MeV Heavy Ion Research Articles

Ion Tracks in Metals and Intermetallic Compounds

When an energetic ion penetrates a target, it loses its energy via two nearly independent processes: (1) elastic collisions with the nuclei (nuclear-energy loss (dE/dx)n), which dominate the ion slowing down in the low energy range (i.e., in the stopping region); (2) electronic excitation and ionization (electronic-energy loss (dE/dx)e), which strongly overwhelm (dE/dx)n in the high energy range (typically above 1 MeV/nucleon). Until the 1980s, researchers considered that electronic-energy deposition could participate in damaging creation in many insulators, but the effects observed in bulk metals were solely ascribed to elastic nuclear collisions. This widely held opinion was due to the fact that in metallic systems the numerous very mobile conduction electrons allow a fast spreading of the deposited energy and an efficient screening of the space charge created in the projectile wake so that it seemed unreasonable to hope for damage creation or track formation in metallic targets following high levels of electronic-energy deposition.A particular case is the observation more than 30 years ago of damage in thin or discontinuous. metallic films after fission fragment irradiation or MeV heavy ion bombardment. The spreading of the deposited energy is then strongly limited by the close vicinity of surfaces and interfaces.

Characterization of the electric field and gain of the 2 MeV energy analyzer (abstract)

Accurate determination of plasma potentials in the TEXT-upgrade tokamak using the 2 MeV heavy ion beam probe requires a good understanding of detector characteristics. The detector utilized is a parallel plate electrostatic energy analyzer. A figure of merit for this analyzer is the gain, GA, which is defined as the ratio of the potential of the incident ions to the potential applied to the analyzer anode. Tests are in progress on the vertical test stand at Rensselaera) to characterize the dependence of gain on radial entrance angle, toroidal entrance angle, and toroidal position of the ion beam. Results will be used to assist with in situ calibration on the TEXT-upgrade facility.

Design of improved electric potential fluctuation detector for 2 MeV heavy ion beam probe on TEXT (abstract)

The present detector system used for the TEXT heavy ion beam probe (HIBP) is not sensitive to potential fluctuations of magnitude below 10−5×Vacc where Vacc is the accelerator voltage. With the upgrade of the TEXT HIBP to 2 MeV, the minimum detectable fluctuation is on the order of 10 V under optimum conditions. A new detector system has been proposed, and a proof-of-concept experiment has indicated that it should be sensitive to fluctuations on the order of 1 V. The new system separates the ion beam entering the energy analyzer into ten smaller beams. The fluctuations in each smaller beam are measured individually, effectively increasing the signal by a factor of 10 without increasing detector noise. A version of the new detector system is presented that is designed specifically for the high-energy analyzer of the 2 MeV TEXT HIBP. In addition to the improved detector set, this design includes a standard detector set for side-by-side comparison, as well as for measuring other plasma parameters.

Plasma potential measurements on text-upgrade with a 2 MeV heavy ion beam probe (abstract)a)

The plasma potential is measured in TEXT-upgrade tokamak by injection and detection of high energy heavy ions (thallium and cesium with a single charge) using a 2 MeV accelerator and a parallel plate energy analyzer. The change in beam energy, as it crosses the plasma, gives the local plasma potential at the measurement volume. Recent results of high energy beam operations are presented.

Densification, anisotropic deformation, and plastic flow of SiO2 during MeV heavy ion irradiation

The response of SiO2 thin films and implantation masks to 4.0 MeV Xe irradiation is studied. Trenches in silica deform dramatically after irradiation with 3×1015 ions/cm2. In situ wafer curvature measurements show that thin planar silica films first densify by 3.6% during irradiation. The resulting stress then relaxes viscously by radiation-enhanced Newtonian flow. At a flux of 3×1010 Xe ions/cm2s the measured shear viscosity was 6×1013Pa s. We find evidence that an irradiation induced anisotropic deformation mechanism is present in the silica films. In equilibrium, this deformation leads to an average compressive saturation stress as large as 4.5×107 Pa.

ILSE Heavy Ion Accelerator

Lawrence Berkeley Laboratory (LBL) and Lawrence Livermore National Laboratory (LLNL) propose to build at LBL the Induction Linac Systems Experiments (ILSE), the next logical step towards the eventual goal of a heavy-ion induction accelerator powerful enough to implode or {open_quotes}drive{close_quotes} inertial-confinement fusion targets. ILSE is a 10 MeV heavy ion accelerator system that will establish the beam dynamics understanding required for a heavy ion IFE driver. Space charge dominated beams with driver scale dimensions will be employed. ILSE, although much smaller than a driver, will be the first experiment at full driver scale in several important parameters. Most notable among these are line charge density and beam cross section. Nearly all accelerator components and beam manipulations needed for an inertial fusion energy (IFE) driver will be tested. The ILSE accelerator and research program will permit experimental study of those beam manipulations required of an induction linac inertial fusion driver that have not been tested sufficiently in previous experiments. ILSE is also an important step in driver technology development for heavy ion drivers.

