Ion Beam Velocity Research Articles

Charge and Current Neutralization of an Ion-Beam Pulse Propagating in a Background Plasma along a Solenoidal Magnetic Field

The analytical studies show that the application of a small solenoidal magnetic field can drastically change the self-magnetic and self-electric fields of the beam pulse propagating in a background plasma. Theory predicts that when omega_{ce} approximately omega_{pe}beta_{b}, where omega_{ce} is the electron gyrofrequency, omega_{pe} is the electron plasma frequency, and beta_{b} is the ion-beam velocity relative to the speed of light, there is a sizable enhancement of the self-electric and self-magnetic fields due to the dynamo effect. Furthermore, the combined ion-beam-plasma system acts as a paramagnetic medium; i.e., the solenoidal magnetic field inside the beam pulse is enhanced.

Beam effect on electromagnetic ion-cyclotron waves with general loss – cone distribution function in an anisotropic plasma-particle aspect analysis

Abstract. The effect of upgoing ion beam and temperature anisotropy on the dispersion relation, growth rate, parallel and perpendicular resonant energies, and marginal instability of the electromagnetic ion cyclotron (EMIC) waves, with general loss-cone distribution function, in a low β homogeneous plasma, is discussed by investigating the trajectories of the charged particles. The whole plasma is considered to consist of resonant and non-resonant particles. The resonant particles participate in an energy exchange with the waves, whereas the non-resonant particles support the oscillatory motion of the waves. The effects of the steepness of the loss-cone distribution, ion beam velocity, with thermal anisotropy on resonant energy transferred, and the growth rate of the EMIC waves are discussed. It is found that the effect of the upgoing ion beam is to reduce the energy of transversely heated ions, whereas the thermal anisotropy acts as a source of free energy for the EMIC waves and enhances the growth rate. It is found that the EMIC wave emissions occur by extracting energy of perpendicularly heated ions in the presence of an upflowing ion beam and a steep loss-cone distribution function in the anisotropic magnetoplasma. The effect of the steepness of the loss-cone is also to enhance the growth rate of the EMIC waves. The results are interpreted for EMIC emissions in the auroral acceleration region.

In-flight emission of projectile Auger electrons from highly energetic heavy ions (20 MeV/u < E < 100 MeV/u) colliding with carbon foils

Highly energetic projectiles (20MeV/u<Ebeam<100MeV/u), which have been collisionally excited during penetration of thin solid foils, can deexcite by emission of Auger electrons. These in-flight emitted fast electrons are observed in the laboratory system with a velocity intermediate between vbeam (the ion beam velocity) and 2vbeam. Results obtained both at the Catania LNS superconducting cyclotron CS with 58Ni14+,19+ (23 and 45MeV/u) and at Ganil with 78Kr32+,34+ (64MeV/u) are presented. Absolute emission cross-sections and kinematic properties are discussed.

Determination of Plasma Flow Velocity by Mach Probe and Triple Probe with Correction by Laser-Induced Fluorescence in Unmagnetized Plasmas

Plasma flow velocity was measured by Mach probe (MP) and laser-induced fluorescence (LIF) methods in unmagnetized plasmas with supersonic ion beams. Since the ion gyro-radius was much larger than the probe radius, unmagnetized Mach probe theory was used to determine plasma flow in argon RF plasma with a weak magnetic field (<200 G). In order to determine flow velocities, the Mach probe is calibrated via LIF in the absence of the ion beam, where existing probe theories may be valid although they use different geometries (sphere and plane) and analyzing tools [particle-in-cell (PIC) and kinetic models]. For the comparison of the average plasma flow velocities by MP and LIF, the supersonic ion beam velocity was measured by LIF and then incorporated into a simple formula for average plasma velocity with provisions for background plasma density and beam-corrected electron temperature (Te) measured by a triple probe.

Effect of parallel electric field on electrostatic ion-cyclotron instability in anisotropic plasma in the presence of ion beam and general distribution function—Particle aspect analysis

Dispersion relation, resonant energy transferred, growth rate and marginal instability criteria for the electrostatic ion-cyclotron wave with general loss-cone distribution in low- β anisotropic, homogeneous plasma in the auroral acceleration region are discussed by investigating the trajectories of the charged particles. Effects of the parallel electric field, ion beam velocity, steepness of the loss-cone distribution and temperature anisotropy on resonant energy transferred and growth rate of the instability are discussed. It is found that the effect of the parallel electric field is to stabilize the wave and enhance the transverse acceleration of ions whereas the effect of steepness of loss-cone, ion beam velocity and the temperature anisotropy is to enhance the growth rate and decrease the transverse acceleration of ions. The steepness of the loss-cone also introduces a peak in the growth rate which shifts towards the lower side of the perpendicular wave number with the increasing steepness of the loss-cone.

