ECR Charge Breeder Research Articles

Radioactive ion-beam development at SPIRAL1

SPIRAL1 at GANIL is a facility dedicated to the production of radioactive ion beams (RIBs) and their post-acceleration. A major upgrade allowed this facility to produce RIBs of condensable elements. It does so by using both a hot 1+ ion source and an ECR Charge Breeder where the latter is used to increase the ion charge state for post-acceleration. The SPIRAL1 team is pursuing R&D on both fronts in order to expand the offer of RIBs. Several 1+ sources have been or will be tested in 2023: (1) MonoNaKe, a surface ion source, is being modified to ionize short-lived lithium isotopes (2) TULIP, dedicated to ionize short lived fusion-evaporation residues has been tested online for the second time (3) the FEBIAD source has produced radioactive Cr ions for the first time. The SPIRAL1 Charge Breeder (SP1CB) is now fitted with a fixed frequency amplifier (Klystron) and a variable frequency amplifier (travelling wave tube). Using one amplifier, the other, or both, enables several heating modes, giving better control on the charge state distribution at the output of SP1CB.

Latest improvements of the SPIRAL1 facility at GANIL

Since 2001, the SPIRAL1 facility has been providing post-accelerated radioactive beams by the ISOL method. Over the last decade, SPIRAL1 has been improved to provide beams of condensable elements, by using a combination of a FEBIAD-type ion source (to produce 1+ ions) and a PHOENIX ECR charge breeder (to transform 1+ ions into N+ ions for post-acceleration). Both these elements have been improved in recent years: the FEBIAD source has been upgraded to improve its efficiency and reliability over time and the charge breeder was modified to extend the range of available charge states. In addition, a krypton beam was recently sent in a FEBIAD target ion-source system (TISS), allowing to produce medium mass radioactive 1+ ions that had not been previously produced in SPIRAL1. This papers compiles recent results illustrating the gain in performances and beam offer at SPIRAL1.

Recent developments and results of the LPSC PHOENIX type ECR charge breeder

Four models of the PHOENIX ECR charge breeder have been manufactured for ISOL application. Two are currently under operation at TRIUMF (ISAC) and GANIL (SPIRAL 1) while the SPES one is being installed on the facility. The last model is set on the LPSC 1+N+ test bench where a R&D program is ongoing to improve its performances. The last modifications consisted in improving the beam line vacuum and the alignment. Commissioning experiments showed an improvement of the charge breeder performances for all the tested species. The global CB efficiency is close to 100% for Cs when correcting the measurements with the beam transmission. Na and K efficiencies have increased significantly to reach 18.7% for Na8+ and 22.7% for K9+. In parallel, the charge breeder plasma was studied injecting short pulses of 1+ ions and using a zero-dimension model to estimate the plasma parameters. These experiments have provided a better understanding of the performance improvement. The last developments of the LPSC Charge Breeder together with the experimental results are presented.

Progress in the design and construction of SPES at INFN-LNL

INFN-LNL is constructing an ISOL (Isotope Separation On Line) facility delivering neutron rich ion beams at 10AMeV or beyond, making use of the linear accelerator ALPI as the secondary accelerator. The facility includes a direct ISOL target based on UCx and able to reach 1013fissions/s. In parallel, an applied physics facility will be developed, with applications in medicine and neutron production. The SPES project is a national facility, approved and funded. Commissioning with the first exotic species is expected in 2019. The primary accelerator is a commercial cyclotron, which will send a 40MeV, 200μA proton beam onto an UCx target, connected to SIS, PIS and LIS ion sources. The extracted beam is purified through a Low Resolution Mass Separator (LMRS, i.e. a Wien filter and a dispersive dipole), a beam cooler and a High Resolution Mass Separator (HRMS) and sent to an ECR charge breeder to boost the exotic beam charge state. The highly charged exotic beam is further separated in a MRMS (Medium Resolution Mass Separator) and injected into a 100% duty cycle RFQ and into the existing superconducting linac ALPI, which will be refurbished and upgraded to be an efficient exotic beam accelerator. The upgrade of ALPI will give ∼10AMeV energy to 132Sn19+, taken as the reference ion beam. The paper presents the status of the design and construction of the SPES facility.

Off-line commissioning of EBIS and plans for its integration into ATLAS and CARIBU.

