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ABSTRACT: The high intensity ion source (SILHI), in operation at CEA-Saclay, has been used to produce a 90 mA pulsed proton beam with pulse length and repetition rates suitable for the European Spallation Source (ESS) linac. Typical r-r(') rms normalized emittance values smaller than 0.2π mm mrad have been measured for operation in pulsed mode (0.01 < duty cycle < 0.15 and 1 ms < pulse duration < 10 ms) that are relevant for the design update of the Linac to be used at the ESS in Lund.
The Review of scientific instruments 05/2012; 83(5):056109. · 1.52 Impact Factor
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ABSTRACT: The versatile ion source (VIS) is an off-resonance microwave discharge ion source which generates a slightly overdense plasma (n(e) ≈ 10(17) cm(-3)) operating at 2.45 GHz and producing more than 50 mA of proton beams. A detailed characterization of the source, by operating between 60 and 75 kV, in terms of emittance, current extracted and proton fraction is reported below. Moreover, passive techniques (alumina coating of the plasma chamber walls, BN disks at the injection and extraction endplates) have been used to improve the performance of the source, increasing the electron density for a more efficient ionization. The know-how achieved with the VIS source may be useful for the different project, particularly for the European spallation source.
The Review of scientific instruments 02/2012; 83(2):02A305. · 1.52 Impact Factor
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ABSTRACT: The diffusion mechanism in magnetized plasmas is a largely debated issue. A short circuit model was proposed by Simon, assuming fluxes of lost particles along the axial (electrons) and radial (ions) directions which can be compensated, to preserve the quasi-neutrality, by currents flowing throughout the conducting plasma chamber walls. We hereby propose a new method to modify Simon's currents via electrons injected by a carbon nanotubes-based electron gun. We found this improves the source performances, increasing the output current for several charge states. The method is especially sensitive to the pumping frequency. Output currents for given charge states, at different auxiliary electron currents, will be reported in the paper and the influence of the frequency tuning on the compensation mechanism will be discussed.
The Review of scientific instruments 02/2012; 83(2):02A343. · 1.52 Impact Factor
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G Castro,
D Mascali,
F P Romano,
L Celona,
S Gammino,
D Lanaia,
R Di Giugno, R Miracoli,
T Serafino,
F Di Bartolo,
N Gambino,
G Ciavola
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ABSTRACT: A microwave discharge ion source (MDIS) operating at the Laboratori Nazionali del Sud of INFN, Catania has been used to compare the traditional electron cyclotron resonance (ECR) heating with an innovative mechanisms of plasma ignition based on the electrostatic Bernstein waves (EBW). EBW are obtained via the inner plasma electromagnetic-to-electrostatic wave conversion and they are absorbed by the plasma at cyclotron resonance harmonics. The heating of plasma by means of EBW at particular frequencies enabled us to reach densities much larger than the cutoff ones. Evidences of EBW generation and absorption together with X-ray emissions due to high energy electrons will be shown. A characterization of the discharge heating process in MDISs as a generalization of the ECR heating mechanism by means of ray tracing will be shown in order to highlight the fundamental physical differences between ECR and EBW heating.
The Review of scientific instruments 02/2012; 83(2):02B501. · 1.52 Impact Factor
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ABSTRACT: The time and space resolved characterization of laser-generated pulsed plasmas is useful not only for the comprehension of basic phenomena involved in the plasma generation and following supersonic expansion, but it also permits to control the nonequilibrium process that is useful for many applications (e.g., ion implantation). The “on-line” characterization can be performed by means of Langmuir probes, ion collectors, and ion energy analyzers, in order to measure the plasma temperatures and densities of atoms, ions, and electrons. The investigated plasmas were generated by means of laser pulses with intensity of the order of 10<sup>9</sup> W / cm <sup>2</sup> . The contemporary characterization of the electron (through the Langmuir probe) and ion energy distribution functions, EEDF and IEDF, respectively, permits to correlate the ion properties, like charge states and temperatures, with the electron properties, like the shape of the EEDF at different times and distances from the ablated target surface.
