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International audience; Theoretical predictions as well as experiments performed at storage rings have shown that the lifetimes of β-radionuclides can change significantly as a function of the ionization state. In this paper we describe an innovative approach, based on the use of a compact plasma trap to emulate selected stellar-like conditions. It has been proposed within the PANDORA project (Plasmas for Astrophysics, Nuclear Decay Observation and Radiation for Archaeometry) with the aim to measure, for the first time in plasma, nuclear β-decay rates of radionuclides involved in nuclear-astrophysics processes. To achieve this task, a compact magnetic plasma trap has been designed to reach the needed plasma densities, temperatures, and charge-states distributions. A multi-diagnostic setup will monitor, on-line, the plasma parameters, which will be correlated with the decay rate of the radionuclides. The latter will be measured through the detection of the γ-rays emitted by the excited daughter nuclei following the β-decay. An array of 14 HPGe detectors placed around the trap will be used to detect the emitted γ-rays. For the first experimental campaign three isotopes, 176Lu, 134Cs, and 94Nb, were selected as possible physics cases. The newly designed plasma trap will also represent a tool of choice to measure the plasma opacities in a broad spectrum of plasma conditions, experimentally poorly known but that have a great impact on the energy transport and spectroscopic observations of many astrophysical objects. Status and perspectives of the project will be highlighted in the paper.

International audience; Cumulative ion confinement times are probed by measuring decaying ion current transients in pulsed material injection mode. The method is applied in a charge breeder and conventional ECRIS yielding mutually corroborative results. The cumulative confinement time estimates vary from approximately 2 ms–60 ms with a clear dependence on the ion charge-to-mass ratio—higher charges having longer residence times. The long cumulative confinement times are proposed as a partial explanation to recently observed unexpectedly high ion temperatures. The results are relevant for rare ion beam (RIB) production as the confinement time and the lifetime of stable isotopes can be used for estimating the extracted RIB production efficiency.

This paper reports the effects of sinusoidal microwave power Amplitude Modulation (AM) on the performance of Electron Cyclotron Resonance (ECR) ion sources. The study was conducted on the 14 GHz ECR ion source ECR2 at the University of Jyväskylä. The klystron output was intentionally altered by a variable frequency sinusoidal amplitude modulation. The average microwave power 350 W was modulated between 530 W and 180 W from 0.011-25 kHz. The integrated x-ray energy, the mass analyzed beam current and the forward and reflected microwave power were measured. The energy integrated x-ray signal responded strongly with low frequency modulation and was no longer observable at approximately 2.2 kHz where the signal strength became solely dependent on the time averaged power. The beam current responded in a similar way but exhibited a strong dependence with magnetic field. Qualitatively, we found source tuning parameters where AM effects were reduced also produced the highest currents of Ne8+ in Continuous Wave (CW) mode. Furthermore, these parameters are typically used for optimized beam injection into the K130 cyclotron. The dependence of beam current and the x-ray signal modulation on AM frequency for different magnetic fields are reported. A qualitative interpretation of the results will be given. peerReviewed

International audience; PSC has developed the PHOENIX electron cyclotron resonance Charge Breeder since 2000. The performances have been improved over time acting on the 1+ and N+ beam optics, the base vacuum and the 1+ beam injection. A new objective is to update the booster design to enhance high charge state production and 1+ N+ efficiencies, reduce the co-extracted background beam and improve the ion source tunability. The first step, consisting in increasing the peak magnetic field at injection from 1.2 T to 1.6 T was implemented and significant improvement in 1+N+ efficiencies are reported: 12.9% of 23Na8+, 24.2% of 40Ar8+, 13.3% of 132Xe26+ and 13% of 133Cs26+. The next steps of the upgrade are presented: modification of the axial magnetic structure, significant increase of the plasma chamber radius (72 to 90 mm), plasma heating at 18 GHz (instead of 14 GHz), reduction of chemical elements composing the plasma chamber wall and the surrounding beam line.

The production of Ar9+ and Ar13+ ions in an ECRIS plasma and the efficiency of the ion beam extraction and transport of the resulting Ar9+ and Ar13+ ion beams have been studied with the JYFL 14 GHz ECRIS by using optical emission spectroscopy and measurement of the m/q analyzed beam currents. The relative changes in both the optical emission and the ion beam current in CW mode as function of microwave power and in amplitude modulation (AM) operation mode are reported. The results indicate a discrepancy between the parametric dependence of high charge state ion densities in the core plasma and their extracted beam currents. The observation implies that in CW mode the ion currents could be limited by diffusion transport and electrostatic confinement of the ions rather than beam formation in the extraction region and subsequent transport. peerReviewed

Experimental results of low temperature hydrogen plasma induced photoelectron emission measurements comparing two different plasma heating methods are summarized. By exposing the samples to the vacuum ultraviolet radiation of a filament-driven multi-cusp arc discharge ion source and a 2.45 GHz microwave-driven ion source, it has been measured that the total photoelectron emission from various metal surfaces is on the order of 1 A per kW of plasma heating power, which can be increased by a factor of 2–3.5 with a thin layer of alkali metal. The possible effects of the photoelectrons on the plasma sheath structure are studied with a 1D collisionless model extended to include the contribution of photoelectron emission from the surface.Experimental results of low temperature hydrogen plasma induced photoelectron emission measurements comparing two different plasma heating methods are summarized. By exposing the samples to the vacuum ultraviolet radiation of a filament-driven multi-cusp arc discharge ion source and a 2.45 GHz microwave-driven ion source, it has been measured that the total photoelectron emission from various metal surfaces is on the order of 1 A per kW of plasma heating power, which can be increased by a factor of 2–3.5 with a thin layer of alkali metal. The possible effects of the photoelectrons on the plasma sheath structure are studied with a 1D collisionless model extended to include the contribution of photoelectron emission from the surface.