An Electron Beam Ion Source Charge Breeder (EBIS-CB) has been developed at Argonne to breed radioactive beams from the CAlifornium Rare Isotope Breeder Upgrade (CARIBU) facility at Argonne Tandem Linac Accelerator System (ATLAS). The EBIS-CB will replace the existing ECR charge breeder to increase the intensity and significantly improve the purity of reaccelerated radioactive ion beams. The CARIBU EBIS-CB has been successfully commissioned offline with an external singly charged cesium ion source. The performance of the EBIS fully meets the specifications to breed rare isotope beams delivered from CARIBU. The EBIS is being relocated and integrated into ATLAS and CARIBU. A long electrostatic beam transport system including two 180° bends in the vertical plane has been designed. The commissioning of the EBIS and the beam transport system in their permanent location will start at the end of this year.

The new ECR charge breeder for the Selective Production of Exotic Species project at INFN—Laboratori Nazionali di Legnaro

The Selective Production of Exotic Species (SPES) project is an ISOL facility under construction at Istituto Nazionale di Fisica Nucleare-Laboratori Nationali di Legnaro (INFN-LNL). 1+ radioactive ions, produced and extracted from the target-ion-source system, will be charge bred to high charge states by an ECR charge breeder (SPES-CB): the project will adopt an upgraded version of the PHOENIX charge breeder, developed since about twenty years by the Laboratoire de Physique Subatomique et de Cosmologie (LPSC). The collaboration between LNL and LPSC started in 2010 with charge breeding experiments performed on the LPSC test bench and led, in June 2014, to the signature of a Research Collaboration Agreement for the delivery of a complete charge breeder and ancillaries, satisfying the SPES requirements. Important technological aspects were tackled during the construction phase, as, for example, beam purity issues, electrodes alignment, and vacuum sealing. This phase was completed in spring 2015, after which the qualification tests were carried out at LPSC on the 1+/q+ test stand. This paper describes the characteristics of the SPES-CB, with particular emphasis on the results obtained during the qualification tests: charge breeding of Ar, Xe, Rb, and Cs satisfied the SPES requirements for different intensities of the injected 1+ beam, showing very good performances, some of which are "best ever" for this device.

CARIBU: a new facility for the study of neutron-rich isotopes

The Californium Rare Ion Breeder Upgrade (CARIBU) to the ATLAS superconducting linac facility is currently being commissioned. It provides low-energy and re-accelerated beams of neutron-rich isotopes obtained from 252Cf fission. The fission products from a 252Cf source are stopped in a large high-intensity gas catcher, thermalized and extracted through an RFQ cooler, accelerated to 50 kV and mass separated in a high-resolution separator before being sent to either an ECR charge breeder for post-acceleration through the ATLAS linac or to a low-energy experimental area. This approach gives access to beams of very neutron-rich isotopes, many of which have not been available at low or Coulomb barrier energies previously. These beams provide unique opportunities for measurements along the r-process path. To take advantage of these unique possibility, the reaccelerated beams from CARIBU will be made available at the experimental stations of ATLAS to serve equipment such as Gammasphere, HELIOS and the reaction spectrometers. In addition, the Canadian Penning Trap (CPT) mass spectrometer has been moved to the CARIBU low-energy experimental area and a new injection line has been built. The new injection line consists of a RFQ buncher sitting on a 50 kV high-voltage platform that will accumulate the mass separated 50 kV radioactive beams, cool and extract them as a pulsed beam of 3 keV. This beam can be sent either to a tape station for diagnostics and tuning, or a cryogenic linear trap for preparation before transfer to the high-precision Penning trap where the mass measurements will take place. Initial CARIBU commissioning is proceeding with a 2 mCi source that will be replaced by a 100 mCi source as the commissioning proceeds. Final operation will use a 1 Ci source and attain yield in excess of 107 ions/sec for the most intense beams at low energy, an order of magnitude less for reaccelerated beams.

KEKCB-18 GHz ECR charge breeder at TRIAC

The KEKCB is an electron cyclotron resonance ion source (ECRIS) operating at the microwave frequency of 18GHz and has successfully operated as the charge breeder at Tokai Radioactive Ion Accelerator Complex (TRIAC). Following an overview of the TRIAC, the recent operating results of the KEKCB have been demonstrated. Special attention was paid on the element-dependent charge breeding efficiency and the beam impurity originating from the ECR plasma of the KEKCB.

