The 18th International Conference on Ion Sources



No. 1 Beibinhe East Road, Chengguan District, Lanzhou
Zhao Hongwei (IMP)
    • 16:00 17:50
    • 18:00 21:00
    • 08:30 08:55
    • 09:00 09:30
      Opening Ceremony
    • 09:30 10:00
      Keynote Speaker: Wenlong Zhan (CAS)
    • 10:05 10:30
      Review of high intensity ion source development and operation for worldwide nuclear science facility 25m

      The Electron Cyclotron Ion Source (ECRIS) has transformed the nuclear physics research field over the last 40+ years. Today the performance of ECRIS sources are the first parameter that defines the design of new facilities and the performance of existing facilities. In this talk, I will review the current ‘state of the art’ performance capabilities for ECR ion sources and how those present capabilities form the primary design criteria for new facilities and set the limiting performance for existing facilities.

      Speaker: Dr Richard Pardo
    • 10:30 10:50
      Conference Photo
    • 10:50 11:20
      Coffee Break
    • 11:20 11:40
      Estimating Ion Confinement Times from Beam Current Transients in Conventional and Charge Breeder ECRIS 20m

      High-precision measurements [1] of the Doppler broadening of ion spectral lines have indicated, that ions in an ECRIS plasma may obtain much higher temperatures than is conventionally believed, i.e. on the order of 10 eV. The temperature is also observed to be charge state dependent. The anomalous temperatures could plausibly be explained by assuming the electrostatic confinement of ions in a potential well within the plasma potential, caused by accumulated hot electrons in the plasma core [2, 3]. In this confinement scheme, the ions would obtain long cumulative confinement times, which would allow them to be heated in collisions with the cold electron population.

      In the work presented herein, the ion confinement time is probed using a transient method similar to that employed in [4, 5]: Material injection into a buffer plasma is pulsed, and the extracted, decaying beam current transients are analyzed to obtain an estimate for the ion confinement time. The method is applied both in an ECR charge breeder source where material injection is realized by direct 1+ injection of potassium, and in a conventional ECRIS using sputtering of copper into various buffer gases (O, He, Ar). The transient equation used for the data analysis is derived from the ion balance equation, and the validity of the assumptions made in its derivation are evaluated. The measurements from the two experimental campaigns analyzed for this work yielded mutually corroborative results: The confinement time is estimated to be on the order of tens of milliseconds for Cu and K ions at charge to mass ratios between 0.15 and 0.27, with higher charge states corresponding to longer confinement times.

      The long confinement times support the notion of electron-ion interaction as a source of the anomalous ion temperatures, and a qualitative model based on the electrostatic confinement and electron-drag heating is proposed to connect the ion temperatures to the confinement times. Understanding the confinement times of highly charged ions is important fundamentally, but also for the practical purpose of developing radioactive ion beams, which depend not only on fast and efficient ionization, but also on short ion confinement times, to prohibit the decay of the radioactive isotopes during the charge breeding process.

      Speaker: Mr Miha Marttinen (University of Jyväskylä)
    • 11:40 12:00
      Effects of magnetic configuration on hot electrons in SECRAL-II plasma 20m

      To investigate the hot electrons population in highly charged electron cyclotron resonance ion source (ECRIS), the axial emitted bremsstrahlung spectra, along with microwave signal emitted from the ECRIS plasma are measured on SECRAL-II (Superconducting ECR ion source with Advanced design in Lanzhou No. II) ion source. The evolution of the hot electrons spectral temperature, Ts, is studied through the variation of magnetic configuration. The experimental results have shown that when the ratio of the minimum field to the resonance field (i.e. Bmin /Becr) is less than 0.75~0.80, there is a linear dependence of the spectral temperature on the ratio of Bmin /Becr, above this threshold Ts saturates and electron cyclotron instability appears simultaneously. This phenomenon may be due to the fact that the spectral temperature Ts provides an indication of the temperature of the hot electrons, significant losses of the hot and warm electrons caused by electron cyclotron instability will lead to a saturation of Ts. In addition, this investigation has also shown that Ts decreases with the increase of the gradient at the resonance zone at low mirror ratio and is insensitive to the gradient at high mirror ratio when Bmin is constant.

