ELECTRON CYCLOTRON RESONANCE ION SOURCES: 16th International Workshop on ECR Ion Sources ECRIS'04
749(2005); http://dx.doi.org/10.1063/1.1893356View Description Hide Description
VENUS (Versatile ECR ion source for NUclear Science) is a next generation superconducting ECR ion source, designed to produce high current, high charge state ions for the 88‐Inch Cyclotron at the Lawrence Berkeley National Laboratory. VENUS also serves as the prototype ion source for the RIA (Rare Isotope Accelerator) front end. The magnetic confinement configuration consists of three superconducting axial coils and six superconducting radial coils in a sextupole configuration. The nominal design fields of the axial magnets are 4T at injection and 3T at extraction; the nominal radial design field strength at the plasma chamber wall is 2T, making VENUS the world most powerful ECR plasma confinement structure. From the beginning, VENUS has been designed for optimum operation at 28 GHz with high power (10 kW).
In 2003 the VENUS ECR ion source was commissioned at 18 GHz, while preparations for 28 GHz operation were being conducted. During this commissioning phase with 18 GHz, tests with various gases and metals have been performed with up to 2000 W RF power. At the initial commissioning tests at 18 GHz, 1100 eμA of O6+, 160 eμA of Xe20+, 160 eμA of Bi25+ and 100 eμA of Bi30+ and 11 eμA of Bi41+ were produced.
In May 2004 the 28 GHz microwave power has been coupled into the VENUS ECR ion source. At initial operation more than 320 eμA of Xe20+ (twice the amount extracted at 18 GHz), 240 eμA of Bi24+ and Bi25+, and 245 eμA of Bi29+ were extracted. The paper briefly describes the design of the VENUS source, the 28 GHz microwave system and its beam analyzing system. First results at 28 GHz including emittance measurements are presented.
749(2005); http://dx.doi.org/10.1063/1.1893357View Description Hide Description
Great efforts have been made to develop highly charged ECR ion sources for application of heavy ion accelerator and atomic physics research at IMP in the past few years. The latest development of ECR ion sources at IMP is briefly reviewed. Intense beams with high and intermediate charge states have been produced from IMP LECR3 by optimization of the ion source conditions including rf frequency extended up to 18GHz. 1.1 emA of Ar8+ and 325 eμ A of Ar11+ were produced. Dependence of beam emittance on those key parameters of ECR ion source, beam extraction and space charge compensation were experimentally studied at LECR3. Furthermore, an advanced superconducting ECR ion source named SECRAL is being constructed. SECRAL is designed to operate at rf frequency 18–28GHz with axial mirror magnetic fields 3.6–4.0 Tesla at injection, 2.2 Tesla at extraction and sextupole field 2.0 Tesla at the wall. The superconducting magnet with sextupole and three solenoids was tested in a test‐cryostat and 95% of designed fields were reached. Construction status and planed schedule of SECRAL are presented.
Production of Highly Charged Heavy Ions by means of a Hybrid Source in Dc mode and in Afterglow Mode749(2005); http://dx.doi.org/10.1063/1.1893358View Description Hide Description
The ECLISSE experiment has been carried out by coupling a Laser Ion Source (based on a Nd:YAG laser (0.9 J / 9 ns, laser power densities <1011 W/cm2) to the SERSE superconducting ECR ion source. Cw beams of highly charged ions from metal samples without the use of ovens or sputtering technics were obtained in a variety of experimental conditions. The maximum charge states obtained from the ECRIS were 38+ for Ta and 41+ for Au. The peak current was obtained for 25+ and 29+ respectively and it was in the order of some tens of μA. In this work the analysis of some preliminary results obtained in afterglow mode will be also presented. We employed microwave pulse (length 4 msec) and laser pulse (length 9 nsec) with the same frequency (30 Hz) and variable relative phase. For appropriate phase values, a current enhancement of about one order of magnitude was observed.
749(2005); http://dx.doi.org/10.1063/1.1893359View Description Hide Description
The first High Temperature Superconducting Electron Cyclotron Resonance Ion Source (HTS‐ECRIS) called PKDELIS has been developed as a collaborative project. The source has been designed for suitable use on a high voltage platform with minimum requirements of electrical power and water cooling. The design is based on the required A/q of ∼ 7 for the High Current Injector (HCI) of the Superconducting Linear Accelerator (SC‐LINAC) at Nuclear Science Centre and to provide relatively higher beam currents of multiply charged ions. High Temperature Superconducting coils (Bi‐2223) have been chosen to reduce the power and cooling requirements for obtaining large axial magnetic fields corresponding to a frequency of 18 GHz. The HTS coils are operated in a superconducting mode in a temperature range of about 20 to 22 K using Gifford‐McMahon type cryo‐refrigerators. A 36 element hexapole was designed using NdFeB to obtain higher fields at the chamber wall. The source is tested thoroughly by producing beams of carbon, oxygen, neon, argon, xenon, tantalum and lead at various charge states having analysed current up to 2 mA. The detailed design aspects and test results are presented.
