T. Thuillier

Status of charge breeding with electron cyclotron resonance ion sources (invited)

Due to the production methods of exotic nuclei, an efficient acceleration of radioactive ion beams needs charge breeding of weakly charged ions. The upgrade of existing isotope separator on-line facilities (TRIUMF-isotope separation and acceleration, CERN-isotope separation on-line detector, etc.) or the development of projects for the acceleration of radioactive ion beams (GANIL-SPIRAL2, MAFF, EURISOL, etc.) requires charge breeders with high efficiency, fast charge breeding time, low background levels, and high intensity acceptance either in continuous or in pulsed mode. The optimization of these parameters is a challenge for the electron cyclotron resonance (ECR) community and is useful to get a better understanding of plasma physics in ECR ion sources (ECRISs). The ECR charge breeding technique has been developed for more than ten years at LPSC (former ISN) Grenoble, typical 1+→n+ efficiencies are in the 3%–10% range depending on the nature of the incoming beam (metallic, alkaline, and gaseous) and re...

Experimental and Theoretical Investigation of the Preglow in ECRIS

The experimental study of the pulsed-mode operation of the PHOENIX-V2 electron cyclotron resonance ion source at 28 GHz has clearly demonstrated, when increasing the repetition rate of the high-frequency power injection at frequencies higher than 1 Hz, the reality of a transient current peak occurring at the very beginning of the plasma discharge. This regime was named Preglow as an explicit reference to the classical Afterglow occurring at the microwave pulse end. After the transient Preglow peak, the plasma regime relaxes to the classical steady-state one. Experimental argon pulses for charge states from 2+ to 8+ are presented. The current observed during the Preglow peak can reach intensities on the order of 1 mA for low charge states (Ar4+). A zero-dimension theoretical model of electron cyclotron resonance (ECR) gas breakdown in a magnetic trap is presented in detail. Results of the simulation are compared with the experimental Preglow peaks and discussed.

Charge state breeding applications with the ECR PHOENIX source: From low to high current production

The electron cyclotron resonance (ECR) charge state breeding method based on the PHOENIX source is first dedicated to the continuous high charge state radioactive ion production for cyclotrons, due to their q/m requirements, and to the high charge state production efficiency. It can be used as an injector for RFQ, linacs, and synchrotrons either in cw or pulsed operation. The efficiency of the 1+ to the n+ ion production and the charge breeding time are the fundamental parameters of the method, their dependence with regard to the 1+ ion beam emittance injected has been measured and will be discussed with regard to the radioactive ion beam acceleration. The efficiency of the process slightly decreases when injecting ion beam emittances higher than 30 π mm mrad, and remains constant in the 1+ radioactive intensity range available today and in the future. The ECR ion trap tuning associated with the afterglow mode permits the ionization, the accumulation, and the extraction of the injected primary beam keepin...

ECRIS development for stable and radioactive pulsed beams

The latest 28 and 37.5 GHz developments show that very intense pulsed beams of medium charge states can be produced with an ECRIS. We will present latest results obtained with PHOENIX 28 GHz in afterglow mode operation and specially the capacity of the source to produce high current of medium charge states despite a relatively low radial magnetic confinement system. Initially, these developments have been made for Pbn+ ion production for the LHC. A program is now underway by using a very strong ionic pumping effect in order to produce highly bunched beams of radioactive ions suitable for synchrotron acceleration for the CERN Beta-beam project. The purpose of this program consists of producing about 1012 of 6He or 18Ne ions/bunch within 100 μs pulse durations and with a 10 Hz repetition rate. This development must use two ECRIS advantages: the gas efficiency and the bunching capability. We will present a concept showing how we can bunch and ionize the radioactive gas injected in a cw operation source. Expe...

High current density production of multicharged ions with ECR plasma heated by gyrotron transmitter

In order to study the possibilities to produce high currents of pulsed heavy ion beams dedicated to synchrotron injection, two new approaches of ECR devices are now underway. The basic principle consists in maintaining a functioning point of the source with the highest density as possible and a minimum confinement time for the production of a given charge state. It means that for a constant neτi product we try to maximize ne and minimize τi. For this purpose two experiments are in progress at ISN/Grenoblea and IAP/Nizhny Novgorod.b The first one consists of using a minimum |B| magnetic structure with a 1.8 mirror ratio characteristic value with a 28 GHz frequency injection. In this case we explore different functioning points up to 10 kW of UHF power. The second one consists of a simple mirror magnetic system (simple mirror ion source, SMIS) working at 37.5 GHz with a mirror ratio up to 3 (2.5 T) where we study discharges with a peak power up to 100 kW. We will show that, in spite of a very short rising t...

