Ion Beam Velocity Research Articles

Laser spectroscopy of highly charged ions at the storage ring CSRe: Schottky-based spectroscopic investigation and XUV fluorescence detector development

Laser spectroscopy stands out as a powerful tool to investigate atomic and nuclear properties and also test fundamental theories by precisely measuring the energy levels in highly charged ions. In this work, the fine-structure splitting 1s22s2S1/2−1s22p2P1/2 transition in lithium-like 16O5+ has been investigated in a laser spectroscopy experiment at the heavy-ion storage ring CSRe. The excitation resonance of the tunable narrowband UV laser and the ions was observed using a Schottky resonator with very high sensitivity. The experimental uncertainties including the ion beam velocity determination, the space charge effects, laser wavelength calibration, and angular misalignment between the laser and ion beam were analyzed, and the 2S1/2−2P1/2 transition wavelength was determined to be λ0= 103.45(38) nm. The primary source of experimental uncertainty arises from the inaccurate measurement of the high voltage applied on the electron cooler and therewith the ion beam velocity at the CSRe. In order to solve this problem, a high-precision divider to precisely measure the high-voltage of the electron cooler is under construction, which is expected to improve the present experimental accuracy by three orders of magnitude. In addition, an XUV optical detector equipped with an off-axis parabolic mirror has been developed and installed at the CSRe for the investigation of slow dipole-forbidden transitions in highly charged ions, such as hyperfine splitting and M1 transitions. The experimental studies presented here pave the way for future laser spectroscopy experiments at the CSRe as well as at the future larger-scale scientific facility HIAF in China.

The role of charge-exchange processes in probing hydrogen plasma with a heavy ion beam

Charge-changing processes of low-charged ions, used in hydrogen plasma probing by the heavy ion beam probe method, are considered. Along with the ionization of beam ions by plasma electrons and protons, the charge-exchange processes of ions on H atoms and protons are also studied. It is shown that charge exchange of beam ions on plasma protons and H atoms, which is rarely taken into account, plays an important role in beam–plasma interaction. New data on the cross sections and rates of ionization and charge-exchange processes are presented for Tl+ and Tl2+ ions, which are frequently used for plasma diagnostics. Calculations are performed for hydrogen plasma temperatures Te = 1 eV–10 keV and densities Ne = 1012–1014 cm−3 at relatively low and high ion-beam velocities vb = 0.2 and 1.0 a.u., respectively. Special attention is paid to the determination of the electron temperatures at which the charge-exchange processes on H atoms and protons are important. Multiple ionization of beam ions by plasma electrons and protons is briefly discussed.

Hybrid Simulation of Proton Cyclotron Waves Upstream of Mars Generated by Pickup Ion Beam Distribution

AbstractLinear instability analysis as well as a corresponding two‐dimensional hybrid simulation are performed to examine the excitation of the proton cyclotron waves observed upstream of Mars. The waves are believed to be excited by the pickup ions produced from the ionization of the Martian hydrogen exosphere. And previous statistical analysis of wave observations suggested that the waves are mostly related to pickup ion beam velocity distributions. While earlier linear instability analysis of pickup ion beam distributions has mainly been focused on the parallel unstable modes, our analysis reveals that the maximum growth rate occurs at very oblique propagation. The corresponding hybrid simulation confirms the linear analysis results and further demonstrates that the pickup ions are scattered toward an isotropic shell velocity distribution by the waves excited. Interestingly, the waves at oblique propagation gradually damp out and the system is eventually dominated by waves of quasi‐parallel propagation.