749(2005); http://dx.doi.org/10.1063/1.1893360View Description Hide Description
Beam intensities of medium charge‐state Ar, Kr and Xe ions have been measured under the various conditions. Beam intensities were strongly dependent on the plasma electrode position and Bmin. By optimizing these parameters, 2 mA of Ar8+, 0.6 mA of Kr13+, and 0.3 mA of Xe18,20+ were obtained. We observed that the RF power of 100∼150W was enough to produce 1mA of Ar8+ form RIKEN 18 GHz ECRIS by optimizing these parameters.
749(2005); http://dx.doi.org/10.1063/1.1893361View Description Hide Description
The main focus of the JYFL (University of Jyväskylä, Department of Physics) ion source group has recently been on the development of a new plasma chamber and measurements of the plasma potential with a device developed at JYFL. The new plasma chamber is based on an idea described at ICIS’03 in Dubna. The work is mainly presented elsewhere in these proceedings (P. Suominen et al.). The plasma potential measurements are based on the use of a decelerating voltage. With the aid of the device, information about the plasma potential and the temperature of the ions can be obtained. This work is also described elsewhere in these proceedings (O. Tarvainen). The radial feeding of the microwave power into the plasma chamber has been studied. According to the first results approximately the same intensity can be reached if the microwave power is launched into the plasma chamber axially or through the radial port. The phenomena will be investigated in more detail. Development work for the production of metal ion beams has also been carried out. An overview of the work of the JYFL ion source group will be presented.
749(2005); http://dx.doi.org/10.1063/1.1893362View Description Hide Description
The usefulness of two‐frequency heating for the production of high‐charge state high‐intensity beams from an ECRIS has been well established. Factors of 2→5 increase in beam currents have been observed accompanied by a shift to higher charge states. The ECRIS at Argonne National Laboratory has been routinely operated utilizing a 14 GHz klystron and a tunable 11–13 GHz traveling wave tube amplifier (TWTA) and the operating characteristics of the source are well known. However, the characteristics of the multi‐frequency heated plasma are less well known. Investigations regarding the changes in the source production have been taking place at Argonne National Laboratory. Parameters such as the charge state distribution (CSD), production times and plasma potential have been measured for a multi‐frequency heated plasma with emphasis being given to the effect of the frequency gap between the two RF waves. It has been found that the production times decrease in multi‐frequency mode with a corresponding increase in the CSD and the overall beam output. At the same time, the plasma potential appears to not change significantly. It has also been found that a larger frequency gap (14.0 and 10.84 GHz), while producing higher charge‐state ions, produces less overall beam of the material of interest but reaches equilibrium more quickly when compared to a smaller gap (14,0 and 12.31 GHz). Possible mechanisms for the observed behavior will be discussed.
749(2005); http://dx.doi.org/10.1063/1.1893363View Description Hide Description
Recent ECRIS development at KVI is motivated by a new experimental program, called TRIμP, that aims to study fundamental symmetries and interactions by very precise measurements of decaying short‐lived radioactive nuclides trapped in ion or atom traps. ECRIS produced heavy‐ion beams are accelerated by the AGOR cyclotron and used as driver beams to produce the short‐lived radionuclei of interest. This new experimental program puts new demands on the injector ECRIS, i.e. a variety of metal‐ion beams and a significant intensity upgrade up to two‐orders of magnitude. This report briefly summarizes what has been achieved up to now and what will be done in the near future to meet the challenges.
749(2005); http://dx.doi.org/10.1063/1.1893364View Description Hide Description
749(2005); http://dx.doi.org/10.1063/1.1893365View Description Hide Description
Compared to the simulation of classical high perveance extraction systems for high current ion sources, the extraction of typical ECRIS is more complicated because more parameters, partially unknown, are involved. To reduce the computational effort, it would be helpful to determine several of these unknown parameters affecting mainly the starting conditions for trajectories in space and in momentum. The influence of the magnetic field on the beam in the extraction region is studied. Here the magnetic flux density distribution is fixed, but the starting conditions of all particles can be modified within reasonable limits in the simulation to investigate this influence.