Ion beam pulse neutralization by a background plasma in a solenoidal magnetic field

Ion beam pulse propagation through a background plasma in a solenoidal magnetic field has been studied analytically. The neutralization of the ion beam current by the plasma has been calculated using a fluid description for the electrons. This study is an extension of our previous studies of beam neutralization without an applied magnetic field. The high solenoidal magnetic field inhibits radial electron transport, and the electrons move primarily along the magnetic field lines. For high-intensity ion beam pulses propagating through a background plasma with pulse duration much longer than the electron plasma period, the quasi-neutrality condition holds, n e = n b + n p , where n e is the electron density, n b is the density of the ion beam pulse, and n p is the density of the background plasma ions (assumed unperturbed by the beam). For one-dimensional electron motion, the charge density continuity equation ∂ ρ / ∂ t + ∇ · j = 0 combined with the quasi-neutrality condition [ ρ = e ( n b + n p - n e ) = 0 ] yields j = 0 . Therefore, in the limit of a strong solenoidal magnetic field, the beam current is completely neutralized. Analytical studies show that the solenoidal magnetic field starts to influence the radial electron motion if ω ce ⩾ ω pe β (where ω ce = eB / mc is the electron gyrofrequency, ω pe is the electron plasma frequency, and β = V b / c is the ion beam velocity relative to the speed of light). This condition holds for relatively small magnetic fields. For example, for a 100 MeV, 1 kA Ne + ion beam ( β = 0.1 ) and a plasma density of 10 11 cm - 3 , B corresponds to a magnetic field of 100 G.

Generation mechanism of electrostatic waves in the upstream and shock transition regions of quasi‐parallel shocks

Primarily, one‐dimensional full‐particle electromagnetic simulations supplemented by a two‐dimensional simulation are performed to investigate the excitation processes of electrostatic waves in quasi‐parallel shocks. The characteristic waves are ion acoustic, ion beam‐mode, and upper‐hybrid waves. In the upstream region, only ion beam‐mode electrostatic waves are excited by the reflected ion beam running almost parallel to the ambient magnetic field. We find that the ion beam‐mode waves evolve into electrostatic solitary waves (ESW) for an appropriate ion beam velocity. The evolution of the ion beam‐mode to ESW is most clearly observed in the simulation when the ambient magnetic field is taken to be parallel to the ion beam direction. We confirm that the ion beam‐mode waves are excited only in the direction parallel to the ambient magnetic field. In the shock transition region (STR) the simulation results show that upper‐hybrid waves are excited on the upstream side of the STR by the reflected ion beam running almost perpendicular to the ambient magnetic field. In the STR region a large‐amplitude and quasi‐monochromatic oblique whistler wave is also excited. On the downstream side of the STR, ion acoustic waves are excited. The mechanism of the excitation of the ion acoustic wave is the current‐driven instability. This instability is generated by the velocity difference between ions and electrons due to electron acceleration in the shock potential. Of these three types of waves, the ion acoustic waves scatter electrons most effectively and contribute to the electron heating processes in the shock region.

Dust acoustic solitary waves and double layers in a dusty plasma with an arbitrary streaming ion beam

The effects of variable dust charge, dust temperature and an arbitrary streaming ion beam on small amplitude dust acoustic waves are investigated. It is found that both compressive and rarefactive solitons as well as double layers exist. There exists a critical ion beam velocity below which the ion beam is unable to generate solitons. Korteweg–de Vries (KdV) equations with third and fourth-order nonlinearity at the critical values are derived and the properties of dust acoustic solitary waves are discussed. In the vicinity of the critical values, KdV-type with mixed nonlinearity is obtained. The quite dense positive ion, the dust temperature, the ion beam density, mass ratio and temperature govern the existence of dust acoustic waves. The findings of this investigation may be useful in understanding laboratory plasma phenomena and astrophysical situations.

Numerical simulation of ion thruster-induced plasma dynamics — the model and initial results

Recently, there is a strong interest in ion thrusters as propulsion devices for interplanetary missions. Apart from their propulsive efficiency, the operation of ion thrusters in space constitutes a very interesting active plasma experiment, and the associated plasma physical dynamics are only poorly understood. We give an overview of the thruster-induced plasma environment and describe the numerical simulation with which we attempt to explore the main dynamical phenomena in this environment. The simulation is applied to a simplified ion thruster neutralization regime. Initial results for an injection velocity ratio η = ν e0 th /ν i0 = 1 between electron thermal velocity and ion beam velocity reveal the occurrence of an electrostatic shock wave that provides a complete thermalization of the beam plasma.