Towards an Intrinsic Doppler Correction for X-ray Spectroscopy of Stored Ions at CRYRING@ESR

We report on a new experimental approach for the Doppler correction of X-rays emitted by heavy ions, using novel metallic magnetic calorimeter detectors which uniquely combine a high spectral resolution with a broad bandwidth acceptance. The measurement was carried out at the electron cooler of CRYRING@ESR at GSI, Darmstadt, Germany. The X-ray emission associated with the radiative recombination of cooler electrons and stored hydrogen-like uranium ions was investigated using two novel microcalorimeter detectors positioned under 0∘ and 180∘ with respect to the ion beam axis. This new experimental setup allowed the investigation of the region of the N, M → L transitions in helium-like uranium with a spectral resolution unmatched by previous studies using conventional semiconductor X-ray detectors. When assuming that the rest-frame energy of at least a few of the recorded transitions is well-known from theory or experiments, a precise measurement of the Doppler shifted line positions in the laboratory system can be used to determine the ion beam velocity using only spectral information. The spectral resolution achievable with microcalorimeter detectors should, for the first time, allow intrinsic Doppler correction to be performed for the precision X-ray spectroscopy of stored heavy ions. A comparison with data from a previous experiment at the ESR electron cooler, as well as the conventional method of conducting Doppler correction using electron cooler parameters, will be discussed.

ЭКСПЕРИМЕНТАЛЬНОГО ИССЛЕДОВАНИЯ ПРОТОТИПА ИОННОГО ДВИГАТЕЛЯ ВРЕМЯПРОЛЕТНЫМ МЕТОДОМ

The article presents the results of experimental studies of the resonator ion thruster by the timeof-flight method in order to determine the accelerating structural elements. Four assembly variants were investigated: the outflow of ions from a magnetic cell; the outflow of ions from a magnetic cell with an installed core; the outflow of ions from a magnetic cell with an installed core and the side wall of the resonator; the outflow of ions from a magnetic cell with an installed core and the side wall of the resonator with a mesh cover. The energy consumption of the magnetic cell was 5.6 W, and the ion beam velocity at 11 Pa was no more than 7 m/s. In the assembly according to the second variant, the power consumption was 6.6 W at a pressure of 11 Pa and a speed of no more than 30 m/s. The power consumption for the third and fourth assembly variants was 6 watts, and the ion beam velocity at 11 Pa was no more than 48 m/s.

Determination of the ion beam velocity of an accelerator two-gap ion thruster

The article is devoted to the measurement of the ion beam velocity of an accelerator two-gap ion thruster. A theoretical representation of the physical process of capturing charged particles using a cylindrical sensing element is given. A schematic diagram and a printed circuit board for detecting an accelerated ion beam have been developed. The expression for calculating the signal current of the sensing element is defined. A condition for capturing charged particles using the critical mobility of charges is formulated.

Subshell contributions to electron capture into the continuum in MeV/u collisions of deuterons with multielectron targets

The process of the capture of a target electron into the projectile continuum (ECC) is investigated both experimentally and theoretically for collisions of 1.25--6.00 MeV deuterons with multielectron gas targets. Double-differential cross sections (DDCS), ${d}^{2}\ensuremath{\sigma}/d\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}dE$, of the ECC cusp-shaped electron peak involving He, Ne, and Ar gas targets were measured at the emission angle of zero degrees with respect to the ion-beam velocity. Corresponding DDCS calculations, obtained using continuum distorted-wave (CDW) and continuum distorted-wave eikonal initial-state (CDW-EIS) theories, were critically compared to the measurements. The role of each atomic subshell of the multielectron Ne and Ar targets is examined employing the CDW-EIS theory with numerical target wave functions, which is found to best agree with the measurements.

Kinetic Alfvén Waves in Space Plasma Environment with κ-electrons

Abstract A resonant instability of kinetic Alfvén waves (KAWs) driven by ion beam is discussed through a theoretical model encompassing Maxwellian background ions and beam ions and non-Maxwellian κ-electrons. The ion beam velocity alone as a source is able to excite the KAWs up to a significant growth. The non-Maxwellian parameter κ impedes the growth of KAWs by restricting the wave unstable region. The effects of other plasma parameters such as propagation angle, temperature of the plasma species, and ion plasma beta on the excitation of KAWs are also examined. The present model can generate waves with frequencies in the range of ≈6.6–51.2 mHz, which are relevant to explaining the observed ultralow frequency waves at auroral ionospheric altitudes. Theoretical model predictions will also be applicable to other planetary environments where ion beams and non-Maxwellian κ-electrons are present.

