Ion storage at eV energies in an octopole ring

To store ions for times up to several seconds with energies in the 10 eV/amu range a tabletop storage ring with a circumference of about 1 m will be constructed. The ions will be confined and guided by RF-multipoles. The first objective is the production of pure ground state beams of (multiply charged) ions. This will allow for elucidating the unknown rule of metastable ions in electron capture studies, which will be performed in a crossed beam experiment after extraction of the ion beam from the storage ring. In order to test the technique of ion storage by means of RF-multipoles a linear RF-octopole beam guide has been constructed. First results of highly charged ion injection and subsequent electron capture studies in the RF-octopole beam guide are presented for C⁴⁺ ions.     

离子俘获的线性理论及其应用

从线性理论出发,研究了电子束团在储存环里均匀分布和束团串两种情况下离子俘获的条件;在离子系统里引入Twiss参量,推导出电子束团串俘获离子的阈值流强的公式;并以此讨论北京正负电子对撞机(BEPC)在同步辐射专用运行时观察到的电子束流现象,提出采用束团串运行来克服BEPC中的束流寿命下降.     

Coherent interaction of ion and electron beams in systems with electron cooling

A hydrodynamic approximation is used to study the behavior of dipole modes of the transverse oscillations of an ion beam in a storage ring with an electron cooling section. It is shown that in addition to the finite interaction time of the beams, instability may be caused by a specific interaction effect between the ion and electron beams in the magnetic field which leads to redistribution of energy between the various modes of the ion beam oscillations. In this case, the condition that the determinant of the transfer matrix for the cooling section does not exceed unity no longer guarantees the stability of the transverse coherent oscillations of the ion beam and all the eigenvalues of the complete matrix of the ion motion including the storage ring must be analyzed. Calculations of the stability of ion beam dipole oscillations are presented for the parameters of CELSIUS.     

HIRFL-CSR主环电子冷却模拟计算

以¹⁶O⁸⁺为例,用电子冷却模拟程序计算了冷却时间随离子能量、初始发射度、初始动量分散、离子流强以及离子电荷态的变化规律,研究了储存环在冷却段的β函数和色散函数对冷却时间的影响.     

Suppression of intrabeam scattering in cooled heavy ion beams

The properties of electron cooled heavy ion beams in the ESR storage ring are dominated by heating due to intrabeam scattering. For low intensity ion beams a sudden reduction of the longitudinal ion beam temperature has been detected by Schottky noise analysis. This can be interpreted as the disappearance of intrabeam scattering heating which could allow a longitudinal ordering of the ion beam.     

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.     

Progress in stored ion beam experiments on atomic and molecular processes

Stored fast ion beams in atomic and molecular collision experiments are discussed with an emphasis on electron–ion interactions at low relative energies. Recent progress was obtained in electron collision spectroscopy using an electron-cooled stored ion beam and a separate electron target in the same storage ring; from a cryogenic photocathode, electron beams with internal temperatures of 5 to 10 K were produced. Results are presented for dielectronic recombination resonances, resolving the hyperfine structure of stored lithiumlike scandium ions and obtaining precise results for the fine structure splitting of these ions, and for ro-vibrational resonances in the recombination of electrons with hydrogen molecular ions, revealing sharp structures down to 2 meV. An overview of the cryogenic storage ring (CSR) project in Heidelberg is given.     

High yields from the Stockholm electron beam ion source CRYSIS

CRYSIS is an electron beam ion source (EBIS) with a superconducting solenoid. Highly charged ions are delivered to the acceleration and storage ring CRYRING [ K. Abrahamsson et al., Nucl. Instr. Methods B 79 (1993) 269.], SMILETRAP [C. Carlberg et al., Phys. Scr. T 59 (1995) 196.] and to low energy atomic and surface physics experiments. Stable electron beam currents up to 700 mA are obtained, in order to enhance the ion yield out of the EBIS. Measurements of the total charge per pulse at different working conditions and electron beam current density measurements were done. At electron beam currents of 600 mA yields up to 2.5 × 10¹⁰ charges per pulse could be measured. This revised version was published online in August 2006 with corrections to the Cover Date.     