Potentials of the ECR 1+ n+ charge breeding for radioactive ions

During the past three years, a Phoenix ECR charge breeder has been tested on-line with various beams delivered by the ISOLDE facility. The performances obtained so far are compatible with most of the requirements for future production of intense radioactive charge bred beams. However, there are aspects that are could be improved. These concern beam purity, injection efficiency and the capability of raising high charge state in continuous or pulsed mode. We summarize here the results obtained with the present Phoenix ECR charge breeder and a few simple upgrades that are foreseen to improve its performances.

Charge breeding ions for nuclear physics with the PHOENIX ECRIS

At ISOLDE, CERN, an online PHOENIX ECR charge state breeder is being tested for the investigation of the 1+→n+ scenario for the next generation ISOL postaccelerators. As the program of tests reaches an end, the possible physics experiments with multiply charged radioactive ion beams are being investigated. Especially the use of the ECR charge breeder in combination with a high voltage platform would permit an acceleration of the radioactive ions produced at ISOLDE to total energies up to a few MeV. This opens up possibilities for nuclear astrophysics experiments such as various studies of low energy radiative capture reactions. Experiments requiring the implantation of radioactive ions in a substrate at varying depth can also be conceived. This contribution presents the various aspects of the current performances of the PHOENIX ECR charge breeder that could benefit physics applications.

Radioactive beams from 252Cf fission using a gas catcher and an ECR charge breeder at ATLAS

The Californium Rare Ion Breeder Upgrade (CARIBU) for the ATLAS facility is under construction. The facility will use 252Cf fission fragments thermalized and collected into a low-energy particle beam by a helium gas catcher. In order to reaccelerate these beams an existing ATLAS ECR ion source is being reconfigured as a charge breeder source. A 1Ci 252Cf source will provide sufficient yield to deliver beams of up to ∼106 far-from-stability ions per second on target. The facility design, expected performance and the project status will be presented in this paper.

Test results of 18 GHz ECR charge breeder for KEK–JAERI RNB facility

Some of the test results of KEK ECR charge breeder made for KEK–JAERI RNB facility are presented and discussed. The charge breeding efficiencies for singly charged ions of noble gases have been measured; typically 13.5% of Ar9+, 10.4% of Kr12+, and 6.8% of Xe20+ with a global efficiency of about 50%. By injecting pulsed Xe1+ ion beam into the charge breeder, the time necessary for charge breeding has been also measured and found to be about 60 ms for Xe21+ ions. As an effort to reduce the residual gas ions incidentally existing in the plasma chamber of the charge breeder a nonevaporable getter has been tested, and the preliminary results are discussed.

Stopping efficiency of an ECR charge breeder for axially injected ions

We have simulated the trajectories of ions injected into an ECR plasma, by taking into account explicitly the cumulative small angle scattering of charged ions as well as the confinement magnetic field of the ECR source. Assuming homogeneous and uniform plasma in a given volume, the stopping efficiency, defined as a probability that the injected ions are alive in the plasma volume until their initial directional motions become at random, has been extracted and discussed.

ECRIS as ion source and charge breeder

We will recall the main characteristics of ECR ion sources and their very good property of ionization efficiency. We will start with a review of on line use of ECR ion sources for production of mono or multicharged radioactive ions, and then we will specially focus our attention on charge breeding process for multicharged ion production. Initially developed for the PIAFE project from ISN Grenoble, the ECR charge breeder shows that the beam injection of a primary beam inside an ECR ion source is a very general process for beam production. We will review the latest results obtained on the ISN Grenoble test bench for the production of CW or pulsed metallic ion beams with the so called ‘1 +/ n +’ method. New results are given for CW operation where the efficiency is particularly optimized for application to multicharged radioactive ion production (for example, 3.5% for Zn 1+→Zn 9+, 4.2% for Pb 3+→Pb 24+, 5% for Rb 1+→Rb 15+). Different ion sources have been used to study the variation of the efficiency as a function of the energy of the 1 + primary beam. Charge-state distributions are especially measured for Pb and Rb ions. A new mode of operation, the Electron Cyclotron Resonance Ion Trap (ECRIT) breeder/buncher, which permits the trapping and the bunching of the n + ion beam is demonstrated and experimentally verified. This new method shows that it is possible to modify the time structure of the injected beam, just by trapping the ions inside the plasma and reextracting them by using the ‘afterglow pulsed mode’. We will finish by the presentation of the first result obtained with the first especially dedicated ECR booster developed at the ISN and called PHOENIX.