The experimental and theoretical research carried out in the past at the Institute of Applied Physics (IAP RAS) resulted in development of a new type of electron cyclotron resonance ion source (ECRIS) – the gasdynamic ECRIS. The gasdynamic ECRIS features a confinement mechanism in a magnetic trap that is different from Geller’s classical ECRIS confinement i.e. the quasi-gasdynamic one similar to that in fusion mirror traps . Such ion source type has demonstrated good performance producing high current (100-300 mA) multi-charged ion beams with moderate average charge (Z=4-5 for argon) and especially high efficiency for low emittance hydrogen and deuterium beam formation (500 emA current, current density up to 700 emA/cm2 and RMS emittance below 0.07 π·mm·mrad). Experimental studies of gasdynamic ECRIS in a pulsed mode were performed at SMIS 37 facility.The obtained high-level results have stimulated a wide spectrum of research activities devoted to further extension of the gasdynamic ECR source principles to related fields of research and applications. The present report overviews recent investigations at the Ion Sources Laboratory connected with ECR plasma heating by powerful millimeter wave gyrotron radiation. Novel ideas such as using a magnetic field generated by a single coil for plasma quasigasdynamic confinement for proton beams production, applications of a dense ECR plasma for H- generation, development of a new CW gasdynamic ECR source with 28 GHz gyrotron heating among others are discussed. peerReviewed

Acetylene and carbon dioxide gases are used in a filament-powered volume-cusp ion source to produce negative carbon ions for the purpose of carbon implantation for gettering applications. The beam was extracted to an energy of 25 keV and the composition was analyzed with a spectrometer system consisting of a 90° dipole magnet and a pair of slits. It is found that acetylene produces mostly C−2 ions (up to 92 µA), while carbon dioxide produces mostly O− with only trace amounts of C−. Maximum C−2 current was achieved with 400 W of arc power and, the beam current and composition were found to be highly dependent on the pressure in the source. The beam properties as a function of source settings are analyzed, and plasma properties are measured with a Langmuir probe. Finally, we describe testing of a new RF H− ion source, found to produce more than 6 mA of CW H− beam. peerReviewed

Photoelectron emission measurements have been performed using a 2.45 GHz ECR-driven multi-dipolar plasma source in a low pressure hydrogen discharge. Photoelectron currents induced by light emitted from ECR zone and H− production region are measured from Al, Cu, Mo, Ta, and stainless steel (SAE 304) surfaces as a function of microwave power and neutral hydrogen pressure. The total photoelectron current from the plasma chamber wall is estimated to reach values up to 1 A for 900 W of injected microwave power. It is concluded that the volumetric photon emission rate in wavelength range relevant for photoelectron emission is a few times higher in arc discharge. peerReviewed

Atomic layer deposition (ALD) is a method for thin film fabrication with atomic level precision. This thesis focuses on low-temperature thermal and plasma- enhanced ALD and presents results on thin film growth by these techniques with examples of common ALD materials: Al2O3, ZnO and TiO2. As an example of limitations of the thermal ALD the nucleation and growth of Al2O3 and ZnO films on different grades of poly(methyl methacrylate) (PMMA) are presented, showing that the initiation of the growth is strongly dependent on both the deposited material and the substrate. A potential application of the ALD ZnO films in polymer surface functionalization is demonstrated by changing in the surface wettability by means of UV-illumination. To overcome the nucleation delay in thermal ALD, room-temperature PEALD of ZnO films was demonstrated. It is shown that the growth and properties of the films depend on the PEALD reactor configuration and the plasma conditions therein. The plasma species interactions shown to be beneficial to the film growth were observed to damage the polymer substrates, the severeness depending on the polymer material. The last part of this thesis describes plasma mode transitions in capacitively- and inductively-coupled plasmas, that are typically used in PEALD processing. In addition to the mode transition induced changes in the plasma parameters, the contribution of the different plasma species to the growth and properties of ZnO and TiO2 films are demonstrated and discussed.

“Prometheus I” is a volume H− negative ion source, driven by a network of dipolar electron cyclotron resonance (ECR; 2.45 GHz) modules. The vacuum-ultraviolet (VUV) emission spectrum of low-temperature hydrogen plasmas may be related to molecular and atomic processes involved directly or indirectly in the production of negative ions. In this work, VUV spectroscopy has been performed in the above source, Prometheus I, both in the ECR zones and the bulk (far from ECR zones and surfaces) plasma. The acquired VUV spectra are correlated with the negative ion densities, as measured by means of laser photodetachment, and the possible mechanisms of negative ion production are considered. The well-established H− formation process of dissociative attachment to vibrationally excited molecules is evaluated, while an additional production path (i.e. neutral resonant ionization) is tested due to the recently attracted interest. The obtained results indicate that for the source Prometheus I, the dominant formation process is dissociative attachment. peerReviewed