was 14% smaller than that of continuous irradiation, even for the same total dose. The temperature coefficient of the magnetization did not change with irradiation. Some radioactive materials, such as ¹⁴⁷Nd, ¹⁵¹Pm, and ⁵⁴Mn, were detected in the magnet after irradiation.     

Optogalvanic spectroscopy using 389 nm coherent light source accurately tuned to resonance frequency of 2S->3P of He

An efficient 389 nm coherent light source, made possible through the single-pass second-harmonic generation of a picosecond Ti:sapphire laser with a periodically poled lithium niobate waveguide, was developed for the metastability exchange optical pumping of hyperpolarized ³He gas, which is applicable to imaging with nuclear magnetic resonance. The second-harmonic light provided such a broad spectrum that some split sub-levels of its metastable state under an applied magnetic field could be pumped efficiently and simultaneously. Optogalvanic spectroscopy using the light source indicated that the spectral width of ³He was much less than 70 GHz, which was similar to the spectral width of the light source.     

A sextupole ion beam guide to improve the efficiency and beam quality at IGISOL

The laser ion source project at the IGISOL facility, Jyväskylä, has motivated the development and construction of an rf sextupole ion beam guide (SPIG) to replace the original skimmer electrode. The SPIG has been tested both off-line and on-line in proton-induced fission, light-ion and heavy-ion induced fusion-evaporation reactions and, in each case, has been directly compared to the skimmer system. For both fission and light-ion induced fusion, the SPIG has improved the mass-separated ion yields by a factor of typically 4-8. Correspondingly, the transmission efficiency of both systems has been studied in simulations with and without space charge effects. The transport capacity of the SPIG has been experimentally determined to be ∼10¹² ions s⁻¹ before space charge effects start to take effect. A direct comparison with the simulation has been made using data obtained via light-ion fusion evaporation. Both experiment and simulation show an encouraging agreement as a function of current extracted from the ion guide.     

Synthesis of KNaSO4:Tb and MgSO4:Dy phosphors for lyoluminescence dosimetry

KNaSO₄:Tb³⁺ phosphors were synthesized by melt technique with different concentration of Tb³⁺ ions and MgSO₄:Dy³⁺ phosphor is prepared by solid state diffusion method. Lyoluminescence and photoluminescence characterization of KNaSO₄:Tb and MgSO₄:Dy³⁺ phosphors are reported in this paper. Only one sharp peak is observed in the lyoluminescence (LL) glow curve and KNaSO₄:Tb(0.05 mol%) phosphor shows maximum efficiency. The LL intensity increases linearly with gamma ray dose. LL emission occurs in the blue and yellow region of the spectrum. Photoluminescence (PL) characterization of KNaSO₄:Tb(0.05 mol%) phosphor shows PL emission at 486 and 546 nm. These PL emissions from KNaSO₄:Tb³⁺ are due to ⁵D₄ → ⁷F₆ and ⁵D₄ → ⁷F₅ transitions of Tb³⁺ ion respectively. Lyoluminescence of MgSO₄:Dy³⁺ phosphor shows the high sensitivity to γ-ray exposure and LL emission observed at 486 and 572 nm in the blue and yellow emission of the spectrum is due to Dy³⁺ ion. Experimental results obtained in the present investigation show that KNaSO₄:Tb³⁺ and MgSO₄:Dy³⁺ phosphors are suitable as a lyoluminescence dosimetry phosphor for ionizing radiations.     

Ion irradiation effects on tungsten-oxide films and charge state effect on electronic erosion

We have studied electronic- and atomic-structure modifications of polycrystalline WO₃ films (bandgap of ∼3 eV) by ion irradiation. WO₃ films were prepared by oxidation of W films on MgO substrates and of W sheets. We find disordering or amorphization, the lattice expansion of ∼1.5% and bandgap increase of 0.2 eV after 90 MeV Ni ion irradiation at ∼3 × 10¹² cm⁻². A broad peak of optical absorption appears around 1.6 μm by ion irradiation. We also find that the erosion yield by high-energy ions with the equilibrium charge exceeds 10⁴ and that the erosion yield under ion impact with non-equilibrium charge (90 MeV Ni⁺¹⁰) is ∼1/5 of that with the equilibrium charge (89 MeV Ni⁺¹⁹). Effects of depth dependence of the ion mean charge on the erosion yields are discussed. The erosion yield by low-energy ions is also presented.     

Neutron interrogation of high-enriched uranium by a 4 MeV linac

For revealing unauthorized transport (illicit trafficking) of nuclear materials, a non-destructive method reported earlier, utilizing a 4 MeV linear accelerator for photoneutron interrogation, was further developed. The linac served as a pulsed neutron source for assay of highly enriched uranium. Produced in beryllium or heavy water by bremsstrahlung, neutrons subsequently induced fission in the samples. Delayed neutrons were detected by a newly designed neutron collar built up of 14 ³He counters embedded in a polyethylene moderator. A PC controlled multiscaler served as a time analyzer, triggering the detector startup by the beam pulse. Significant progress was achieved in enhancing the detector response, hence the sensitivity for revealing illicit material. A lower sensitivity limit of the order of 10 mg ²³⁵U was determined in a 20 s measurement time with a reasonable amount of beryllium (170 g) or of heavy water (100 g) and a mean electron current of 10 μA. Sensitivity can be further enhanced by increasing the measurement time.     

Development of a high intensity Al beam from SiC targets for accelerated beam experiments at ISAC

An intense beam of ^26gAl has been developed for accelerated beam experiments at TRIUMF’s ISAC facility. Studies of the on-line production of Al radionuclides from thick silicon carbide targets have been performed as part of a program of beam development for astrophysical reaction studies at ISAC. While the release of short-lived Al nuclides from SiC was found to be slow, development of new target material forms and high-power target containers has allowed operation of SiC targets with proton currents of up to 70 μA on target. In addition, operation with the TRIUMF resonant ionization laser ion source (TRILIS) has produced ^26gAl beam intensities of 5.1 × 10¹⁰ s⁻¹.     

PL and XPS study of radiation damage created by various slow highly charged heavy ions on GaN epitaxial layers

Photoluminescence (PL) spectrum, in conjunction with X-ray photoelectron spectroscopy (XPS) is used to evaluate the surface damage of GaN layer by highly-charged Xe^q+ (18 ? q ? 30), Ar^q+ (6 ? q ? 16) and Pb^q+ (q = 25,35) ions. The intensity of PL emission of GaN layer, including near band-edge peak and yellow luminescence, decreases with increasing fluence and charge state of the incident ions. Finally the PL emission is completely quenched after irradiation to high fluences at high charge state. A new peak at 450 nm appeared in PL spectra of the specimens irradiated with Xe¹⁸⁺, Ar⁶⁺ and Ar¹¹⁺, indicating that radioactive recombination within donor-acceptor pairs (DAPs) during irradiation. After irradiation, XPS spectra show N deficient or Ga rich on GaN surface and XPS spectra of Ga3d core levels indicate spectral peak evidently shifts from a Ga-N to Ga-Ga and Ga-O bond. The relative content of Ga-N bond decreases and the content of Ga-Ga bond increases with the increase of ion fluence and ion charge state. The binding energy of Ga3d_5/2 electron corresponding to Ga-Ga bond of the irradiated GaN film is found to be smaller than that of metallic Gallium (Ga⁰), which can be attributed to irradiation damage.