Journal of Applied Physics 07/2010; · 2.17 Impact Factor
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ABSTRACT: The modeling of laser-generated plasmas can be carried out by means of different theoretical approaches. Hydrodynamic simulations have the advantage of treating the plasma as a continuous fluid that expands in vacuum with a high Mach number. We used the analytical Anisimov model for the numerical simulations of a plasma expanding at supersonic velocities. The model describes the plume by means of a special solution of the gas dynamical equations on the hypothesis that the flow expands adiabatically. Here, we carry out a comparative analysis between experimental and numerical results: the model fits the experimental data for monoatomic plumes quite well. More specifically, the numerical data have been tested by comparing the time-of-flight signals obtained at the INFN-LNS in Catania from a pure metallic target. A Coulomb drift velocity was added to the expansion velocity, and only in this way was it possible to explain the experimental results, thus confirming the presence of self-generated electrostatic fields inside the expanding plasma plume.
Radiation Effects & Defects in Solids: Incorporating Plasma Science & Plasma Technology. 06/2010; 165(6-10):543-550.
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ABSTRACT: Laser-generated plasmas, formed when a high power pulsed laser is focused onto a solid target, have been used since the 1960s. At higher power densities (>109–1010 W/cm2), such non-equilibrium plasmas expand in vacuum with supersonic velocities. Hydrodynamic simulations and experimental data show that at the beginning of the expansion the plasma temperature may reach several hundreds of eV, while the density is in the order of 1016 cm−3 or higher. Colliding laser-produced plasmas have constituted a largely unexplored and unexploited research domain until quite recent times, either for applications in materials or energy science. In this article, we propose the use of colliding laser-produced plasmas as an unique opportunity for nuclear astrophysics studies. We present a series of calculations about fusion reaction rates in laser-produced plasmas where the electron screening puzzle is taken into account. The numerical simulations have been carried out using the hydro code ZEUSMP2, while Monte Carlo codes have been used to simulate the fusion reaction rates according to the plume density and temperature evolution predicted by the simulations. We think that this type of investigation can be important in understanding the efficiency of nuclear reaction rates during the red giant phase of stellar evolution, as a significant part of the produced energy is dissipated in the low-density radiative envelope by shock waves.
Radiation Effects & Defects in Solids: Incorporating Plasma Science & Plasma Technology. 06/2010; 165(6-10):730-736.
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ABSTRACT: The most effective devices able to feed modern accelerators with heavy ions (either in terms of reliability or performance) are electron cyclotron resonance ion sources (ECRIS), which are able to generate intense currents of multiply charged ions. One of the disadvantages of the ECRIS consists of the limitation in the production of metallic ions (usually obtained by means of ovens and sputtering techniques), especially in the case of refractory elements. Laser ablation is an effective method for such elements. The coupling between a laser ion source (LIS) and an ECRIS has been studied at some facilities (INFN-LNS, RIKEN, University of Frankfurt, ANL): the experiments were successful but an adequate modeling and additional experimental activities are mandatory. Preliminary calculations have shown that the ion energy from the LIS should be lower than a few hundreds of eV in order to permit an effective coupling of LIS ions with the ECRIS plasma. A detailed investigation of the ion capture by the ECRIS plasma has now been carried out by means of numerical simulations based on the Monte Carlo method. The energy distribution function of the LIS plasma has been taken into account, as well as the density and temperature distribution of the ECRIS plasmas and the pattern of the magnetic field in the resonance region. The captured fraction of LIS ions strongly depends on the temperature (the lower energy component of the ion energy distribution function is easily absorbed by the ECRIS plasma). The effect of negatively biased targets has been also investigated: simulations demonstrate that for negative potentials of the order of 0.4 kV the captured fraction abruptly increases, and in some particular cases it exceeds 50% of the total ion current.
Radiation Effects & Defects in Solids: Incorporating Plasma Science & Plasma Technology. 06/2010; 165(6-10):472-480.
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ABSTRACT: A pulsed neodymium-doped yttrium aluminum garnet laser ion source has been used as proton beams generator. The laser wavelength is 1064 nm, the pulse duration is 9 ns and the intensity reaches 10(10) W/cm(2). Laser irradiates hydrogenated polymers targets located in a chamber at 10(-7) mbar. The ions are post-accelerated in a suitable chamber by 30 kV of voltage between the target, positively biased, and the following ground electrode. The extracted beams is characterized through a time-of-flight technique. Possible applications to the field of nuclear physics, such as nuclear excitation and de-excitations, nuclear reactions and nuclear fusion, will be presented and discussed.