High-resolution dissociative recombination of cold H3+and first evidence for nuclear spin effects

The energy-resolved rate coefficient for the dissociative recombination (DR) of H(3)(+) with slow electrons has been measured by the storage-ring method using an ion beam produced from a radiofrequency multipole ion trap, employing buffer-gas cooling at 13 K. The electron energy spread of the merged-beams measurement is reduced to 500 microeV by using a cryogenic GaAs photocathode. This and a previous cold- measurement jointly confirm the capability of ion storage rings, with suitable ion sources, to store and investigate H(3)(+) in the two lowest, (J,G) = (1,1) and (1,0) rotational states prevailing also in cold interstellar matter. The use of para-H(2) in the ion source, expected to enhance para-H(3)(+) in the stored ion beam, is found to increase the DR rate coefficient at meV electron energies.     

Absolute measurement of electron-cloud density in a positively charged particle beam

Clouds of stray electrons are ubiquitous in particle accelerators and frequently limit the performance of storage rings. Earlier measurements of electron energy distribution and flux to the walls provided only a relative electron-cloud density. We have measured electron accumulation using ions expelled by the beam. The ion energy distribution maps the depressed beam potential and gives the dynamic cloud density. Clearing electrode current reveals the static background cloud density, allowing the first absolute measurement of the time-dependent electron-cloud density during the beam pulse.     

Enhancement of low energy electron-ion recombination in a magnetic field: influence of transient field effects

Electron-ion recombination observed in storage ring experiments shows a strong enhancement relative to what standard radiative recombination rates predict. We simulate the effect of a transient motional electric field induced by the merging of an electron and an ion beam in the electron cooler which opens an additional pathway for free-bound transitions of electrons. We show that the measured rate contains a significant contribution from radiative stabilization of Rydberg states formed by this transient motional electric field. The absolute excess recombination rates obtained are in good agreement with the experimental data. The scaling of the rate with the ion charge and the magnetic guiding field is analyzed.     

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.     

Theory of the polarization of highly charged ions in storage rings: Production, preservation, observation and application to the search for a violation of the fundamental symmetries

Theoretical concepts for the production, preservation and control of polarized highly charged ion beams in storage rings are investigated. It is argued that hydrogen-like ions can be polarized efficiently by optical pumping of the Zeeman sublevels of ground state hyperfine levels and that the maximum achievable nuclear polarization exceeds 90%. In order to study the preservation of the polarization during the ion motion through the magnetic system of the ring, the concept of the instantaneous quantization axis is introduced. It is suggested that the employment of “Siberian snakes” may help to preserve the ion beam polarization in the ring. The control of the beam polarization can be achieved by different methods: by measuring the Stokes parameters for the emitted photons or by observing the angular dependence of the transition rates for polarized ions. The important motivation for the production of polarized ion beams is the possibility to observe parity nonconservation effects in the hyperfine-quenched transitions in helium-like highly charged ions, where these effects can reach an unprecedented high value for atomic physics. The possible observation of parity nonconservation effects connected with the nuclear anapole moment is also discussed. A method for the observation of the electric dipole moment of an electron in a storage ring with a polarized highly charged ion beam is proposed. This method allows, in principle, to improve the existing boundaries for the electric dipole moment of an electron. However, the requirements of the corresponding experiment are very stringent.     

Electron scattering based on a novel internal target technique: SCRIT

A novel technique for forming internal targets, named SCRIT (Self-Confining RI Ion Target), has been developed, which can make electron scattering off short-lived radioactive nuclei possible in an electron storage ring. SCRIT confines the ions of interest by utilizing the “ion trapping” phenomenon in the electron storage ring. Approximately 10⁷ stable ¹³³Cs ions were trapped in a three-dimensional configuration along the electron beam axis at an electron beam current of 75mA. The angular distribution of the electrons scattered from the trapped ¹³³Cs ions was successfully measured, and a collision luminosity of 10²⁶/(cm² s) was achieved.     

Numerical simulation of particle dynamics in a storage ring by using BETACOOL program

The BETACOOL program, developed by electron cooling group of the Joint Institute for Nuclear Research (JINR), is a set of algorithms based on common format of input and output files. The program is oriented toward simulation of the ion beam dynamics in a storage ring in the presence of cooling and heating effects. The version presented in this report includes three basic algorithms: simulation of root-mean-square (rms) parameters of the particle distribution function evolving in time, simulation of the distribution function evolution using the Monte Carlo method, and a tracking algorithm based on a molecular dynamics technique. The general processes investigated with the program are intrabeam scattering in the ion beam, electron cooling, and interaction with residual gas and an internal target.     

