A Wide-Range Soft-Switching AHB-Flyback Converter for Flat-Top Pulsed Magnetic Field Power Supplies

This paper proposes a single-stage asymmetrical half-bridge fly-back (AHBF) converter with resonant mode using dual-mode control. The presented converter has an integrated boost converter and asymmetrical half-bridge fly-back converter and operates in resonant mode. The boost-cell always operates in discontinuous conduction mode (DCM) to achieve high power factor. The presented converter operates simultaneously using a variable-frequency-controller (VFC) and pulse-width-modulation (PWM) controller. Unlike the conventional single-stage design, the intermediate bus voltage of this controller can be regulated depending on the main power switch duty ratio. The asymmetrical half-bridge fly-back converter utilizes a variable switching frequency controller to achieve the output voltage regulation. The asymmetrical half-bridge fly-back converter can achieve zero-voltage-switching (ZVS) operation and significantly reduce the switching losses. Detailed analysis and design of this single-stage asymmetrical half-bridge fly-back converter with resonant mode is described. A wide AC input voltage ranging from 90 to 264 Vrms and output 19 V/120 W prototype converter was built to verify the theoretical analysis and performance of the presented converter.

Worldwide several electron cyclotron resonance (ECR) ion sources have been developed and in operation for heavy ion accelerators using Nb-Ti superconducting magnets. The Versatile ECR ion source for NUclear Science (VENUS) at the Lawrence Berkeley National Lab (LBNL) and the newly commissioned 28 GHz superconducting ECR ion source at the Facility for Rare Isotope Beams (FRIB) were developed by LBNL. Both sources adopt a scheme with a sextupole magnet inside a mirror -type solenoid to confine the ions and electrons. Nb-Ti coils limit all the existing ECR ion sources to operate below ∼9 T at 4.2 K. Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> Sn potentially enables next generation ECR ion sources with a higher field limit (∼22 T at 4.2 K). As an example, a 45 GHz ECR ion source Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> Sn magnet is currently being developed by the Institute of Modern Physics (IMP) in China. Clearly conductor characteristics of Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> Sn are very much different and new development are needed to meet challenges such as coil fabrication. FRIB and LBNL team up again to develop ECR ion sources based on Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> Sn. Here as the first step, this paper describes the design of a second 28 GHz superconducting ECR ion source using Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> Sn coils at FRIB. We present conductor selection and characteristics, magnetic design, mechanical design and cold mass assembly, coil fabrication challenges and potential solution, quench protection, and the development and prototyping efforts so far.

Brief review of multiple charge state ECR ion sources in Lanzhou

Recent development of electron cyclotron resonance (ECR) ion sources in China is reviewed. Emphasis is put on high charge state ECR ion sources which have been mainly developed in China by Institute of Modern Physics (IMP). Presently two ECR ion sources built by IMP for highly charged ion beams are put into operation for cyclotrons and atomic physics research. The development of high charge state ECR ion sources at IMP has progressed with a new magnetic field configuration, better condition for extraction of highly charged ions, high mirror magnetic field, large plasma volume, and special techniques to provide extra cold electrons. These techniques greatly enhance the production of highly charged ions from IMP ECR ion sources. So far more than 185 eμA of Ar11+ and 50 eμA of Xe26+ were produced by the IMP ECR ion sources. The metallic ion beam production was tested and the first beam Ca11+40 was provided to the cyclotrons at IMP. The beam intensity of Ca11+40 could reach 130 eμA. The next part of this article will report the latest progress of 2.45 GHz ECR ion sources in China. A 2.45 GHz compact permanent magnet proton ion source was designed and constructed by IMP. A new microwave feeding system is applied on this ion source. The ion source is able to deliver 90 mA of mixed ion beam (H1++H2++H3+) after preliminary commissioning. The article also mentions a small 2.45 GHz ECR ion source which was built by Sichuan University and used for industry applications. The dependence of plasma density and electron temperature on radio frequency power, neutral gas pressure, and different microwave windows was measured by a Langmuir probe on this ion source.

