Deceleration Of Beam Research Articles

Effect of magnetic field on deceleration of ion beam in plasma with ion-acoustic turbulence

The deceleration of a monoenergetic rarefied ion beam in nonisothermal plasma in a constant magnetic field has been studied. It is shown how ion-acoustic turbulence generated by a current along the magnetic field leads to an effective decrease in the velocity of ions moving with a speed higher than the speed of ion sound. When an ion beam is injected into plasma across the magnetic field, the trajectory of the ions has the form of a contracting spiral elongated along the magnetic field. The deceleration occurs due to the Cherenkov interaction of ions with ion-acoustic waves and stops when the ion velocity decreases to the speed of ion sound. The braking lengths and the beam velocity components, which are set at the moment of stopping braking, are found. After the end of deceleration, the ions move with constant velocity in a spiral along the magnetic field.

Feasibility of a strong focusing synchrotron for cold neutron beams

We study the feasibility of storing cold neutron beams in a strong focusing synchrotron. We also propose an alternating-current (ac) dipole magnet to be used as a neutron acceleration device and a pulsed quadrupole as a neutron beam kicker for injection and extraction. The ac acceleration device can provide adiabatic capture, acceleration, or deceleration of neutron beams. It seems feasible to design a high-quality neutron synchrotron for many future neutron beam applications, such as neutron life time measurements, monoenergetic neutron scattering experiments, and pencil neutron beam applications. This synchrotron can also be used as an injector for a neutron accumulator ring. Published by the American Physical Society 2024

Deceleration of fast ion rarefied beam due to Cherenkov interaction with ion-acoustic waves.

The deceleration of a low-density beam of ions in plasma with developed ion-acoustic turbulence arising in strong electric field is described. The time and length of beam deceleration along and across the anisotropy axis of the wave number distribution of ion-acoustic waves are found. It is shown to what extent an increase in the strength of the electric field that generates turbulence is accompanied by a decrease in the time and length of braking. As the beam propagates along the anisotropy axis, its velocity decreases to approximately the velocity of ion sound, and the direction of propagation does not change. When the beam is decelerated with an initial velocity across the anisotropy axis, a velocity component appears along the anisotropy axis during deceleration, which results in the beam deflection from the initial direction. In this case, the modulus of the beam velocity at the end of deceleration is close to the ion sound velocity.

Storage, accumulation and deceleration of secondary beams for nuclear astrophysics

Low-energy investigations on rare ion beams are often limited by the available intensity and purity of the ion species in focus. Here, we present the first application of a technique that combines in-flight production at relativistic energies with subsequent secondary beam storage, accumulation and finally deceleration to the energy of interest. Using the FRS and ESR facilities at GSI, this scheme was pioneered to provide a secondary beam of 118Te52+ for the measurement of nuclear proton-capture at energies of 6 and 7 MeV/u. The technique provided stored beam intensities of about 106 ions at high purity and brilliance, representing a major step towards low-energy nuclear physics studies using rare ion beams.

Electron Temperature Anisotropy Effects on Alpha/Proton Instability in the Solar Wind

In situ recordings by the solar Wind spacecraft reveal the ubiquitousness of alpha particles, whose drift velocities to the background proton vα are generally less than or equal to the local Alfvén velocity vA. The alpha beam instability plays a significant role in the alpha beam deceleration in the solar wind; nonetheless, the detailed mechanism of deceleration remains unclear. By using the linear Vlasov equation of the PDRK/B0 solver, the present work investigates the kinetic instability caused by both the alpha beam and the electron temperature anisotropy in the solar wind and assesses the effects of the electron temperature anisotropy on such instability. The results show that both anisotropic electrons and alpha beams lead to the excitation of several plasma waves, and the wave frequency, growth rate, and polarization properties are sensitive to the electron temperature anisotropy (Te⊥/Te‖), the parallel electron beta (βe‖), and the alpha beam drift velocity (vα/vA). With an excess parallel temperature Te⊥/Te‖<1, the parallel magnetosonic/whistler (PM/W), parallel Alfvén wave (PAW), and oblique Alfvén/ion cyclotron (OA/IC) instabilities could be generated, while for an excess perpendicular temperature Te⊥/Te‖>1, the PM/W, OA/IC, parallel whistler (PW), and kinetic Alfvén wave (KAW) instabilities could grow. In the region of Te⊥/Te‖<1, the thresholds of the PM/W, PAW, and OA/IC instabilities extend to lower drift velocity vα/vA. In the region of Te⊥/Te‖>1, the thresholds of the PM/W and OA/IC instabilities increase, while those of the PW and KAW instabilities are shifted to lower vα/vA. The current study presents a comprehensive overview for alpha beam instabilities that limit the alpha beam drift velocity in the solar wind.