The GSI CAPRICE ECRIS was equipped with a movable accel‐decel extraction system in order to investigate the influence of electric field gradient and space charge compensation as well as further effects of ion extraction. First results will be presented and will be compared with computer simulations. For the most simple case of Helium operation, simulation shows good agreement with experimental results, indicating the correctness of the applied model.
749(2005); http://dx.doi.org/10.1063/1.1893366View Description Hide Description
The Warp code, developed for heavy‐ion driven inertial fusion energy studies, is used to model high intensity ion (and electron) beams. Significant capability has been incorporated in Warp, allowing nearly all sections of an accelerator to be modeled, beginning with the source. Warp has as its core an explicit, three‐dimensional, particle‐in‐cell model. Alongside this is a rich set of tools for describing the applied fields of the accelerator lattice, and embedded conducting surfaces (which are captured at sub‐grid resolution). Also incorporated are models with reduced dimensionality: an axisymmetric model and a transverse “slice” model. The code takes advantage of modern programming techniques, including object orientation, parallelism, and scripting (via Python). It is at the forefront in the use of the computational technique of adaptive mesh refinement, which has been particularly successful in the area of diode and injector modeling, both steady‐state and time‐dependent. In the presentation, some of the major aspects of Warp will be overviewed, especially those that could be useful in modeling ECR sources. Warp has been benchmarked against both theory and experiment. Recent results will be presented showing good agreement of Warp with experimental results from the STS500 injector test stand. Additional information can be found on the web page http://hif.lbl.gov/theory/WARP_summary.html.
749(2005); http://dx.doi.org/10.1063/1.1893367View Description Hide Description
An efficient and fast instrument to measure the plasma potential of ECR ion sources (ECRIS) has been developed at the Department of Physics, University of Jyväskylä (JYFL). The operating principle of the instrument is to measure the energy of the ion beam by applying a decelerating voltage to a mesh located in the beam line after mass analysis. The plasma potential is determined by measuring the current at the grounded electrode situated behind the mesh as a function of this adjustable voltage. The measurements were performed with ECR ion sources at JYFL (6.4 and 14 GHz) and at Argonne National Laboratory (14 GHz). The plasma potential was measured as a function of different source parameters such as microwave power, gas feed rate (with different gases), voltage of the biased disk and magnetic field strength. The effects of gas mixing and double‐frequency heating were also studied. The energy of the ions extracted from an ECRIS plasma comes from the source potential, plasma potential and the thermal energy of the ions. In order to distinguish the effect of the ion temperature on the measured curve simple computer simulations were performed. With the aid of the simulation and assuming a certain potential profile and Maxwellian velocity (energy) distribution of the ions, it was seen that the ion temperature should affect the shape of the measured curve in the region where the adjustable deceleration voltage is close to the value of the plasma potential. In the measurements it was observed that the shape of the curve in this region changed dramatically when gas mixing was used. However, the effect was typical only for low charge states of the heavier element while the curves measured with higher charge states remained almost unchanged. The effect of gas mixing on the ion temperature will be discussed based upon the obtained results.
749(2005); http://dx.doi.org/10.1063/1.1893368View Description Hide Description
The 14.5 GHz ECR ion source of the ATOMKI is a stand‐alone device producing highly charged ion beams for ion‐surface experiments and a variety of low charged plasmas and beams for plasma physics studies and for practical applications. In the past two years we performed plasma diagnostics measurements using Langmuir‐probes and X‐ray camera. Langmuir‐probe results allowed estimating the plasma potential close to the resonance zone. The studying of X‐ray pictures of Xe‐Ar plasmas helps understanding the gas‐mixing phenomena. A mixture plasma of fullerene and ferrocene was generated and FeC60 hybrid molecules were detected in the extracted beam.
Effect of the plasma electrode position on the beam intensity and emittance of the RIKEN 18 GHz ECRIS749(2005); http://dx.doi.org/10.1063/1.1893369View Description Hide Description
We measured the beam intensity of Ar, Kr and Xe ions as a function of plasma electrode position. The beam intensities of lower charge state heavy ions increased when moving the plasma electrode toward the ECR zone. The RF power absorbed in the plasma chamber was slightly dependent on the gas pressure and 70% of injected RF power was absorbed. The emittance of ion source was gradually increased with increasing the drain current, which may be due to the space charge effect.