Electron cyclotron resonance (ECR) ion sources are an essential component of heavy-ion accelerators. Over the past few decades advances in magnet technology and an improved understanding of the ECR ion source plasma physics have led to remarkable performance improvements of ECR ion sources. Currently third generation high field superconducting ECR ion sources operating at frequencies around 28 GHz are the state of the art ion injectors and several devices are either under commissioning or under design around the world. At the same time, the demand for increased intensities of highly charged heavy ions continues to grow, which makes the development of even higher performance ECR ion sources a necessity. To extend ECR ion sources to frequencies well above 28 GHz, new magnet technology will be needed in order to operate at higher field and force levels. The superconducting magnet program at LBNL has been developing high field superconducting magnets for particle accelerators based on Nb(3)Sn superconducting technology for several years. At the moment, Nb(3)Sn is the only practical conductor capable of operating at the 15 T field level in the relevant configurations. Recent design studies have been focused on the possibility of using Nb(3)Sn in the next generation of ECR ion sources. In the past, LBNL has worked on the VENUS ECR, a 28 GHz source with solenoids and a sextupole made with NbTi operating at fields of 6-7 T. VENUS has now been operating since 2004. We present in this paper the design of a Nb(3)Sn ECR ion source optimized to operate at an rf frequency of 56 GHz with conductor peak fields of 13-15 T. Because of the brittleness and strain sensitivity of Nb(3)Sn, particular care is required in the design of the magnet support structure, which must be capable of providing support to the coils without overstressing the conductor. In this paper, we present the main features of the support structure, featuring an external aluminum shell pretensioned with water-pressurized bladders, and we analyze the expected coil stresses with a two-dimensional finite element mechanical model.

Electron cyclotron resonance (ECR) ion sources are used for cyclotron complex and atomic physics research at the Institute of Modern Physics (IMP). Intense beams of highly charged gaseous and metallic ions could be produced by the IMP 14.5 GHz ECR ion source (LECR2-Lanzhou Electron Cyclotron Resonance Ion Source No. 2). A particular emphasis has been put on the production of metallic ion beams recently. Metallic ion beams of Mg, Ca, Fe, Ni, Cu, Zn, and Pb were tested at the IMP 14.5 GHz ECR ion source (LECR2) to improve beam intensities and long-term stability. A new ECR ion source (Lanzhou Electron Cyclotron Resonance Ion Source No. 3), an upgraded version of the IMP 14.5 GHz ECR (LECR2) but with double-frequency wave heating (10 GHz+14.5 GHz), is under commissioning. The preliminary results of this new source will be presented. To satisfy the requirements of the heavy ion cooling storage ring that is under construction at IMP, a fully superconducting ECR ion source (Lanzhou Electron Cyclotron Resonance Ion Source with Superconducting Coils) with a completely new structure is being developed for the production of intense heavy ion beams of very high charge states, such as Xe30+ and U40+. The superconducting magnet consists of three axial solenoid coils and six saddle-curved sextupole coils with a cold iron structure as field booster and clamp. At full excitation, this magnet assembly will produce maximum peak fields on axis of 4.0 T at the injection, 2.2 T at the extraction region, and a radial sextupole field of 2.0 T at plasma chamber wall. The design features and status of this new superconducting ECR ion source will be presented.

Summary form only given. Electron Cyclotron Resonance (ECR) ion sources produce high charge state, intense heavy-ion beams for many high energy and nuclear physics accelerators. Several third generation sources utilizing superconducting magnet structures and gyrotrons operating at frequencies greater than 20 GHz are now in operation. Recent results from the LBNL 28 GHz ECR ion source VENUS include 3000 eμA of O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6+</sup> and more than 400 eμA of U <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33+</sup> . New accelerators under design will require even more intense beams and designs for a next generation ECR ion source are being developed. Many years ago, R. Geller predicted that the current of ECR ion sources should scaled as the square of the RF frequency when the magnetic confinement fields are scaled linearly with the frequency [Geller, R., et al., 1987] and this has been shown to hold up to at least 28 GHz. To meet the requirements of the new facilities, next generation ECR ion sources are being designed to operate at roughly 50 GHz with axial magnetic fields up to 7 T and radial fields up to 4 T. This will require advanced magnet structures, perhaps utilizing Nb3Sn and new coil geometries. [Lyneis, C., et al., 2011] In addition, to couple the short wavelength, high power microwaves into the ECR plasma may require conversion of the gyrotron power to HE11 or gaussian TEM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">000</sub> waves prior to being launched into the plasma. In this paper the operation of third generation ECR ion sources and the concepts and challenges for a next generation ECR source will be discussed.