An advanced radio-frequency quadrupole ion cooler for accelerator mass spectrometry

An advanced radio-frequency quadrupole (RFQ) ion cooler was developed for accelerator mass spectrometry to use element-selective laser photodetachment and ion-molecule reactions for isobar suppression. The system will be installed as a central part of the new Anion Laser Isobar Separator (ALIS) at the 6 MV AMS system of CologneAMS.The new RFQ design intends to solve the technical challenge of the deceleration and trapping of heavy molecular ion beams with high emittance. Therefore, an elliptical injection electrode was developed to slow down the ions far away from the central entrance aperture. A new and easy-to-manufacture guide-field assembly was developed. For this purpose, diagonally-split cylindrical surface electrodes are capacitively coupled to a core rod that is carrying the RF signal. Consequently, only low DC voltages are needed to create a gradually changing potential in the longitudinal direction. The RFQ and the acceleration electrodes are installed in a self-aligned structure.

Dual projectile beams.

Accelerating beams, of which the Airy beam is an important representative, are characterized by intensity maxima that propagate along curved trajectories. In this work we present a simple approach to directly generate accelerating beams with controllable trajectories by means of binary phase structures that consist of only a π phase step modulation in comparison to previous studies where two-dimensional cubic phase modulations for example are required, and which have practical limitations due to their challenging fabrication with phase plates or diffractive optical elements (DOEs), or the spatially extended system needed for their generation at the Fourier plane. In our approach, two intensity maxima are formed that propagate along root parabolic trajectories in contrast to Airy and higher order caustic beams that propagate along a parabolic curve, hence we call these beams Dual Projectile Beams (DPBs). By tailoring a step or slit phase patterns with additional Fresnel lenses, we either generate hollow-core or abruptly focusing beams and control their curvatures. Moreover, using DPBs as a simpler complement to complex structured light fields, we demonstrate their versatility at the example of their interaction with nonlinear matter, namely the formation of a spatial soliton in a photorefractive material. We show that the formed solitary state propagates almost unchanged for a distance of several Rayleigh lengths. This light matter interaction can be regarded as a light beam deceleration. The simplicity of this approach makes these beams suitable for integrated optics and high-power laser applications using DOEs or meta-surfaces.

Optimized deceleration characteristics of multicharged ion beams from electron cyclotron resonance ion source

At present it is necessary the satellite lifetime 10-15 years for operating in space. Xenon is used as fuel for ion engines of satellites. There are problems of accumulated damages at irradiation and sputtering by low energy Xe ion from the engine. It is required to construct database of sputtering yield of ion beams in the low energy region from a hundred eV to 1keV. We are trying to investigate experimentally sputtering yield on satellite component by irradiating the low energy Xe q+ ion beams. We use the electron cyclotron resonance ion source (ECRIS) in the irradiation experiments. We decelerate the beam energy to several hundred eV after extraction at high voltage 10kV. It is found we cannot neglect the contribution of the space potential of the plasma in the ECRIS of several tens eV. We measured the plasma parameters and ion beam deceleration characteristics in operating conditions on ECRIS. As the results, it was found in operating ECRIS condition of low charge state ion being dominant that the space potential of the ECRIS has an effect of 10∼20% at the beam energy at about 100eV in conducting irradiation experiments on satellite component materials.