      Speaker: Jibo Li
    • 12:00 12:20
      Evaluation method of plasma instability in laser ion source using solenoid 20m

      A laser ion source can provide stable intense heavy ion beams with relatively simple structure. Recently, solenoid confinement technique was developed and applied to the operating laser ion sources. By introducing solenoid, supplied ion beam current can be enhanced and adjusted for the applications. However, it is known that the expanding laser plasma confined by a solenoid filed becomes unstable in a certain magnetic field region. To investigate the unstable condition further, it is essential to quantify the instability. In this study, we propose the most appropriate method to evaluate plasma instability. The validity was evaluated by comparing five methods, variation of maximum value, variation of integral value, variation of half width, variation of half value width divided by maximum value, integral value of difference from average waveform. The detailed comparison discussion will be given at the presentation.

      Speaker: Takahiro Karino
    • 12:20 13:50
      Lunch Break
    • 14:00 14:30
      Measurements and Simulations of the Energy Distribution of Electrons Lost from the Minimum B-field 30m

      Further progress in the development of ECR ion sources (ECRIS) requires a deeper understanding of underlying physics. One of the topics that remains little studied, though being crucial for the confinement of the plasma and performance of the ion source, is the electron energy distribution (EED). A well-developed technique of measuring the EED of electrons escaping axially from a magnetically confined plasma of an ECRIS is reported. The majority of the experimental data were recorded in pulsed and CW discharges with a room-temperature 14 GHz ECRIS at the JYFL accelerator laboratory. It was discovered that for 14 GHz source the EED is strongly non-Maxwellian in the range of 5–250 keV and exhibits several local maxima below 20 keV energy. It was observed that the most influential ion source operating parameter on the EED is the magnetic field strength, which affected the EED predominantly at energies less than 100 keV. The effects of the microwave power and frequency on the EED were found to be less significant. The latter measurements were focused on distinguishing between the EED in stable plasma and the one perturbed with kinetic instabilities. It was found that nonlinear phenomena alter the energy distribution of the lost electrons noticeably. It has been shown earlier that the two-frequency plasma heating mode, being widely used, boosts the ECRIS performance presumably thanks to suppression of kinetic instabilities. We report the observed changes in EED of the escaping electrons introduced by the secondary frequency in different regimes, including the one with the secondary frequency being below the cold ECR in the magnetic trap. Discussion on the suppression mechanism of kinetic instabilities by means of applying the secondary frequency heating and the role of RF pitch angle scattering is presented along with the comparison of experimentally obtained EED to the simulated one with the use of NAM-ECRIS PIC code.

      Speaker: Dr Ivan Izotov (Institute of Applied Physics of Russian Academy of Sciences)
    • 14:30 15:00
      Self-Consistent Modeling of Beam-Plasma Interaction in the Charge Breeding Optimization Process 30m

      The slowing down and capture by a plasma of externally injected 1+ ions, as a consequence of very frequent elastic Coulomb collisions, is the main mechanism involved in the charge breeding process based on Electron Cyclotron Resonance Ion Sources. The INFN ion source group has been undertaking an intense activity on numerical simulations of the beam-plasma interaction, developing a code that has been proving to be very effective in reproducing several experimental results of charge breeding of light and heavy ions. This contribution will present the progress made in the development of the numerical code, focusing the attention on the latest simulations of charge breeding of Rb1+ ions employing a self-consistent plasma target model. The effect of the real plasmoid/halo structure on the capture process will be underlined, as well as the influence of different plasma excitation frequencies.

