Ion Beam Mode Research Articles

MC design and FIB preparation of a YSZ biochemical material microstructure

Aiming at the difficulty of traditional machining of Y2O3–ZrO2 (YSZ) inert ceramic materials, a different method using focused ion beam to selectively create nanoscale microscale structures on the surface of materials was proposed. The sputtering yield, surface damage, and the energy loss of YSZ materials was investigated using the SRIM software using the Monte Carlo method. It is shown that the sputtering yield increases with ion energy in the range 0–30 keV, reaching a maximum of 9.4 atoms/ion at 30 keV. At an ion beam voltage of 30 keV, the most severe damage to the material is 8 mm on the surface. At the same time, the main forms of energy loss in the treatment are phonon energy loss and ionization energy loss, of which phonon energy loss due to the recoil atoms is the largest. In addition, we continue to perform focused ion beam processing experiments on YSZ materials, combining previous MC modeling to optimize different operating conditions such as ion beam, voltage and processing mode. The optimized processing parameters are 30 keV and 2.5 nA. It is shown that the quality of the deep grooves gradually improves with decreasing ion beam current at the same ion beam voltage. However, an excessively small ion beam current leads to an excessively large depth of the deep grooves and lengthy processing times.

Observation of multi-mode ion waves in electron cyclotron resonance plasma

In this paper, ion waves were experimentally investigated in a microwave electron cyclotron resonance plasma. By applying a ramp voltage to a negatively biased excitation grid, multimode ion waves were excited. It was found through the time-of-flight method that the velocities of the excited ion waves are independent of the excitation signals, suggesting that the waves are eigenmodes of the plasma. Plasma potential, electron temperature, and electron density decrease from the source chamber to the target chamber, which establishes a spatial electrostatic field for ion acceleration. There exists a broad and multimodal ion distribution function along the magnetic field axis, which was observed using a retarding-field-energy-analyzer. Applying the model of an ion-beam-background-plasma system, three kinds of ion waves were identified as fast and slow ion-beam modes and an ion acoustic mode. In addition, the dependence of the amplitudes of the excited ion waves on the rise time of the ramp signal was presented, which is correlated with the difference in the times that the beam ions and background ions take to pass through the plasma sheath.

Co-excitation of normal modes and burst ion signal in an ion-beam–plasma system

The co-excitation of plasma normal modes and a pseudo-mode (burst-ion signal) in a beam–plasma system containing a stationary ion beam is experimentally investigated in a double-plasma device. The ion waves are excited by applying a ramp voltage to an excitation grid (rather than separation grid) immersed in the beam–plasma system. By studying the dependence of the phase velocities of the excited signals on the characteristics of the ramp signal and on the ion-beam velocity, four kinds of coexisting waves can be identified, i.e., a fast and a slow ion-beam modes, an ion-acoustic mode, and the burst-ion signal, respectively.

Large amplitude solitary waves in ion-beam plasmas with charged dust impurities

The nonlinear propagation of large amplitude dust ion-acoustic (DIA) solitary waves (SWs) in an ion-beam plasma with stationary charged dusts is investigated. For typical plasma parameters relevant for experiments [Y. Nakamura and K. Komatsuda, J. Plasma Phys. 60, 69 (1998)], when the beam speed is larger than the DIA speed (νb0 ≳ 1.7cs), three stable waves, namely, the “fast” and “slow” ion-beam modes and the plasma DIA wave, are shown to exist. These modes can propagate as SWs in the beam plasmas. However, in the other regime (cs < νb0 < 1.7cs), one of the beam modes when coupled to the DIA mode may become unstable. The SWs with positive (negative) potential may exist when the difference of the nonlinear wave speed (M) and the beam speed is such that 1.2 ≲ M − νb0 ≲ 1.6 (M − νb0 ≳ 1.6). Furthermore, for real density perturbations, the wave potential ( > 0) is found to be limited by a critical value which typically depends on M, νb0 as well as the ion/beam temperature. The conditions for the existence of DIA solitons are obtained, and their properties are analyzed numerically in terms of the system parameters. While the system supports both the compressive and rarefactive large amplitude SWs, the small amplitude solitons exist only of the compressive type. The theoretical results may be useful for observation of soliton excitations in laboratory ion-beam driven plasmas as well as in space plasmas where the charged dusts play as impurities.