MeV heavy ion microprobe PIXE for the analysis of the materials surface

Micro PIXE analysis using MeV phosphorus microprobes was performed to a surface structure which consists of multilevel aluminum wirings in silicon nitride and these results were compared with those from a proton microprobe. In the case of a 2 MeV phosphorus microprobe, the X-ray production was enhanced near the surface due to the large energy deposition rate or the short projectile range. As a result, the increase in surface sensitivity was clearly shown in PIXE mapping images of aluminum, silicon, and phosphorus.

A 6 MeV heavy ion beam probe for the Large Helical Device

A 6 MeV heavy ion beam probe (HIBP) is being designed for potential measurements on the Large Helical Device (LHD). This article describes a method to control the 3-D probing beam trajectories in the helical magnetic field, an estimate of beam attenuation and energy reduction arising from the long paths in the plasma, and a cylindrical analyzer as a candidate for the energy analyzer.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Application of MeV heavy ion microprobes for PIXE measurements

MeV heavy ion microprobes, 3 MeV C 2+, Si 2+ and Ni 2+ were applied for micro-PIXE measurements for aluminium, silicon, copper, silver and gold substrates. To compare with the case of light ions, a 2 MeV H + microbeam was also employed. It was found that the X-ray yields vary drastically as a function of the combination of the atomic number of incident ions and target atoms. This indicates that there is an optimum combination for specific element analysis. The minimum detectable gold weights in silicon were also estimated for a practical case and it was found that a carbon beam was best for measuring gold atoms in silicon.

Microanalysis of materials by PIXE using focused MeV heavy ion beams

MeV heavy ion microprobes, 3 MeV C 2+, Si 2+ and Ni 2+ were applied for micro-PIXE measurements. It was found that the X-ray yields vary drastically as a function of the combination of the atomic number of incident ions and target atoms, which indicates that there is a best combination for specific element analysis. This was demonstrated by an investigation of human nail by a silicon microprobe which was compared with the case of proton. Furthermore, the minimum detectable gold weights in silicon were also estimated as a practical case and it was found that a carbon microprobe was best for measuring gold atoms in silicon.

Maskless fabrication of contact vias by focused MeV heavy ion beam

A focused MeV nickel ion beam was used for making contact vias in a multilayer structure through a passivation layer. The structures had two aluminum layers isolated by a Si 3N 4 insulating layer. The distribution of implanted nickel ions was controlled by changing the implantation energy. After the implantation, current-voltage characteristics between the two aluminum layers were measured by a two-point probe method. When the distribution of nickel was adjusted at the Si 3N 1 insulating layer, electrical conduction was observed at the nickel fluence of 1 × 10 17–2 × 10 18 ions/cm 2, and it was found that the conductivity was increased and the breakdown voltage was decreased as the fluence of nickel ions increased.

Microanalysis of masklessly MeV-ion-implanted area by MeV heavy-ion microprobe

Maskless MeV ion implantation into a silicon substrate and in-situ microanalysis before and after ion implantation by Rutherford backscattering spectrometry (RBS) or secondary electron (SE) detection using a heavy-ion microprobe were performed. The usefulness of the heavy-ion microprobe for microanalysis was shown.

Small-angle two-neutron and two-proton correlations in 30A MeV heavy-ion reactions.

Two-neutron correlations at small relative momentum in {sup 20}Ne+C and {sup 20}Ne+Co reactions at 30{ital A} MeV exhibit correlation functions dominated by the attractive final-state interaction. The results are consistent with two-proton data. The data suggest large apparent emission sources for both reactions with contributions from both pre-equilibrium emission and evaporation.

A focused MeV heavy ion beam line for materials modification and muanalysis

A beam line to focus a MeV heavy ion beam has been developed by combining a focusing system with a tandem-type accelerator. A beam spot size of 4 μm ×4 μm for carbon or gold ion beams is achieved with an energy range of 0.5–3 MeV. This enables us both maskless MeV ion implantation and in-situ muanalysis using heavy ions in a single system. Maskless MeV implantation of gold ions into a silicon substrate is demonstrated, and muanalysis of the implanted area is performed by secondary electron and RBS mapping images using 3 MeV C 2+ beams.

MeV ion-beam annealing of semiconductor structures

MeV heavy-ion beams have been used to induce epitaxial crystallization of amorphous Si, GaAs, InP, Ge-Si alloy and metal silicide layers. In all cases, the crystallization kinetics and the quality of the recrystallized layers have been compared with thermal-annealing behaviour. The most striking differences between the two annealing regimes (thermal and ion beam) have been observed for InP and high-dose In-implanted Si, where ion-beam annealing at low temperatures results in more extensive and higher-quality epitaxy than that achieved by thermal annealing.