Neutron Production Characteristics and Emission Properties of Spherically Convergent Beam Fusion

Experimental results of spherical glow discharge for a portable neutron source are presented. An experimental device consisting of a 45-cm-diam, 31-cm-high stainless steel cylindrical chamber was constructed in which a spherical mesh-type 30-cm-diam anode was installed. A spherical grid cathode made of 1.2-mm-diam stainless steel wire was made into a 7-cm-diam open spherical grid. The system was maintained at a constant pressure of 1 to 15 mTorr by feeding hydrogen or deuterium gas. The visible and ultraviolet emissions from the device were measured using the spectroscopic method. Strong emission lines of hydrogen were observed, and all hydrogen lines were broadened, remarkably, by Doppler and/or Stark effects. From these data, beam ion velocity, electron density and temperature of the core plasma were estimated. Using deuterium gas, a steady-state neutron production rate of 104 s−1 was observed at a discharge of 40 kV, 2 mA. In the low-current region of several milliamperes, the neutron production rate was proportional to the discharge current to the power from ~1.1 to 1.4. The beam-background reactions were dominant in the measured range of voltage and current.

Isotope Shift Measurement Between He-like 12C and 13C Ions in 1s2s 3S1–1s2p 3P0,1,2 Transitions

To demonstrate isotope shift measurement for high-energy highly charged ion beams, we measured precisely the 1s2s 3S1–1s2p 3P0,1,2 transition energy of He-like 12C ion accelerated up to 0.9 MeV/u and 13C ion to 0.6 MeV/u. For the precision measurement, the uncertainty coming from the ambiguity in the absolute ion beam velocity was suppressed by means of that the resonance energy was measured by two laser beams which propagate in parallel and anti-parallel directions to the ion beam. As the results, an isotope shifts of these transitions were obtained with an accuracy of 10%.

Physics of energetic particle-driven instabilities in the STARTspherical tokamak

The recent use of neutral beam injection (NBI) in the UKAEA small tight aspect ratio tokamak (START) has provided the first opportunity to study experimentally the physics of energetic ions in spherical tokamak (ST) plasmas. In such devices the ratio of major radius to minor radius R0/a is of order unity. Several distinct classes of NBI-driven instability have been observed at frequencies up to 1 MHz during START discharges. These observations are described, and possible interpretations are given. Equilibrium data, corresponding to times of beam-driven wave activity, are used to compute continuous shear Alfvén spectra: toroidicity and high plasma beta give rise to wide spectral gaps, extending up to frequencies of several times the Alfvén gap frequency. In each of these gaps Alfvénic instabilities could, in principle, be driven by energetic ions. Chirping modes observed at high beta in this frequency range have bandwidths comparable to or greater than the gap widths. Instability drive in START is provided by beam ion pressure gradients (as in conventional tokamaks), and also by positive gradients in beam ion velocity distributions, which arise from velocity-dependent charge exchange losses. It is shown that fishbone-like bursts observed at a few tens of kHz can be attributed to internal kink mode excitation by passing beam ions, while narrow-band emission at several hundred kHz may be due to excitation of fast Alfvén (magnetosonic) eigenmodes. In the light of our understanding of energetic particle-driven instabilities in START, the possible existence of such instabilities in larger STs is discussed.

Effects of the ion-beam density and velocity on the excitation of multimode soliton

Multimode solitons are observed to be excited in an ion-beam–plasma system. But, the excitation of some mode solitons of these is found to be suppressed under a certain condition depending on the density and velocity of a low-energy ion beam, produced by the applied negative pulse. Furthermore, weak interaction between the slow-beam soliton and ion-acoustic soliton is also observed to cause small time lags in their trajectories on the distance–time plane.

Orientation of Na∗ atoms formed under grazing scattering at an Al surface

A study of the angular momentum orientation of excited Na∗ 3p atoms by grazing scattering of Na+ ions from an Al surface is presented. The coupled angular mode (CAM) method, previously used for the nonperturbative treatment of dynamic resonant electron-transfer in grazing atom-surface collisions [1,2], is used for the study of this polarization problem. Following the dynamical approach of Brako [3,4] density matrix elements are calculated within the 3p subspace of Na. A pronounced orientation of the orbital angular momentum perpendicular to the scattering plane is obtained. For the first time, a theoretical calculation has yielded a decrease of this atomic orientation with decreasing ion-beam velocities below 0.4 Bohr. Overall agreement of the theoretical results with experimental observations is found.

Observation of controlled intermittent chaos in ion-beam-plasma instabilities.

Under the modulation of the ion-beam velocity with a frequency close to the fundamental characteristic natural frequency of the system, the intermittent chaotic structure is observed in a well controlled manner in the ion-beam--plasma system. In the chaotic regime, the Lyapunov exponent is positive, and both the correlation dimension and the Lyapunov dimension are greater than 2.

The kinetic dust-acoustic instability in a magnetized dusty plasma

Using kinetic theory the dust-acoustic instability is investigated in a fully magnetized plasma consisting of stationary electrons, negatively charged, massive dust particles and a component of drifting ions. A detailed examination of the dependence of the frequency and growth rate of the instability on plasma parameters such as particle densities and temperatures, ion beam velocity and the strenth of the confining magnetic field is conducted.

