Production of High-Intensity, Highly Charged Ions

In the past three decades, the development of nuclear physics facilities for fundamental and applied science purposes has required an increasing current of multicharged ion beams. Multiple ionization implies the formation of dense and energetic plasmas, which, in turn, requires specific plasma trapping configurations. Two types of ion source have been able to produce very high charge states in a reliable and reproducible way: electron beam ion sources (EBIS) and electron cyclotron resonance ion sources (ECRIS). Multiple ionization is also obtained in laser-generated plasmas (laser ion sources (LIS)), where the high-energy electrons and the extremely high electron density allow step-by-step ionization, but the reproducibility is poor. This chapter discusses the atomic physics background at the basis of the production of highly charged ions and describes the scientific and technological features of the most advanced ion sources. Particular attention is paid to ECRIS and the latest developments, since they now represent the most effective and reliable machines for modern accelerators.Comment: 42 pages, contribution to the CAS-CERN Accelerator School: Ion Sources, Senec, Slovakia, 29 May - 8 June 2012, edited by R. Baile

Comparison of the charge state distributions of electron cyclotron resonance ion sources working in high B mode at different frequencies

The behavior of the two superconducting electron cyclotron resonance ion sources of Michigan State University-National Superconducting Cyclotron Laboratory and of INFN-Laboratori Nazionali del Sud, operating respectively at 6.4 and 14 GHz is compared in this note. The charge state distributions present a similar shape, when both the sources are optimized for the production of high charge state ions. The beam intensity is roughly proportional to the square of the frequency which may be explained by the difference in plasma density

The Italian contribution to the construction of the linac for the European spallation source

AbstractThe European spallation source (ESS) uses a linear accelerator (linac) to deliver the high intensity proton beam to the target station for producing intense beams of neutrons. At the exit of the linac, the proton beam will have 2 GeV energy and 62.5 mA current. The construction of an accelerator with the contribution of different laboratories is not a new concept but so far the laboratories were controlled by the same government (e.g. in USA and Japan) or they delivered components for an intergovernmental institution like CERN. The European Spallation Source is a research facility that gathers 40 active in-kind (IK) contributors from 13 States, even outside the European Union, so its construction is not only a technical and scientific challenge, but also an economic, political and social experiment. The case of the Italian contribution is interesting because of the structure of Italian industrial ecosystem, mostly based on small and medium-sized enterprises (SME), which may be unsuitable for the case of a research infrastructure which construction requires a high level of R&D investments. Conversely, the well-known flexibility of SME to adapt to the requirements have balanced the weakness and the results are satisfactory. Following the overview of the Linac design, the paper will focus on the key issues of the Italian contribution, the state of the project (73% completion up to now) along with the point of view of the ESS management and the lesson learnt; the major outcomes for the economy and society will complete the discussion

Study of charge state enhancement by means of the coupling of a Laser Ion Source to the ECR ion source SERSE

The possibility to produce intense ion beams from solid elements, by using a pulsed Laser ion source as the first stage of the superconducting ECR ion source SERSE is discussed in the following. The Laser ion source may be used to produce negative or positive ions and electrons that are injected into the plasma of SERSE. The design of the experimental setup and the study of the extraction of ions from a target by means of Nd:Yag laser irradiation are briefly described. This Laser ion source will be located in the plasma chamber of the source SERSE, in presence of its magnetic field. A simple evaluation of the charge state enhancement inside the ECR plasma is also presented in the following

Installation of ECR2 at LNS and Preliminary tests

The source ECR2 has been built in 1998 by Pantechnik, according to the design suggested by LNS Ion Source Group. This design entails some improvements with respect to a standard CAPRICE-type source: a) the magnetic field (up to 1.6 T axial, 1.1 T radial) allows to operate the source at 14 GHz in High B mode and at 18 GHz; b) two frequency heating can be used; c) an aluminum made plasma chamber is used in place of the stainless steel one. The main features of ECR2 along with a review of the preliminary tests will be outlined. Typical currents for fully stripped nitrogen are about 25 emA; for the heaviest ions, 1 emA of Kr28+ and 10 emA of Ta27+ have been measured. The installation at LNS has been completed recently and the details will be given