The Review of scientific instruments 02/2010; 81(2):02A508. · 1.52 Impact Factor
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ABSTRACT: In electron cyclotron resonance ion sources it has been demonstrated that plasma heating may be improved by means of different microwave to plasma coupling mechanisms, including the "frequency tuning" and the "two frequency heating." These techniques affect evidently the electron dynamics, but the relationship with the ion dynamics has not been investigated in details up to now. Here we will try to outline these relations: through the study of ion dynamics we may try to understand how to optimize the electron cyclotron resonance ion sources brightness. A simple model of the ion confinement and beam formation will be presented, based on particle-in-cell and single particle simulations.
The Review of scientific instruments 02/2010; 81(2):02A334. · 1.52 Impact Factor
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http://dx.doi.org/10.1140/epjd/e2010-00244-y.
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ABSTRACT: A set of measurements has been carried out at INFN-LNS on a plasma reactor used for environmental applications with the aim to characterize it in terms of possible excited resonant modes inside the cavity with and without plasma. The results have put in evidence that resonant modes are excited inside the cavity and standing waves are formed even in presence of a dense plasma. The measurement of the eigen-frequency shift, which occurs after the plasma ignition, has been carried out, for several values of pressure and power. The changes in plasma shape, density and electron temperature have been also monitored for different operating conditions by means of a Langmuir Probe. Such measurements are also relevant for the ECR Ion Sources, as they confirm that the variation of their performances with the frequency can be explained by considering that resonant modes are excited inside the plasma chamber even in presence of a dense plasma.
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ABSTRACT: The sources adapted to beam production for high power proton accelerators must obey to the request of high brightness, stability and reliability. The Versatile Ion Source (VIS) is based on permanent magnets to produce an off-resonance microwave discharge (the maximum field value on the chamber axis is around 0.1 T). It operates up to 75 kV without a bulky high voltage platform, producing several tens of mA of proton beams and monocharged ions. The microwave injection system and the extraction electrodes geometry have been designed in order to optimize the beam brightness. Moreover, the VIS source ensures long time operations without maintenance and high reliability. A description of the main components and of the source performances is given in the following. A brief summary of the possible next developments is also presented, particularly for pulsed mode operations, that are relevant for some future projects (e.g. the European Spallation Source of Lund).
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ABSTRACT: A plasma reactor operates at the Laboratori Nazionali del Sud of INFN, Catania, and it has been used as a test-bench for the investigation of innovative mechanisms of plasma ignition based on electrostatic waves (ES-W), obtained via the inner plasma EM-to-ES wave conversion. Evidences of Bernstein wave (BW) generation will be shown. The Langmuir probe measurements have revealed a strong increase of the ion saturation current, where the BW are generated or absorbed, this being a signature of possible high energy ion flows. The results are interpreted through the Bernstein wave heating theory, which predicts the formation of high speed rotating layers of the plasma (a dense plasma ring is in fact observed). High intensity inner plasma self-generated electric fields (on the order of several tens of kV/cm) come out by our calculations.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 653(1):11-16. · 1.21 Impact Factor
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F Odorici,
M Cuffiani,
L Malferrari,
R Rizzoli,
G P Veronese,
L Celona,
S Gammino,
D Mascali, R Miracoli,
F P Romano,
N Gambino,
G Castro,
G Ciavola
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ABSTRACT: The CANTES experiment at INFN-LNS tested the use of carbon nanotubes (CNTs) to emit electrons by field emission effect, in order to provide additional electrons to the plasma core of an ECR ion source. This technique was used with the Caesar source, demonstrating that the total extracted ion current is increased and that a relevant reduction of the number of "high energy" electrons (above 100 keV) may be observed. The injection of additional electrons inside the plasma increases the amount of cold and warm electrons, and then the number of ionizing collisions. Details of the construction of CNTs based electron gun and of the improvement of performances of the Caesar ECR ion source will be presented.