On the Formation of Cup-like Ion Beam Distributions in the Plasma Sheet Boundary Layer

In the end of the 1970ies fast ion flows were discovered, jetting along the boundary of the plasma sheet (PSBL) in the Earth's magnetotail. Now, with the help of new technology devices on board of GALILEO and the GEOTAIL spacecraft, more and more exciting details of the three-dimensional beam velocity distributions are being discovered like, e.g., filaments and rings. In order to understand the origin of these structures and in order to use them for remote diagnostics of acceleration processes, we have derived a quasi-adiabatic theory of the non-linear dynamics of strong acceleration in two-dimensional current sheet fields. Together with the typical magnetotail velocity dispersion our approach reveals, in general, cup-like ion beam velocity distributions. In dependence on the accelerating current sheet electro-magnetic fields the cup-like ion beam velocity distributions may degenerate either to the well known lima-bean shape or to ring distributions. We illustrate our findings by test particle simulations of the beam velocity distribution functions and compare them with ring distributions, observed by GEOTAIL.

Beam‐driven acoustic solitary waves in the auroral acceleration region

The formation of ion acoustic solitary structures driven by electron and ion beams in the auroral acceleration region is studied using two‐dimensional electrostatic particle simulations. The beams are consistently present in regions of moderate potential drop (≤ 1 keV) where weak double layers have been observed on both the S3‐3 and Viking spacecraft. The presence of more than one ion species introduces the ion two‐stream instability besides the ion acoustic one into the system and modifies previous analysis and simulation results of solitary wave formation. Solitary structures form as a result of the microinstability development. The numerical simulation results show that positively peaked (ϕ &gt; 0) localized structures are formed in the system driven by a dense (nib ≈ nic ≈ ne/2) ion beam. The solitary waves move in the direction of the ion beam velocity. By contrast, negative potential solitary structures form when the ion beam density is reduced to 10 % (nib ≈ 0.1 ne) and electron drift relative to background ions is sustained by an applied electric field. In this case, solitary waves drift downward at subsonic speeds relative to the background ions, which may carry the localized pulses upward. Evolving solitary waves do not carry any significant net potential drop and therefore cannot contribute much to the auroral particle acceleration. They are found to be a consequence of the larger‐scale V‐shaped potential distribution in the auroral region.

Spontaneous and deflected drift-trajectories in orthogonal acceleration time-of-flight mass spectrometry

Orthogonal acceleration is a method for gating ions from an ion beam into a time-of-flight (TOF) mass spectrometer. The technique involves a pulsed electric field to apply acceleration directed orthogonally to an ion beam. This approach is useful for coupling continuous ion sources to TOF mass analyzers. Most instruments of this type, which have been described in the literature, use steering electrodes after the orthogonal acceleration step. Those velocity components of ions originating from the ion beam velocity are minimized so that the deflected drift-trajectory is parallel to a transverse flight tube. In an alterantive geometry the ion beam velocity is conserved and the drift-trajectory after the orthogonal acceleration step is spontaneous. The differences between the space-time focusing ability with spontaneous and deflected drift-trajectories are discussed and investigated. Trajectory calculations indicate that deflection fields placed after the orthogonal acceleration step distort the ion packet because, in this geometry, the flight-time to the detector is dependent on the position that the ions enter the steering optics. Increasing the duty-cycle efficiency by sampling longer sections of the continuous ion beam leads to a degradation of resolving power. Employing a spontaneous drift-trajectory after orthogonal acceleration provides the advantage that the arrival time spread for isobaric ions is, in principle, independent of the length of the ion beam sampled. The major implication of these findings is that simultaneously optimized sensitivity and resolving power may not be achievable with the deflected drift-trajectory instruments. The calculations are in agreement with results from the published data of a number of groups who have built instruments based on the orthogonal acceleration principle.

Solitons in a magnetized ion-beam plasma system

The formation of ion-acoustic solitary waves in a magnetized plasma with stationary ions and beam ions together with inertia-less electrons is investigated. The generation of waves in a plane is assumed to be one-dimensional, in a direction inclined at an angle θ to the direction of the magnetic field, with constant drift velocity of the ion beam. Remarkably, the amplitudes of the solitons are found to attain a maximum value at a particular beam-ion velocity γ, and then decrease slightly and remain almost constant for higher γ. The width of the waves is large at small y for small beam-ion density Nb, but it attains a constant minimum value at a particular value of γ. The amplitude decreases sharply to zero with decreasing y, whereas it remains almost constantly high for larger y. It is observed that as a wave approaches the direction of the magnetic field, its amplitude increases to a constant maximum value, which is larger for higher beam-ion velocities.