Correlative volume-imaging using combined array tomography and FIB-SEM tomography with beam deceleration for 3D architecture visualization in tissue.

Focused ion beamed (FIB) SEM has a higher spatial resolution than other volume-imaging methods owing to the use of ion beams. However, in this method, it is challenging to analyse entire biological structures buried deep in the resin block. We developed a novel volume-imaging method by combining array tomography and FIB-SEM tomography and investigated the chondrocyte ultrastructure. Our method imparts certainty in determining the analysis area such that cracks or areas with poor staining within the block are avoided. The chondrocyte surface showed fine dendritic processes that were thinner than ultrathin sections. Upon combination with immunostaining, this method holds promise for analysing mesoscopic architectures.

Alpha/proton Instability in the Presence of Proton and Alpha Temperature Anisotropy and its Application to the Deceleration of Alpha Particles in the Solar Wind

Observations of solar wind plasma find that the drift velocity between alpha beams and protons, v α , is reduced with the heliocentric distance, but the ratio of v α to v A (the local Alfvén velocity) does not vary obviously and has a typical velocity ratio of v α /v A ≤ 1. The alpha beam instability is believed to be responsible for the deceleration of alpha beams in the solar wind. However, the role of the temperature anisotropy of ions (protons and alpha particles) on the alpha beam instability has not been examined. Based on the kinetic theory of the PDRK solver, this study systemically investigates the alpha beam instability in the presence of proton and alpha temperature anisotropies and considers the effects of these temperature anisotropies on the instability at an arbitrary propagation angle relative to the ambient magnetic field. It is found that the real frequencies, growth rates and threshold conditions of the excited waves sensitively depend on the proton temperature anisotropy T i⊥/T i∥ and the alpha temperature anisotropy T α⊥/T α∥, as well as the parallel electron beta β e∥. In particular, for both alpha beam and proton temperature anisotropy driven cases, the parallel magnetosonic/ whistler (PM/W), backward magnetosonic/ whistler (BM/W) and oblique Alfvén/ion cyclotron (OA/IC) waves arise when T i⊥/T i∥ < 1, and the PM/W, OA/IC, parallel Alfvén/ion cyclotron (PA/IC) and mirror waves occur when T i⊥/T i∥ > 1. The presence of anisotropic protons leads to a lower velocity threshold for the OA/IC and BM/W waves at T i⊥/T i∥ < 1 and for the OA/IC, PA/IC and mirror waves at T i⊥/T i∥ > 1. For both alpha beam and alpha temperature anisotropy driven cases, the PM/W and OA/IC waves are unstable when T α⊥/T α∥ < 1, and the PM/W, OA/IC, PA/IC, oblique magnetosonic/ whistler (OM/W) and mirror waves are likely to grow as T α⊥/T α∥ > 1. The presence of anisotropic alpha particles results in a lower threshold velocity for the PM/W wave at T α⊥/T α∥ < 1 and for the PA/IC, OM/W and mirror waves at T α⊥/T α∥ > 1. On account of the influences of the anisotropic proton and alpha, these alpha beam instabilities can effectively constrain the alpha-beam drift velocity to less than or equal to the local Alfvén velocity. These results may shed light on the evolution and deceleration mechanism of alpha particles in the solar wind.

Quantification of STEM Images in High Resolution SEM for Segmented and Pixelated Detectors.