Ultracompact/ultralow power electron cyclotron resonance ion source for multipurpose applications

In order to drastically reduce the power consumption of a microwave ion source, we have studied some specific discharge cavity geometries in order to reduce the operating point below 1 W of microwave power (at 2.45 GHz). We show that it is possible to drive an electron cyclotron resonance ion source with a transmitter technology similar to those used for cellular phones. By the reduction in the size and of the required microwave power, we have developed a new type of ultralow cost ion sources. This microwave discharge system (called COMIC, for COmpact MIcrowave and Coaxial) can be used as a source of light, plasma or ions. We will show geometries of conductive cavities where it is possible, in a 20 mm diameter chamber, to reduce the ignition of the plasma below 100 mW and define typical operating points around 5 W. Inside a simple vacuum chamber it is easy to place the source and its extraction system anywhere and fully under vacuum. In that case, current densities from 0.1 to 10 mA/cm(2) (Ar, extraction 4 mm, 1 mAe, 20 kV) have been observed. Preliminary measurements and calculations show the possibility, with a two electrodes system, to extract beams within a low emittance. The first application for these ion sources is the ion injection for charge breeding, surface analyzing system and surface treatment. For this purpose, a very small extraction hole is used (typically 3/10 mm for a 3 microA extracted current with 2 W of HF power). Mass spectrum and emittance measurements will be presented. In these conditions, values down to 1 pi mm mrad at 15 kV (1sigma) are observed, thus very close to the ones currently observed for a surface ionization source. A major interest of this approach is the possibility to connect together several COMIC devices. We will introduce some new on-going developments such as sources for high voltage implantation platforms, fully quartz radioactive ion source at ISOLDE or large plasma generators for plasma immersion, broad or ribbon beams generation.

Gas breakdown in electron cyclotron resonance ion sources

The realization of the beta-beam project (http://beta-beam.web.cern.ch/beta-beam/) assumes the formation of a pulsed ion beam of helium and neon radioactive isotopes. A pulsed electron cyclotron resonance (ECR) source of multicharged ions has been proposed to produce such a beam [P. Sortais et al., Rev. Sci. Instrum. 75, 1610 (2004)]. The rising of plasma density up to a stationary level must be fast enough to actualize this approach. This condition is mandatory to avoid particle losses in the transmission line. In the presented work, the rising time of the plasma density in an ECR ion source from a background level up to 98% of a stationary level is calculated. A zero-dimensional model of plasma formation in a mirror trap [V. Semenov et al., Rev. Sci. Instrum. 73, 635 (2002)] is used, able to make calculation for a wide range of microwave frequencies. Plasma confinement regime can either be classic (Pastoukhov [Rev. Plasma Phys. 13, 203 (1987)]) or gas dynamic, depending on the plasma parameters. The cal...

Ion beam formation in a gas-dynamic electron cyclotron resonance ion source

Generation of quasistationary flows of multicharged ions with a current density of up to 1A∕cm2 from a dense electron cyclotron resonance plasma confined in a magnetic trap under the quasi-gas-dynamic regime has been achieved [Golubev et al., Trans. Fusion Sci. Technol. 47, 345 (2005)]. This technique provides opportunities for extracting high current multicharged ion beams. The present research is concerned with experimental and theoretical investigations of two ion extraction systems for the gas-dynamic ion sources. (1) Single-aperture system. In this case, there is a principal possibility to obtain ion beams with low emittance by using a small-diameter aperture for extraction. Here we describe investigations aimed at creating nitrogen ion beams (the main ion in the spectrum is N2+) with currents of up to 6.5mA through a 1.5mm aperture in the plasma electrode. (2) Multiaperture system. Such systems provide significantly higher beam currents. First results of testing an extractor with five apertures are ...

Beam injection improvement for electron cyclotron resonance charge breeders.

The injection of a 1+ beam into an electron cyclotron resonance (ECR) charge breeder is classically performed through a grounded tube placed on its axis at the injection side. This tube presents various disadvantages for the operation of an ECR charge breeder. First experiments without a grounded tube show a better use of the microwave power and a better charge breeding efficiency. The optical acceptance of the charge breeder without decelerating tube allows the injection of high intensity 1+ ion beams at high energy, allowing metals sputtering inside the ion source. The use of this method for refractory metallic ion beams production is evaluated.

A-PHOENIX, an electron cyclotron resonance ion source for the Spiral 2 facility

Spiral 2, the radioactive ion-beam facility of GANIL, will start its commissioning in 2009. After a brief recall of Spiral 2 beam requirements, emittance measurements of preliminary 1mA O6+ test beams, done with the PHOENIX source for Spiral 2, are shown and discussed. The 28GHz A-PHOENIX source, designed to better meet the Spiral 2 requirements, is presented and a progress report of its construction is proposed.