Identification of silicate and carbonaceous presolar grains by SIMS in the type-3 enstatite chondrite ALHA81189

An isotope ratio imaging technique using the HokuDai isotope microscope system has been applied to in situ survey for presolar grains in the type-3 enstatite chondrite ALHA81189. Rastered and static ion beam were used for primary beam. Lateral resolution of the isotope image was achieved to be 0.4 μm for static ion beam mode and to be 0.6 μm for rastered ion beam mode. As a result, the abundances of presolar grains are 150–200% larger under the static ion beam mode than under the rastered ion beam mode. Development of image processing introducing isotopography of 32S −, 24Mg 16O − and 56Fe − succeeded to increase efficiency of presolar grain characterization. Using the static ion beam and introducing appropriate isotopography were very useful methods of in situ characterization of presolar grains in meteorites.

Effect of burst ions on the excitation of ion-acoustic solitons in a drifting plasma

The characteristics of fast burst ions and ion-acoustic solitons in a drifting plasma, as well as their interaction, are investigated experimentally. It is shown that the soliton evolves from the normal fast ion-beam mode excited locally in the presheath region of an excitation grid. The burst ions are created by applying a positive ramp voltage to the grid. Adjusting the rise time and amplitude of the ramp signal can lead to significant changes in the average speed of the burst ions, resulting in strong interaction (inverse Landau damping) between the burst ions and the soliton. The resonance conditions for solitons propagating along and against the plasma flow are shown to be different, since the soliton speed depends on the propagation direction.

Generation of filamentary structures by beam-plasma interaction

The previous simulations by Wang and Lin [Phys. Plasmas. 10, 3528, (2003)] showed that filaments, frequently observed in space plasmas, can form via the interaction between an ion beam and a background plasma. In this study, the physical mechanism for the generation of the filaments is investigated by a two-dimensional hybrid simulation, in which a field-aligned ion beam with relative beam density nb=0.1 and beam velocity Vb=10VA is initiated in a uniform plasma. Right-hand nonresonant ion beam modes, consistent with the linear theory, are found to be dominant in the linear stage of the beam-plasma interaction. In the later nonlinear stage, the nonresonant modes decay and the resonant modes grow through a nonlinear wave coupling. The interaction among the resonant modes leads to the formation of filamentary structures, which are the field-aligned structures (k⊥B) of magnetic field B, density, and temperature in the final stage. The filaments are nonlinearly generated in a prey-predator fashion by the parallel and oblique resonant ion beam modes, which meanwhile evolve into two types of shear Alfvén modes, with one mainly propagating along the background field B0 and the other obliquely propagating. The filamentary structures are found to be phase standing in the plasma frame, but their amplitude oscillates with time. In the dominant filament mode, fluctuations in the background ion density, background ion temperature, and beam density are in phase with the fluctuations in B, whereas the significantly enhanced beam temperature is antiphase with B. It is found that the filaments are produced by the interaction of at least two ion beam modes with comparable amplitudes, not by only one single mode, thus their generation mechanism is different from other mechanisms such as the stimulated excitation by the decay of an Alfvén wave.