      Speaker: Dr Alessio Galatà (INFN-Legnaro National Laboratories)
    • 15:00 15:20
      Multi-diagnostics setup as a tool to overcome the limits of compact ion sources 20m

      The development of plasma diagnostics devoted to compact ion sources is being one of the main efforts of INFN-LNS ion source group for a decade. Indeed, the use of the brute force can lead to improvements in ion sources’ performances only if accompanied by a proper understanding of the plasma physics processes within the ion source. The key goal of plasma diagnostics in compact ion sources is the volumetric knowledge of the electron energy distribution function (EEDF) and the on-line evaluation of the plasma composition. This information will allow tuning EEDF to maximize the generation of the desired ion. Moreover, development of time resolved diagnostics has given precious information about the strategy for decreasing the beam ripple and increasing the operability domain of ion sources.
      The paper will introduce the most relevant diagnostics developed in the last ten years at INFN-LNS (optical emission spectroscopy, volume and space resolved X-ray diagnostics, RF and Langmuir probe diagnostics, interfero-polarimetric diagnostics) together with the main experimental results they have permitted to attain.
      Particular relevance will be also given to the perspectives and next goals of plasma diagnostics’applications.

      Speaker: Giuseppe Castro (INFN-LNS Via S. Sofia 62, 95123 Catania (Italy))
    • 15:20 15:40
      Particle-in-cell simulation of transport and energy deposition of intense proton beams in solid-density material 20m

      A complete particle-in-cell (PIC) simulation has, for the first time, been performed for the transport and energy deposition of an intense proton beam within a solid. In particular, for close interactions, we developed a novel Monte-Carlo binary collision model that takes into account all interactions between the incident protons and matter, e.g. proton-nuclei, proton-bound electron and proton-free electron. This includes especially also a Monte-Carlo model for the collisional ionization and electron-ion recombination as well as the depression of the ionization potential by surrounding charged particles. Moreover, we take into account collective electromagnetic effects by solving reduced Maxwell Equations. For intense proton beams, the collective electromagnetic effects ensure localized energy deposition by collimating proton beams, which would otherwise be deflected by the collisions with nucleus. This simulation model enables kinetic investigation of charged particle transport in high energy density plasmas.

      Speaker: Dr Dong Wu (Zhejiang University)
    • 15:40 16:00
      Upper Hybrid Resonance Heating Experiments on Electron Cyclotron Resonance Ion Source 20m

      We have been considered accessibility condition of electromagnetic and electrostatic waves propagating in ECR ion source (ECRIS) plasma, and then investigated their correspondence relationships with production of multicharged ions. It has been clarified that there exits efficient configuration of ECR zones for producing multicharged ion beams, and then has been suggested that new resonance, i.e. upper hybrid resonances (UHR), must have occurred.[1] We have been promoting new advanced experiments inducing actively these additional effects for enhanced furthermore multicharged ion beams with launching extra-ordinary (X) mode waves. Initially we had already conducted to applying 9GHz X-mode microwaves to 2.45GHz ECRIS, and it had been observed enhancements of higher energy tails of electron energy distributions function measured by the probe methods.[2] Next we have been trying similar experiments with 4-6GHz X-mode microwaves,[3] and we have succeeded in enhancing production of multicharged ions by launching these bands X-mode microwaves. Furthermore, at the same time we have observed sharp increases of electron energy distribution functions in ECRIS plasma by means of probe methods. It have been concluded that the UHR must have occurred by applying multiplex microwaves with their frequencies away from those for ECR in ECRIS. In this paper we will describe brief theoretical background and these new experimental results.

      References and Acknowledgment
      [1] Y. Kato, K. Yano, T. Nishiokada,, Review of Scientific Instruments, 87(2016)02A710-1-4.
      [2] T. Nishiokada, T. Nagaya, S. Hagino,, Review of Scientific Instruments, 87(2016)02A714-1-3.
      [3] Y. Kato, T. Nishiokada, T. Nagaya,, AIP Conference Proceedings 2011, 020005 (2018)
      The authors would like to thank Professor T. Asaji, National Institute of Technology, Toyama College, for preparations of additional microwave sources to be available in these works.