Ion Acoustic Shocks in a Weakly Relativistic Ion-Beam Degenerate Magnetoplasma

A theoretical investigation is carried out to study the propagation properties of ion acoustic shocks in a plasma comprising of positive inertial ions, weakly relativistic ion beam and trapped electrons in the presence of a quantizing magnetic field. By using the reductive perturbation technique, the Korteweg–de Vries-Burgers (KdVB) equation and oscillatory shocks solution are derived. The characteristics of such kinds of shock waves are examined and discussed in detail under suitable conditions for different physical parameters. The strength of the magnetic field, ion beam concentration and ion-beam streaming velocity have a great influence on the amplitude and width of the shock waves and oscillatory shocks. The results may be useful to study the characteristics of ion acoustic shock waves in dense astrophysical regions such as neutron stars.

Ion Acoustic Cnoidal Waves in Ion-Beam Dense Plasma in the Presence of Quantizing Magnetic Field

A study of propagation properties of ion-acoustic (IA) cnoidal waves in a magnetized degenerate quantum plasma comprising of inertial positive ions, weakly relativistic ion beam, and trapped electrons in the presence of quantizing magnetic field has been presented. The reductive perturbation technique is adopted to derive the Korteweg–de Vries (KdV)-type equation. Furthermore, the cnoidal wave solution of the KdV-type equation is obtained by using the Sagdeev pseudopotential method. Only positive potential IA cnoidal waves are evolved. The combined effects of ion-beam concentration, ion-beam velocity, quantizing magnetic field, and the temperature degeneracy of trapped electrons on the different characteristics of the IA cnoidal waves have been analyzed. The results of our present investigation may be useful to study the characteristics of IA cnoidal waves in dense astrophysical regions, such as white dwarfs.

High frequency Alfvén eigenmodes detected with ion-cyclotron-emission diagnostics during NBI and ICRF heated plasmas on the ASDEX Upgrade tokamak

The paper presents the first reported observation of high frequency Alfvén eigenmode excitation on the ASDEX Upgrade tokamak. The mode is driven in a novel way using radio frequency (RF) wave acceleration of either beam-injected deuterium ions or thermal He-3 minority ions in a three-ion heating scenario. In the case of beam ion acceleration, the instability only appears during deuteron acceleration at the third beam ion cyclotron harmonic (wave frequency ω = 3ΩD where ΩD is the deuterium cyclotron frequency), as the mode is not detected during the more commonly used second harmonic/minority heating scenario or in the absence of beam-injected ions. The mode frequency is around 0.6–0.7ΩD, where ΩD is evaluated in the low-field side plasma edge, and tracks the magnetic field B and the edge plasma electron density ne via the Alfvénic relation ω ∼ B ne −1/2. The mode does not appear as a single frequency wave but as a bundle of closely spaced (in frequency) sub-modes. When the parallel beam ion velocity component is increased, the sub-mode frequency spacing is observed to decrease, possibly due to a change in the eigenmode structure. Under certain conditions, typically in discharges with a relatively low plasma current, IP < 0.7 MA, the mode appears to be driven directly by sub-Alfvénic deuterium beam ions. Absolute measurements of the mode amplitude show that at least 1% of the beam-injected power is transferred non-collisionally to the instability. While this is too low for practical alpha-channeling applications, discharges are planned with the aim of increasing the level of power transferred non-collisionally between fast ions and the instability.

Nonresonant Instability of Kinetic Alfvén Waves with κ-electrons

Abstract A nonresonant instability of kinetic Alfvén waves (KAWs) is studied in a three-component plasma system consisting of background cold ions, an ion beam, and hot electrons with a κ-distribution. The nonresonant KAW instability is produced by the combined sources of ion beam and velocity shear. It is found that the wave excitation by velocity shear alone will give rise to purely growing KAWs, whereas the ion beam velocity alone as a source cannot excite the waves for the considered plasma parameters. It is also observed that the combined sources of ion beam and velocity shear can excite the KAWs in nonresonant instability with finite wave frequency (the mode is not a purely growing mode). Also note that κ-electrons restrict the wave propagation very close to 90°, whereas the Maxwellian electrons permit the wave to propagate a few degrees away from 90°. It is inferred that the presence of κ-electrons shrinks the wave-unstable region of a KAW’s nonresonant instability. The coupling between KAWs and ion-acoustic waves occurs at a lower value of β i for Maxwellian electrons as compared to κ-electrons.