The electron cyclotron resonance (ECR) ion source is special type hot plasma machine where the high temperature electrons co-exist with multiply charge state ions and neutrals. A few years ago 6.4 GHz. ECR ion source (VEC-ECR) was developed indigenously at VECC. This multiply charged ion source is being used continuously to inject heavy ion beams into the cyclotron. Vacuum plays the major role in ECR ion source. The water cooled plasma chamber is made from an oxygen free high conductivity copper billet to meet the suitable surface condition for vacuum purpose. The entire volume of the ion source is pumped by two 900 1/s special type oil diffusion pumps to achieve 5×10−8 Torr. Usually main plasma chamber is pumped by the plasma itself. Moreover a few 1/s additional pumping speed is provided through extraction hole and pumping slot on the extraction electrode. A study has been carried out to understand the role of vacuum on the multiply charged heavy ion production process. Considering the ion production and loss criteria, it is seen that for getting Ar18+ better vacuum is essential for lower frequency operation. So, an ECR ion source can give better charge state current output operating at higher frequency and stronger confining magnetic field under a specific vacuum condition. The low pressure condition is essential to minimize charge exchange loss due to recombination of multiply charged ions with the neutral atoms. A fixed ratio of neutral to electron density must be maintained for optimizing a particular charge state in the steady state condition. As the electron density is proportional to square of the injected microwave frequency (ne∝f2) a particular operating pressure is essential for a specific charge state. From the study, it has been obtained that the production of Ar18+ ions needs a pressure ∼ 9.6×10−8 Torr for 6.4 GHz. ECR ion source. It is also obtained that an ECR ion source, works at a particular vacuum level, can give better charge state production performance, if it operates at higher frequency and stronger magnetic confinement.

Ion source development over the last 20 years at the IMP is reviewed. For versatile purposes, several types of ion sources have been involved in the research and development work at the IMP, i.e., the highly charged ECR (Electron Cyclotron Resonance) ion source, intense microwave ion source or the 2.45 GHz intense beam ECR ion source, and laser ion source (LIS). In the development of ECR ion sources, SECRAL (Superconducting ECR ion source with Advanced design in Lanzhou), Lanzhou ECR ion source, and Lanzhou all permanent magnet ECR ion source series have been made, which can cover the operation microwave frequency range of 10-28 GHz. The LIS with an Nd:YAG laser with a maximum output energy of 8 J in 8 ns pulse duration has been developed for very intense short pulse ion beams from solid materials such as C, Ti, Ni, Ag, and so on. Microwave ion sources have been built to produce intense pulsed or direct current beams from several mA to 100 mA for either high intensity accelerators or applications. This paper will give an overview of the high intensity ion source development at the IMP, especially on the recent progress and new results, such as the status of the fourth generation ECR ion source (first fourth generation ECR ion source), the production of recorded highly charged ion beams with SECRAL sources, key technology research studies, and so on.

The number density of electrons, the energy (electron temperature), and energy distribution are three of the fundamental properties which govern the performance of electron cyclotron resonance (ECR) ion sources in terms of their capability to produce high charge state ions. The maximum electron energy is affected by several processes including the ability of the plasma to absorb power. In principle, the performances of an ECR ion source can be realized by increasing the physical size of the ECR zone in relation to the total plasma volume. The ECR zones can be increased either in the spatial or frequency domains in any ECR ion source based on B-minimum plasma confinement principles. The former technique requires the design of a carefully tailored magnetic field geometry so that the central region of the plasma volume is a large, uniformly distributed plasma volume which surrounds the axis of symmetry, as proposed in Ref. . Present art forms of the ECR source utilize single frequency microwave power supplies to maintain the plasma discharge; because the magnetic field distribution continually changes in this source design, the ECR zones are relegated to thin ‘‘surfaces’’ which surround the axis of symmetry. As a consequence of the small ECR zone in relation to the total plasma volume, the probability for stochastic heating of the electrons is quite low, thereby compromising the source performance. This handicap can be overcome by use of broadband, multiple frequency microwave power as evidenced by the enhanced performances of the CAPRICE and AECR ion sources when two frequency microwave power was utilized. We have used particle-in-cell codes to simulate the magnetic field distributions in these sources and to demonstrate the advantages of using multiple, discrete frequencies over single frequencies to power conventional ECR ion sources. The electron heating rates are found to scale directly in proportion to the resonant plasma ‘‘volume.’’