749(2005); http://dx.doi.org/10.1063/1.1893370View Description Hide Description
A proposed upgrade to the radioactive beam capability of the ATLAS facility has been proposed using 252Cf fission fragments thermalized and collected into a low‐energy particle beam using a helium gas catcher. In order to reaccelerate these beams the ATLAS ECR‐I will be reconfigured as a charge breeder source. A 1Ci 252Cf source is expected to provide sufficient yield to deliver beams of up to ∼103 far from stability ions per second on target. A brief facility description and the expected performance information are provided in this report.
749(2005); http://dx.doi.org/10.1063/1.1893371View Description Hide Description
We present new results on the X‐ray spectroscopy of multicharged argon, sulfur and chlorine obtained with the Electron Cyclotron Resonance Ion Trap (ECRIT) in operation at the Paul Scherrer Institut (Villigen, Switzerland). We used a Johann‐type Bragg spectrometer with a spherically‐bent crystal, with an energy resolution of about 0.4 eV. The ECRIT itself is of a hybrid type, with a superconducting split coil magnet, special iron inserts which provides the mirror field, and a permanent magnetic hexapole. The high frequency was provided by a 6.4 GHz microwave emitter.
We obtained high intensity X‐ray spectra of multicharged F‐like to He‐like argon, sulfur and chlorine with one 1s hole. In particular, we observed the 1s2s 3 S 1 → 1s 2 1 S 0 M1 and 1s2p 3 P 2 → 1s 2 1S 0 M2 transitions in He‐like argon, sulfur and chlorine with unprecedented statistics and resolution. The energies of the observed lines are being determined with good accuracy using the He‐like M1 line as a reference.
We surveyed the He‐like M1 transition intensity as a function of the ECRIT working conditions. In particular we observed the M1 intensity dependency on the coil current and on the injected microwave power.
Novel Technique for Trace Element Analysis using the ECRIS and Heavy Ion Linear Accelerator (ECRIS‐AMS)749(2005); http://dx.doi.org/10.1063/1.1893372View Description Hide Description
We have developed the new analytical system which consists of electron cyclotron resonance ion source (ECRIS) and heavy ion linear accelerator. ECRIS‐AMS (Accelerator Mass Spectrometry using Electron Cyclotron Resonance Ion Source) has several advantages described below. 1) The production of positive ions in the ECRIS is not influenced by ionization selectivity. 2) We can analyze many trace elements simultaneously in the material with very low background. 3) We can minimize the spectroscopic interference by using the high temperature ECR plasma. Using this system, we have measured elemental compositions in rock reference samples (JB‐2). From our experimental results, it is considered that the further development and establishment of this method will play an important role in the trace element analysis. For this application, we just need small heavy ion linear accelerator which has acceleration energy of ∼ 1MeV/u. In this contribution, we will present the procedure of analysis in detail and several experimental results for trace element analysis in the materials.
749(2005); http://dx.doi.org/10.1063/1.1893373View Description Hide Description
Photoionization of multiply charged ions is studied using the merged‐beams technique at the Advanced Light Source. An ion beam is created using a compact 10‐GHz all‐permanent‐magnet ECR ion source and is accelerated with a small accelerator. The ion beam is merged with a photon beam from an undulator to allow interaction over an extended path. Absolute photoionization cross sections have been measured for a variety of ions along both isoelectronic and isonuclear sequences.
Formation of Electron Distribution Function in ECR Discharge Sustained by Strong Microwave Emission in an Open Trap749(2005); http://dx.doi.org/10.1063/1.1893374View Description Hide Description
We consider a formation of Electron Distribution Function (EDF) in the Electron Cyclotron Resonance (ECR) discharge in an open trap. The ECR heating by strong microwaves, ionization, collisions and ambipolar losses are considered. The model is based on a system of two‐dimensional Fokker‐Plank equation for EDF. The stationary solution for EDF is investigated analytically. It consists of three groups of electrons: hot electrons with highly anisotropic velocity distribution that are heated in the ECR region, cold electrons with isotropic distribution that define the losses from the trap and warm electrons with considerably anisotropic distribution that are concentrated in the center of the trap and do not reach the ECR region. We build a qualitative model for the electron distribution function such that the original differential equation for EDF is transformed into two algebraic equations with two unknown parameters: neutral density and main plasma density. The latter can be solved analytically. The applicability of these results to a self‐consistent model for ECR ion source is discussed. We show that the solution contradicts experimental results so that important effect is not taken into account in the model.