Mitigation of multispecies Weibel instability in a finite non-neutral magnetized beam-plasma system.

Compressing and charge neutralization of the heavy-ion beam in an inertial fusion reactor are considered as pivotal processes for increasing the energy gain. For this purpose, the ion beam is usually transported through the plasma channel so that multispecies Weibel instability can grow in this system. Recently, a small solenoidal magnetic field has been added to this method to have additional control of these processes. On the other hand, charge and current may not be completely neutralized in this transport; as a result, the fractional charge and current neutralization can affect the growth rate of this instability. In this work, the dispersion equation has been obtained in cylindrical, cold, magnetized, non-neutral plasma in the macroscopic fluid frame. Numerical results show that if the electron cyclotron frequency of the background plasma normalized by plasma frequency is larger than the ion beam velocity normalized by the speed of light, as well as the current fraction being smaller than 1/2, the eigenmodes of multispecies Weibel instability can be completely stabilized. Moreover, these results are valid when the percent deviation from the charge-neutral state is positive. In the negative regime of percent deviation, the instability increases drastically so that the system can be completely unstable only for more than 2%. Therefore, selecting the radius of the ion beam smaller than the electron skin depth of the plasma and the beam pulse duration much longer than the plasma oscillation time are proposed for quenching of this instability.

Obliquely propagating quantum solitary waves in quantum‐magnetized plasma with ultra‐relativistic degenerate electrons and positrons

AbstractThe oblique propagation of the quantum electrostatic solitary waves in magnetized relativistic quantum plasma is investigated using the quantum hydrodynamic equations. The plasma consists of dynamic relativistic degenerate electrons and positrons and a weakly relativistic ion beam. The Zakharov‐Kuznetsov equation is derived using the standard reductive perturbation technique that admits an obliquely propagating soliton solution. It is found that two types of quantum acoustic modes, that is, a slow acoustic mode and fast acoustic mode, could be propagated in our plasma model. The parameter that determines the nature of soliton, that is, compressive or rarefactive soliton, for slow mode is investigated. Our numerical results show that for the slow mode, the determining parameter is ion beam velocity in the case of relativistic degenerate electrons. We also have examined the effects of plasma parameters (like the beam velocity, the density ratio of positron to electron, the relativistic factor, and the propagation angle) on the characteristics of solitary waves.

The influence of external magnetic field on the plume of vacuum arc thruster

The vacuum arc thruster (VAT) is considered to be a potential micro-thruster because of its simple structure and high specific impulse. The plume downstream from the cathode spot region of a co-axial type thruster with external magnetic field is analyzed by numerical simulation. Plasma velocity, temperature and density are used to represent the influence of the cathode spot region. When the magnetic field is applied, the plume is significantly affected even at the intensity of 0.03 T. Most ions move around the magnetic induction line, forming a concentrated beam. The beam expansion angle and the ion backflow are controlled therefore. The ion beam total velocity increment is about 20% in the plume while the beam direction is determined significantly by the cathode spot position and the external magnetic field. The deflection angle of the magnetic induction line in the near-field region will bring axial velocity loss. The magnetic field intensity affects little on the ion beam velocity increment while the influence of the initial plasma density change caused by the magnetic field cannot be ignored. Ground experiment data show a large increment of ion beam velocity between the conditions with and without the magnetic field (0.03 T and 0 T), but nearly no obvious variation from 0 to 15 cm downstream of the thruster in the former condition.