FIRST BEAM FROM THE TRASCO INTENSE PROTON SOURCE (TRIPS) AT INFN-LNS

Abstract The TRASCO intense proton source (TRIPS) has been installed at INFN-LNS THE SOURCE DESIGN The TRASCO Project is a R&D program which goal is the design of an Accelerator Driving System (ADS) for nuclear waste transmutation. The high current cw proton linear accelerator will drive a subcritical system to transmutate nuclear wastes. [1] The accelerator design is shared between different INFN laboratories and the LNS is in charge of the source design and construction. The proton source TRIPS is a high intensity microwave source, which goal is the injection of a minimum proton current of 35 mA in the following RFQ [2], with a rms normalized emittance lower than 0.2π⋅mm⋅mrad for an operating voltage of 80 kV. With respect to other sources for high intensity applications, some new features have been added, according to our experience with the high-intensity source SILHI • the microwave matching system has been improved; • a system to move the coils on-line has been realized; • the extraction system has been optimised with the aim to increase the source availability and reliability, in order to meet the requirement of a driver for an ADS system. The final design of TRIPS is shown in 2 The gaps, the voltage and the extraction holes have been designed in order to reduce the length of the extraction zone (where the beam is uncompensated) and to reduce the aperture-lens effect. Rms normalized emittance below 0.2π mm mrad (including the beam halo) have been calculated EXPERIMENTAL RESULTS CONCLUSION AND FUTURE DEVELOPMENTS In table 1 the status of the source is compared with the requirements of the TRASCO project. The requested reliability at 80 kV is not yet achieved, but the source performance are already good in terms of beam intensity, reproducibility and stability. The innovative solutions presented above have confirmed their validity. We are confident that in a few months a more significant reliability test at 80 3 kV (over two weeks) can be done. As this goal will be accomplished, the emittance measurements can be done with a similar emittance measuring device as the one described in ACKNOWLEDGEMENT

Application of Ferroelectric Cathodes to Enhance the Ion Yield in the Caesar Source at LNS

With increasing RF power the electron concentration in the plasma of ECR ion sources is decreasing in comparison to the ion concentration, so that the plasma is charging up positively. Direct injection of electrons into the ECR plasma can increase the electron charge density and the ion current yield. We have used ferroelectric cathodes to inject electrons into the Argon plasma of the CAESAR ion source at INFN-LNS (Catania, Italy). The cathode was placed at about 10 cm from the hot plasma and a bipolar high voltage pulse of 1.6 kV was used to trigger the electron emission. No additional acceleration has been provided. The use of the ferroelectric cathode leads to an increase of about 30% of the Ar8+ intensity, which has been monitored during the test. In addition, magneto-hydrodynamic instabilities in the ECR source were damped during and after electron injection

Multicharged Carbon Ion Generation from Laser Plasma

Carbon ions generated by ablation of a carbon target using an Nd:YAG laser pulse (wavelength λ = 1064 nm, pulse width τ = 7 ns, and laser fluence of 10-110 J cm-2) are characterized. Time-of-flight analyzer, a three-mesh retarding field analyzer, and an electrostatic ion energy analyzer are used to study the charge and energy of carbon ions generated by laser ablation. The dependencies of the ion signal on the laser fluence, laser focal point position relative to target surface, and the acceleration voltage are described. Up to C4+ ions are observed. When no acceleration voltage is applied between the carbon target and a grounded mesh in front of the target, ion energies up to ∼400 eV/charge are observed. The time-of-flight signal is analyzed for different retarding field voltages in order to obtain the ion kinetic energy distribution. The ablation and Coulomb energies developed in the laser plasma are obtained from deconvolution of the ion time-of-flight signal. Deconvolution of the time-of-flight ion signal to resolve the contribution of each ion charge is accomplished using data from a retarding field analysis combined with the time-of-flight signal. The ion energy and charge state increase with the laser fluence. The position of the laser focal spot affects the ion generation, with focusing ∼1.9 mm in front of the target surface yielding maximum ions. When an external electric field is applied in an ion drift region between the target and a grounded mesh parallel to the target, fast ions are extracted and separated, in time, due to increased acceleration with charge state. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4966987

Production of intense highly charged ion beams with SERSE

The source SERSE is operational at LNS since June 1998 and many improvements have been carried out in this period. The frequency has been increased from 14.5 GHz to 18 GHz and the use of two frequency heating has given positive results. Metallic ion production has been tested by means of a high temperature oven and the preliminary results are described. Tests of magnetic field scaling and frequency scaling have confirmed the results of previous tests with SC-ECRIS at lower frequency and seems to suggest that the upgrading of the source to higher frequency may be considered