HEAVY-ION BACKSCATTERING——A NEW METHOD FOR DETERMINATION OF TRACE HEAVY ELEMENTS ON THE SURFACE AND NEAR SURFACE

We describe a new technique for MeV heavy-ion backscattering analysis of trace heavy elements on the surface and near surface. Pulse pileup problems are eliminated by choice of incidence ion mass M1, which is the same as or larger then that of bulk atom M2. Using 3 MeV Si beam, we could measure quantities of arsenic implanted in silicon down to 2×1012 atoms/cm2. Experimental results also show that sensitivity for impurity element on silicon substrate is as high as 2.2 ×109 atoms/cm2 for Au.

Ion trajectory simulations for the TEXT upgrade 2 MeV heavy ion beam probe (abstract)

Ion trajectory calculations play a key role in the design of a heavy ion beam probe system and the interpretation of its measurements. In the case of the HIBP for TEXT Upgrade presently under construction, ion trajectory simulations showed that ions with energies up to 2 MeV have to be injected and detected at two different locations in order to make measurements over the whole plasma cross section. Trajectory calculations also provide essential guidelines for the construction of system components such as energy analyzers. In order to measure fluctuation-induced transport (ñ, φ̃, phase, k), the analyzers will have multiple slits. The distance of the apertures that gives reasonable distances of the sample volumes in the plasma was determined, and examples for sample volumes sizes and shapes, which determine the quality of the measurements, are presented. Another issue involving the quality and the understanding of HIBP measurements is ion beam attenuation. The trajectory code has been used to estimate the signal strength that can be expected from the 2 MeV HIBP. This work was supported by DOE.

Electric field studies of a 2 MeV electrostatic energy analyzer

An energy analyzer based on the Proca and Green parallel-plate design is being developed for use with the 2 MeV heavy ion beam probe on TEXT. In a departure from the conventional configuration, guard ring electrodes will not be used. Instead, a shaped top plate will provide for comparable, or improved, uniformity of the analyzer electric field region. To quantify this effect, and to characterize the electrostatic field, numerical solution methods have been utilized. Simulations have included effects of top plate shape, wire screens, vacuum chamber design, and dielectric support structures. The modeling has permitted us to design an analyzer electrode structure that is an integral part of a uniquely shaped vacuum vessel. The design electric field is 20 kV/cm with less than 1% error in uniformity within the parallel plate region. To examine the electric field structure experimentally, a quarter-scale prototype analyzer has been constructed and tested. The electric field characteristics are examined by varying the path of a heavy ion beam through the analyzer and examining the resulting analyzer performance. A simulated vacuum wall can be positioned to examine the effects of different vessel configurations and to determine the sensitivity of the analyzer to this boundary condition. The experimental results show excellent agreement with the numerically predicted fields and confirm the validity of the shaped top plate electrode concept.

Text-upgrade 2 MeV heavy ion beam probe (abstract)

A unique 2 MeV heavy ion beam probe diagnostic system, presently under construction, with two injection lines and two energy analyzers will be used to measure the space potential as well as density, electrostatic (and possibly magnetic) fluctuations, and average wave numbers in the TEXT upgrade tokamak. The capabilities of the 2 MeV beam include a good penetration of the TEXT-U magnetic fields (up to 2.2 T) and access to most of the plasma cross section (90%) including all null points (during divertor operations), the top, bottom, and outside edges. We plan to use parallel plate electrostatic energy analyzers which require that 400 kV be held on a large electrode across a 20 cm vacuum gap. Feasibility tests of such analyzers are under way. Progress of construction and testing of different parts of the system are reported. A description of the 2 MeV heavy ion beam probe system and a discussion on the measurements to be performed will be presented. This work was supported by DOE.

Damage production and annealing in ion-irradiated FCC metals

Abstract Damage production, radiation annealing and stage I recovery in some FCC metals irradiated with ∼ 1 MeV and ∼ 100 MeV ions near 10 K are studied using electrical resistivity measurements. For ∼ 1 MeV light and heavy ion irradiations, the fraction of stage I recovery and the damage efficiency decrease with the PKA median energy. For ∼ 100 MeV heavy ion irradiations, an anomalous reduction of stage I recovery and a large cross-section for subthreshold recombination are found in Ni, and an enhancement of the damage efficiency is found in Cu; they are interpreted as due to the electron excitation by irradiating ions and the subsequent energy transfer from excited electrons to lattice atoms. Simultaneous differential equations describing the production and radiation annealing of two or more types of defects are solved, where the respective defect concentration is expressed as a function of fluence.