Interpretation of core ion cyclotron emission driven by sub-Alfvénic beam-injected ions via magnetoacoustic cyclotron instability

Core ion cyclotron emission (ICE) signals have recently been observed in beam-heated plasmas on several tokamaks. In this manuscript we present experimental evidence in support of core ICE being generated by the magnetoacoustic cyclotron instability (MCI), itself driven by the velocity-space inversion of sub-Alfvénic beam-injected ions. The observed core ICE amplitude evolution in beam-heated plasmas is consistent with the MCI and is a result of competition between the beam ion fraction build-up (which increases the instability growth rate) and the slowing down of the dominant beam ion velocity component (which stabilizes the MCI). The oblique propagation angle is constrained to lie in the range 75–78°, where the lower bound is governed by the fast wave reabsorption losses on plasma electrons and bulk ions and the upper bound is governed by the experimentally observed ICE amplitude growth time. Although the oblique MCI is a local theory and does not provide information on the radial mode localization, the calculated instability growth rates are broadly consistent with the observed dynamics of the core ICE amplitude on the ASDEX Upgrade tokamak.

Smoothly Varying Injected Neutral Beam Voltage and Current Provides New Capability on the DIII-D Tokamak

A significant engineering upgrade of the DIII-D neutral beam system has recently completed, providing ability to smoothly and independently vary the beam voltage and current. This enables greater control of the injected beam power, torque, and plasma instability drive for fusion experiments. Modifications to the high-voltage equipment and the plasma control system were made and tested over the last year to allow beam energy to vary by as much as 20 kV over a 0.5-s period anywhere within the 45–85 kV operating range of the beams. The beam current can be made to track the voltage (keeping the perveance constant), or the current and voltage can be varied independently (scanning the perveance). The smooth variation of beam energy avoids the extremely perturbative effects of pulsewidth modulation, the only tool previously used for regulating the injected neutral beam power. With independent control of voltage and current, the beam ion velocity space can be tailored to facilitate new experiments that explore, for example, the detrimental effects of Alfven eigenmodes. These modes are driven by energetic particles and can possibly be avoided in steady-state scenarios by timely variation of the beam energy while maintaining constant input power. A description of the modifications made to the power supply and beam controls will be presented, as well as some initial physics results employing the new variable beam energy system.

Ion beams in multi-species plasmas

Argon and xenon ion velocity distribution functions are measured in Ar-He, Ar-Xe, and Xe-He expanding helicon plasmas to determine if ion beam velocity is enhanced by the presence of lighter ions. Contrary to observations in mixed gas sheath experiments, we find that adding a lighter ion does not increase the ion beam speed. The predominant effect is a reduction of ion beam velocity consistent with increased drag arising from increased gas pressure under all conditions: constant total gas pressure, equal plasma densities of different ions, and very different plasma densities of different ions. These results suggest that the physics responsible for the acceleration of multiple ion species in simple sheaths is not responsible for the ion acceleration observed in expanding helicon plasmas.

Effect of Ion Beam on Dust-Acoustic Waves Under Transverse Perturbations in Dusty Plasma

The dynamics of dust-acoustic waves (DAWs) is studied in the present investigation under transverse perturbations. We have considered dusty plasma consisting of negatively charged dust fluid, non-Maxwellian electrons, and ions embedded with positive ion beam. The Kadomtsev–Petviashvili (KP) equation is derived using a reductive perturbation method. From the solution of KP equation, the characteristics of DAWs have been studied under the influence of various plasma parameters in the presence of beam. It is noticed that characteristics (amplitude, width, and energy) of DAWs are very sensitive to the variation of the values of plasma parameters, such as ion density, beam density, beam velocity, and superthermality of ions and electrons.

Pressure dependence of an ion beam accelerating structure in an expanding helicon plasma

We present measurements of the parallel ion velocity distribution function and electric field in an expanding helicon source plasma plume as a function of downstream gas pressure and radial and axial positions. The ion beam that appears spontaneously in the plume persists for all downstream pressures investigated, with the largest parallel ion beam velocities obtained for the lowest downstream pressures. However, the change in ion beam velocity exceeds what would be expected simply for a change in the collisionality of the system. Electric field measurements confirm that it is the magnitude of the potential structure responsible for accelerating the ion beam that changes with downstream pressure. Interestingly, the ion density radial profile is hollow close to the end of the plasma source for all pressures, but it is hollow at downstream distances far from the source only at the highest downstream neutral pressures.