Electron cyclotron microinstability in the foot of a perpendicular shock: A self-consistent PIC simulation

We have performed one-dimensional full particle simulations of perpendicular shocks and found that an electron cyclotron microinstability can develop in the foot during the self-reformation phase of low β i supercritical shocks. The instability is excited by the beam of reflected ions interacting with the incoming electrons. It exhibits a rapid growth, and propagates along the shock normal towards upstream. This instability, which does not require high Mach number, has a frequency comparable to the electron cyclotron frequency and a wavelength shorter than the electron inertia length. It basically results from the coupling of electron Bernstein waves with an ion beam mode carried by the reflected ions. Dispersion properties in the foot are analysed. We discuss the effects of varying parameters, in particular as the fake ion-to-electron mass ratio used in the simulations converges to more realistic values. Comparison with other microinstabilities evidenced in recent full particle simulations of shocks is outlined.

Graphical analysis of electron inertia induced acoustic instability

Recently, the practical significance of the asymptotic limit of me∕mi→0 for electron density distribution has been judged in a two-component plasma system with drifting ions. It is reported that in the presence of drifting ions with drift speed exceeding the ion acoustic wave speed, the electron inertial delay effect facilitates the resonance coupling of the usual fluid ion acoustic mode with the ion-beam mode. In this contribution the same instability is analyzed by graphical and numerical methods. This is to note that the obtained dispersion relation differs from those of the other known normal modes of low frequency ion plasma oscillations and waves. This is due to consideration of electron inertial delay in derivation of the dispersion relation of the ion acoustic wave fluctuations. Numerical calculations of the dispersion relation and wave energy are carried out to depict the graphical appearance of poles and positive-negative enegy modes. It is found that the electron inertia induced ion acoustic wave instability arises out of linear resonance coupling between the negative and positive energy modes. Characterization of the resonance nature of the instability in Mach number space for different wave numbers of the ion acoustic mode is presented.

Current status of JAERI spallation target material program

In the joint project of spallation neutron source between JAERI and KEK, material technology has been developed for the mercury target in the neutron source facility, the lead–bismuth target in the transmutation test facility, superconducting accelerator, post-irradiation examination and the ion beam test. Design of target system is progressing for the mercury spallation target: a pressure test of moderator, an impacting test in mercury and a corrosion test have been carried out. For nuclear transmutation with ADS an engineering facility is proposed. A material corrosion test loop is built-up and SS316 and F82H steels are to be tested in a flowing Pb–Bi. Fracture toughness of superconducting cavity material was found to be considerably large at 4 K. Irradiated samples at SINQ are to be transported to JAERI Hot Laboratory. For simulating radiation damage small disk specimens were irradiated in single, dual and triple ion beam modes.

Vacuum arc metal plasma production and the transition of processing mode from metal ion beam to dc metal plasma immersion

The vacuum arc provides a straightforward method for the efficient production of dense metal plasma. The plasma so formed can be utilized more-or-less ‘as-is’, or with macroparticle filtering, for the deposition of films of many different kinds. More advanced techniques involve substrate pulse-biasing to achieve a metal plasma immersion processing mode, or the vacuum arc plasma source can be embodied within an ion source configuration for the formation of energetic metal ion beams for carrying out ion implantation. Not inconsequentially, the vacuum arc metal plasma has an innate high ion drift velocity (ion drift speed greater than the ion sound speed), a plasma feature that leads to some novel and important consequences — a negatively-biased substrate located in the plasma stream can maintain unexpectedly high voltages on an essentially dc basis, and an ion source with ‘conventionally poor’ extractor design can provide a kind of plasma immersion ion implantation mode of operation. As the ion source operating parameters are varied, there can in fact be a smooth transition between these two modes — a plasma immersion processing mode and an energetic ion beam processing mode. The metal ion beam mode of operation and the plasma immersion mode of operation are closely related because of the plasma drift. Here, vacuum arc generation of metal plasma is summarized, and a brief review of ion source and plasma immersion modes presented. The significance of high plasma drift as a mechanism that can lead to a dc (or, at least, long-pulse) mode of plasma immersion ion implantation is outlined.