We are constructing a tandem type electron cyclotron resonance (ECR) ion source (ECRIS). The first stage of this ECRIS has a large-bore with cylindrically comb-shaped permanent magnets. 2.45GHz and 11-13GHz microwaves can be supplied individually and simultaneously to the plasma chamber. For 2.45GHz, a coaxial semi-dipole antenna is used to feed the microwaves. In previous experiments, there were two problems encountered when running the 2.45GHz microwaves. High incident power was necessary to keep ECR discharge at low operating pressure because of high reflected microwave power. The surface of a support insulator between the inner and the outer electrodes of coaxial semi-dipole antenna was easily metalized by sputtering of the metal wall inside the chamber. The purpose of this study was to solve these problems. Performing several simulation experiments supports the hypothesis that the position of the support insulator is significant for microwave power efficiency. The end result was the ability to sustain ECR discharges at extremely low incident microwave power, several tens of watts, by optimized matching of the position and shape of the insulator.

The next-generation heavy ion beam accelerators such as the proposed Rare Isotope Accelerator (RIA), the Radioactive Ion Beam Factory at RIKEN, the GSI upgrade project, the LHC-upgrade, and IMP in Lanzhou require a great variety of high charge state ion beams with a magnitude higher beam intensity than currently achievable. High performance Electron Cyclotron Resonance (ECR) ion sources can provide the flexibility since they can routinely produce beams from hydrogen to uranium. Over the last three decades, ECR ion sources have continued improving the available ion beam intensities by increasing the magnetic fields and ECR heating frequencies to enhance the confinement and the plasma density. With advances in superconducting magnet technology, a new generation of high field superconducting sources is now emerging. They are designed to meet the requirements of these next generation accelerator projects. The paper will briefly review the field of high performance ECR ion sources and the latest developments for high intensity ion beam production. The currently most advanced next-generation superconducting ECR ion source VENUS will be described in more detail.

The spectral temperature $T_{s}$ obtained from bremsstrahlung spectra emitted from electron cyclotron resonance (ECR) ion sources (ECRISs), in which the plasma is confined in a minimum-B magnetic field, is used as a relative indication of the temperature of the plasma hot electrons. Past bremsstrahlung measurements taken on ECRISs indicate that $T_{s}$ is strongly dependent on the magnetic field gradient at the resonance zone or $({B_{\mathrm{ min}}}/{B_{\mathrm{ ECR}}})$ . However, this dependence was never fully proven or explained. To further our understanding a more detailed study of the bremsstrahlung radiation for X-rays above 10 keV is underway using VENUS, a third-generation ECRIS at Lawrence Berkeley National Laboratory. Initial analysis of previous and new data has revealed that $T_{s}$ appears to be dependent solely on the minimum magnetic field $B_{\mathrm{ min}}$ rather than $({B_{\mathrm{ min}}}/{B_{\mathrm{ ECR}}})$ and the microwave frequency $\omega$ . Decoupling $T_{s}$ from $({B_{\mathrm{ min}}}/{B_{\mathrm{ ECR}}})$ , mainly $B_{\mathrm{ ECR}}$ , implies that $T_{s}$ does not depend on the magnitude of the heating frequency $\omega$ . While it certainly appears to be true that plasma density $n_{e}(\propto \omega ^{2}\propto B^{2})$ increases with heating frequency, as was postulated by Geller in 1987, a more careful consideration into the heating mechanism of the plasma electrons is warranted. The disassociation of $T_{s}$ from the heating frequency $\omega$ , while an interesting discovery, implies that we must change the way we understand how ECRISs operate. This paper presents new bremsstrahlung measurements, analyses, and discussions of the results.

The effect of magnetic field strength on the time evolution of high energy bremsstrahlung radiation created by an electron cyclotron resonance ion source

The electron cyclotron resonance coupled to a laser ion source for charge state enhancement method, based on the coupling of a laser ion source with an electron cyclotron resonance (ECR) ion source in order to produce highly charged ions of metallic elements, demonstrated its validity some years ago, although some aspects remained unclear, in particular the optimization of the ion capture probability through ion–ion scattering. Another crucial item that determines the efficiency of the coupling is the variation of the energy content of the electron cyclotron resonance ion source (ECRIS) plasma: when the ions produced by means of the laser ablation are captured, they deposit a great amount of energy into the magnetically confined plasma. The released energy perturbs the ECR plasma, thus increasing the losses onto the chamber walls and the emittance of the extracted beam. Only a rough estimation of the energy content perturbations has been available up to now, so Monte Carlo simulations have been used to improve the description of the ion capture mechanism and the energy perturbation. The real magnetic field structure of ECRIS and a realistic plasma density distribution have been taken into account, as the code considers the ECR plasma properties emerging from particle in cell (PIC) simulations and from experimental measurements that permit one to determine locally the energy perturbation. The effects of electric fields on the ion stream coming from the laser-ablated target have been also considered, resulting in better coupling after the ion energy decrease.