Beam dynamics in an ultra-low energy storage rings (review of existing facilities and feasibility studies for future experiments)

Storage rings operating at ultra-low energies and in particular electrostatic storage rings have proven to be invaluable tools for atomic and molecular physics. Due to the mass independence of the electrostatic rigidity, these machines are able to store a wide range of different particles, from light ions to heavy singly charged bio-molecules. However, earlier measurements showed strong limitations on beam intensity, fast decay of ion current, reduced life time etc. The nature of these effects was not fully understood. Also a large variety of experiments in future generation ultra-low energy storage and decelerator facilities including in-ring collision studies with a reaction microscope require a comprehensive investigation of the physical processes involved into the operation of such rings. In this paper, we present review of non-linear and long term beam dynamics studies on example of the ELISA, AD Recycler, TSR and USR rings using the computer codes BETACOOL, OPERA-3D and MAD-X. The results from simulations were benchmarked against experimental data of beam losses in the ELISA storage ring. We showed that decay of beam intensity in ultra-low energy rings is mainly caused by ion losses on ring aperture due to multiple scattering on residual gas. Beam is lost on ring aperture due to small ring acceptance. Rate of beam losses increases at high intensities because of the intra-beam scattering effect adds to vacuum losses. Detailed investigations into the ion kinetics under consideration of the effects from electron cooling and multiple scattering of the beam on a supersonic gas jet target have been carried out as well. The life time, equilibrium momentum spread and equilibrium lateral spread during collisions with this internal gas jet target were estimated. In addition, the results from experiments at the TSR ring, where low intensity beam of CF⁺ ions at 93 keV/u has been shrunk to extremely small dimensions have been reproduced. Based on these simulations, conditions for stable ring operation with extremely low emittance beam are presented. Finally, results from studies into the interaction of ions with a gas jet target at 3–30 keV energy range are summarized.     

Novel internal target for electron scattering off unstable nuclei

A novel internal target has been developed, which will make electron scattering off short-lived radioactive nuclei possible in an electron storage ring. An "ion trapping" phenomenon in the electron storage ring was successfully utilized for the first time to form the target for electron scattering. Approximately 7 x 10(6) stable 133Cs ions were trapped along the electron beam axis for 85 ms at an electron beam current of 80 mA. The collision luminosity between the stored electrons and trapped Cs ions was determined to be 2.4(8) x 10(25) cm(-2) s(-1) by measuring elastically scattered electrons.     

Bunch beam cooling

Electron cooling is used for damping both transverse and longitudinal oscillations of heavy particle. The cooling of bunch ion beam (with RF voltage on) is important part of experiments with inner target, ion collision system, stacking and RF manipulation. The short length of an ion bunch increases the peak luminosity, gives a start-time point for using of the time-of-flight methods and obtains a short extraction beam pulse. This article describes the review of last experiments with electron cooling carried out on the CSRm, CSRe (China) and COSY (Germany) storage rings. The accumulated experience may be used for the project of electron cooler on 2.5 MeV (NICA) and 0.5 MeV HIAF for obtaining high luminosity, depressing beam-beam effects and RF manipulation.     

Large scale silver nanowires network fabricated by MeV hydrogen(H~+) ion beam irradiation

A random two-dimensional large scale nano-network of silver nanowires(Ag-NWs) is fabricated by MeV hydrogen(H~+) ion beam irradiation. Ag-NWs are irradiated under H~+ion beam at different ion fluences at room temperature. The Ag-NW network is fabricated by H~+ion beam-induced welding of Ag-NWs at intersecting positions. H~+ion beam induced welding is confirmed by transmission electron microscopy(TEM) and scanning electron microscopy(SEM). Moreover, the structure of Ag NWs remains stable under H~+ion beam, and networks are optically transparent. Morphology also remains stable under H~+ion beam irradiation. No slicings or cuttings of Ag-NWs are observed under MeV H~+ion beam irradiation.The results exhibit that the formation of Ag-NW network proceeds through three steps: ion beam induced thermal spikes lead to the local heating of Ag-NWs, the formation of simple junctions on small scale, and the formation of a large scale network. This observation is useful for using Ag-NWs based devices in upper space where protons are abandoned in an energy range from MeV to GeV. This high-quality Ag-NW network can also be used as a transparent electrode for optoelectronics devices.     

Calculation of the charge composition of an ion beam from an E-Mevva source

The charge composition of an ion beam from an E-Mevva source is calculated within a model of sequential electron ionization of ions in a vacuum arc plasma. The effect of the plasma initial parameters on the charge composition of the ion beam is studied. Possible charge compositions for more than 30 elements omitted from this article are estimated. Also, the charge composition of the ions is calculated for the ultimate current density of the electron beam.