Triple ion beam studies of radiation damage in 9Cr–2WVTa ferritic/martensitic steel for a high power spallation neutron source

To simulate radiation damage under a future Spallation Neutron Source (SNS) environment, irradiation experiments were conducted on a candidate 9Cr–2WVTa ferritic/martensitic steel using the Triple Ion Facility (TIF) at ORNL. Irradiation was conducted in single, dual and triple ion beam modes using 3.5 MeV Fe ++, 360 keV He +, and 180 keV H + at 80°C, 200°C and 350°C. These irradiations produced various defects comprising black dots, dislocation loops, line dislocations, and gas bubbles, which led to hardening. The largest increase in hardness, over 63%, was observed after 50 dpa for triple beam irradiation conditions, revealing that both He and H are augmenting the hardening. Hardness increased less than 30% after 30 dpa at 200°C by triple beams, compatible with neutron irradiation data from previous work which showed about a 30% increase in yield strength after 27.2 dpa at 365°C. However, the very large concentrations of gas bubbles in the matrix and on lath and grain boundaries after these simulated SNS irradiations make predictions of fracture behavior from fission reactor irradiations to spallation target conditions inadvisable.

Wave excitation in a modified double plasma device

A modified double plasma (MDP) device is newly developed and shown to be useful for basic plasma wave experiments. Further, the mechanism of wave excitation in the MDP device is experimentally clarified. From the results the peculiarity of the device is found, that ion-acoustic waves can be excited in plasmas essentially freely from the effects of stationary beam ions and other modes, such as ion-beam modes as far as linear waves are concerned. For nonlinear waves, however, ion-acoustic solitons or shocks with reflected ions ahead and slower wave-like signals behind are possibly excited just as in a conventional DP device.

Nonlinear modulation of ion plasma waves via parametric processes

Nonlinear modulation of the “slow” ion-beam modes in a beam-plasma system is experimentally shown to occur above a threshold of wave amplitude and to progress during propagation. The threshold is found to change depending on the wave frequency at a fixed plasma density and on the plasma density at a fixed frequency. The wave modulation is also studied by means of analysis of frequency spectra. The result reveals that the frequencies of the lower or upper sidebands, generated as a result of the wave–wave interaction, vary roughly in proportion to the ion plasma frequency fpi, when the plasma density is changed. Finally, on the basis of experimental data obtained here, the nonlinear modulation of the wave is tentatively interpreted to result from the parametric process, based on the three wave interaction satisfying relations ω0=±ω1+ω2 and k0=±k1+k2.

Ion energy determination for r.f. plasma and ion beam using a multigrid retarding field analyser

The ion energy distribution of a capacitively coupled r.f. (13.56 MHz) plasma and ion beam source has been measured. The extraction optics consists of two stainless steel grids. The source has been operated in two different configurations, either with or without extraction optics. In the latter case the discharge serves only as a plasma source to be used directly or as remote plasma. For measurements of ion energy in the plasma mode a four-grid retarding field analyser (RFA) was used. For analysis of ion energy in the ion beam mode a slightly different RFA was used, because the retarding voltage here is higher, corresponding to extraction voltages of several hundred volts. In the plasma mode, all distributions exhibit a single-peak structure with a low-energy tail. With increasing pressure from 4 × 10 −2 to 4 Pa the distribution width shows an increase from 1.5 to 4.5 eV, whereas the average ion energy decreases from 48 to 17.4 eV. In the ion beam mode, the ion energy distribution is studied as a function of the r.f. power and pressure.