      Speaker: Yushi Kato (Osaka Univ.)
    • 16:00 16:20
      Measurement of the Energy Distribution of Electrons Escaping Confinement from an Electron Cyclotron Resonance Ion Source 20m

      The production of high charge state ions in electron cyclotron resonance ion sources (ECRIS) is dependent on the electron energy distribution (EED) within the source plasma. In order to better understand the EED a measurement of electrons escaping axially from an ECRIS device has taken place at the National Superconducting Cyclotron Laboratory (NSCL). Electrons were measured escaping from the Superconducting Source for Ions (SuSI), driven at 18 GHz. Dependencies of the observed EED on the confining magnetic field strength, injected microwave power, and neutral gas pressure were measured. Measurements of the axial bremsstrahlung spectrum were simultaneously measured to provide a direct comparison between both techniques. Results showed a large peak of electrons in the 600-1000 keV energy range. Calculations of the average electron energy and bremsstrahlung spectral temperature as a function of varying plasma parameters are also reported.

      Speaker: Mr Bryan Isherwood (Michigan State University/NSCL/FRIB)
    • 16:20 17:50
      Coffee Break: Poster Session - MonP C01, C06, C10
    • 08:30 09:00
      Overview of High Intensity Ion Source Development in the Past 20 Years at IMP 30m

      In the past 20 years, obvious progress has been made with the IMP ion accelerator development in terms of high intensity, high energy and high power machines. We still foresee the facilities to be built in the near future, for instance HIAF (High Intensity heavy ion Accelerator Facility) and CiADS (China initiative ADS), and so on, which have strong demands of high intensity ion beams of H~U. High intensity ion source paves the way for the development of future ion accelerators. Therefore, continuous research and development work has been made at IMP to improve ion source performance by means of new machine developments and ion source physics investigations. For intense mono-charged ion beams, 2.45 GHz ion sources have been developed together with the low energy transmission lines. For intense CW/DC multiply charged ion beams production, high performance ECR ion sources have been developed with the operation frequencies of 14.5~45 GHz. As very high intensity pulsed ion beams could be used for synchrotron injection, especially of those of very refractory metals, laser ion source has also been introduced to IMP, and got remarkable progress in the past years with regards to ion beam intensities, charge states, and beam stabilities. This paper will give an overview of the high intensity ion source development at IMP, especially on the recent progresses and new results.

      Speaker: Liangting Sun (Institute of Modern Physics, CAS)
    • 09:00 09:30
      Overview of high intensityRHIC-EBIS for the BNL heavy ion program 30m
      Speaker: Mr Edward Bebee
    • 09:30 09:50
      Production of intense metal ion beam with RIKEN 28 GHz SC-ECRIS 20m

      To produce intense metal ion beams (e.g. Ti13+, V12+,13+, U35+ ) for super-heavy element search and RIBF experiments at RIKEN, we tried to optimize the RIKEN 28 GHz SC-ECRIS performance. We systematically measured the beam intensity of various heavy ions as a function of Binj, Br and Bext with 14, 18 and 28 GHz microwaves for various heavy ions. In these experiments, we observed that (1) optimum Binj>1.6~2 Bext, (2) optimum Br>1.2~1.4 Bext and (3) optimum Bext is dependent on the charge state.
      Using this systematics, we obtained ~400emicroA of V13+ at low RF power of ~2kW and very low magnetic field (Bext~1.4 T with 28 GHz). For long term operation (one month), we successfully produced very stable beam of 100~200 e micro A of V13+ ion. Based on the systematics, we also produced ~225 e micro A of U33+ ion beam and ~200 e micro A of U35+ ion beam at only 2.2~2.6 kW of RF power.
      In this contribution, we discuss the mechanism to obtain these systematics using simple model calculation. And we report the experimental results and how to produce intense metal ion (Ti, V, and U ions) beams in detail.

      Speaker: takahide Nakagawa (RIKEN)
    • 09:50 10:10
      Production of intense uranium beams with inductive heating oven at IMP 20m
      Speaker: Wang Lu (Institute of Modern Physics)
    • 10:10 10:30
      Stable short-pulse ion beam production with the laser ion source at IMP 20m
      Speaker: Dr Huanyu Zhao (Institute of Modern Physics)
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