Two‐dimensional simulations of magnetic pulsations upstream of the Earth's bow shock

The development of turbulence upstream of the quasi‐parallel portion of the Earth's bow shock is investigated using two‐dimensional hybrid simulations involving the injection of a very hot ion beam against a cold incident ion flow. Initially, waves are produced in the right‐hand resonant ion beam mode and with wave vectors mainly parallel to the ambient magnetic field B0 as expected in linear theory. The waves attempt to propagate upstream but are convected back toward the shock by the incident flow and strongly grow in amplitude as they encounter larger beam densities. Wave growth is associated with reduction of both incident and beam ion bulk velocities. Differential slowing of the incident flow between the different wave fronts and, when the angle θBn between B0 and the shock normal n is non zero, along the fronts themselves, leads to wave front refraction parallel to the shock and fragmentation into smaller structures. Simultaneously, strong scattering by the waves generates beam ion clumps containing a significant fraction of ions with velocities antiparallel to the beam bulk velocity, which enables the destabilization of the left‐hand resonant ion beam mode. The beam ions ultimately form a diffuse distribution whose density ratio relative to the solar wind is a few percents in average, but increases up to about 20% in the immediate vicinity of the shock. These processes result in the formation of magnetic pulsations whose extension parallel and perpendicular to n is typically 15 and a few tens of ion inertial lengths, respectively. These structures can reach total amplitudes δB of 3 to 4 B0, and exhibit most of the time a left‐handed polarization in the plasma rest frame, in agreement with spacecraft observations upstream of the Earth's bow shock. The simulations show that pulsations induce slowing and moderate heating of the incident flow and play an active role in the quasi‐parallel shock transition.

Observation of Wave-Breaking into Packets in Beam-Plasma Systems

Breaking of slow ion-beam modes into wave packets in ion-beam-plasma systems is experimentally studied. When pump waves of the mode with a frequency around 200 kHz have amplitudes larger than a critical one, wave-breaking into many packets is observed to start at the axial position x ≃9 cm, and the packet amplitudes rapidly grow with increasing x .

Large-amplitude pulse response at the plasma boundary in an ion-beam system.

The reflection and transmission of a plane ion-acoustic soliton from a steep density gradient in front of a sheath have been investigated experimentally in an ion pulse beam system. An incident pulse tunnels through the space-charge sheath area without time delay and separates into three pulses at the plasma-sheath boundary. These pulses consist of a reflected and two transmitted pulses. One of them is a pulse of a fast ion-beam mode, while the others are ion-acoustic waves. The model for interpreting the phenomena is discussed.

Results of an experimental study of the properties of ion-beam modes found in a double plasma device containing a hemispherical separating screen

Ion-beam modes have been generated in a double plasma device containing argon in which the driver and target plasmas were separated by a hemispherical screen biased negatively with respect to both plasmas. Making the driver plasma positive with respect to the target plasma resulted in the formation of an ion beam flowing from the driver plasma to the target plasma and causing the formation of a focal region in the target plasma. Both single pulses and pulse trains were excited in the target plasma by application of positive voltage pulses and/or sine waves to the hemispherical grid. Detection of these modes was accomplished using a positively biased spherical probe capable of axial and rotational movement. The wave amplitude and the phase velocity along the axis of the target plasma were measured over a distance of more than two hemispherical grid radii. Since no theoretical treatments have as yet been published for the hemispherical case, the measured values have been compared with theoretical values for a spherical separating screen.

On the origin of short large‐amplitude magnetic structures upstream of quasi‐parallel collisionless shocks

In order to model the development of the turbulence upstream of quasi‐parallel shocks, one‐dimensional hybrid simulations have been performed of the injection of a very hot ion population into a cold incident flow. ULF electromagnetic waves are initially generated in the right‐hand resonant ion beam mode. As these waves are convected to the injection source and encounter larger beam densities, they grow in amplitude and scatter the beam ions. Beam ion clumps characterized by distributions with a significant fraction of ions having velocities antiparallel to the beam bulk velocity are generated, and destabilize the left‐hand resonant ion beam mode. This process enables the formation of enhanced magnetic field structures which, like the short large‐amplitude magnetic structures (SLAMS) observed upstream of the quasi‐parallel Earth's bow shock, show scale lengths smaller than the ULF waves wavelength, have magnetic amplitudes up to a few times the ambient magnetic field, are left‐hand polarized in the plasma rest frame, and often possess attached whistler waves.