The segmented semiconductor detectors for transmitted electrons in ultrahigh resolution scanning electron microscopes allow observing samples in various imaging modes. Typically, two standard modes of objective lens, with and without a magnetic field, differ by their resolution. If the beam deceleration mode is selected, then an electrostatic field around the sample is added. The trajectories of transmitted electrons are influenced by the fields below the sample. The goal of this paper is a quantification of measured images and theoretical study of the capability of the detector to collect signal electrons by its individual segments. Comparison of measured and ray-traced simulated data were difficult in the past. This motivated us to present a new method that enables better comparison of the two datasets at the cost of additional measurements, so-called calibration curves. Furthermore, we also analyze the measurements acquired using 2D pixel array detector (PAD) that provide a more detailed angular profile. We demonstrate that the radial profiles of STEM and/or 2D-PAD data are sensitive to material composition. Moreover, scattering processes are affected by thickness of the sample as well. Hence, comparing the two experimental and simulation data can help to estimate composition or the thickness of the sample.

Improvement of type-I method for observing magnetic contrast using scanning electron microscope under tilting-deceleration condition

We developed a method of observing SEM images with a clear magnetic contrast without anisotropy using a scanning electron microscope (SEM). Directional-selective detection of secondary electrons (SEs) is needed to obtain SEM images with a clear magnetic contrast using a type-I method that utilizes changes in the number of detected signals due to a deflection of SEs by the stray magnetic fields of specimens. By combining beam deceleration and specimen tilting (hereinafter “tilting deceleration”), we achieved a directional-selective detection condition for SEs that is preferable for the type-I method. We found that the tilting deceleration method has high sensitivity for fine magnetic domain structures and can visualize submicron-sized magnetic domain structures in a vertically magnetized region of Nd2Fe14B specimens. Furthermore, we synthesized two SEM images with different directional information to reduce the anisotropy of magnetic contrast obtained by the asymmetric detector configuration. As a result, we obtained SEM images with isotropic magnetic contrast, which is similar to that of an SEM image acquired by a spin-SEM equipped with a Mott-type spin-polarization detector.

Detection of oscillatory solutions in a vacuum diode with total electron reflection

Stability features of steady-state solutions for a vacuum diode with complete deceleration of electron beam is studied. A boundary line on the (inter-electrode gap, external voltage)-plane separating stable solutions from unstable ones is built up. An instability development is shown to end in a state with non-linear oscillations of the electric field but with no virtual cathode in a plasma. Existence of non-linear oscillations of the electric field in a vacuum diode with total reflection of an electron beam points out that such a diode can be a basis to create microwave generator.

Properties of the 90° cylindrical energy analyzer with internal deceleration of the beam in real conditions of operation

To measure plasma potential in toroidal magnetically confined fusion plasma, the Heavy Ion Beam Diagnostic (HIBD) employs of the electrostatic energy analyzer. The 90° cylindrical energy analyzer (CEA) developed for the HIBD on the ISTTOK tokamak due to compactness and multislit operation capability, is characterized by large angular aberrations, if operated in conventional mode. A new operation regime was proposed based on numerical investigations, which demonstrated the efficiency of the 90°CEA operation in reducing angular aberrations via the deceleration of the ion beam inside analyzer, resulting also on an improved energy resolution. In this paper, the properties of the 90 ° CEA featuring with guard rings (GR) to shield the analyzer from the surrounding structures are investigated in the internal deceleration mode (ID-mode) for “centric” and “paracentric” injection geometries. The numerical simulations are conducted using SIMION code. Special attention is paid to uniformity of the beam image on detector plate, which is of importance in ion beam energy measurements by split-plate detector technique. The results confirm coupling of analyzer angle aberration properties with beam deceleration inside analyzer. For both “centric” and “paracentric” entrances the existence of the first-order focus in ID-mode is obtained. However, the first order focus ID-mode of 90°CEA with GR is characterized by heterogeneity of the image for the initially uniform beam, determined by modification of electric field inside analyzer. It is revealed that the energy dispersion of the initially monoenergetic ions due to chromatic-like aberration introduced by analyzer plays a contributive role in the beam image non-uniformity. From the beam energy measurements point of view, it is shown that the energy variation due to this chromatic aberration is of the second order of the analyzer intrinsic resolution. The results show that “centric” entrance in ID-mode is preferable as the image non-uniformity is less pronounced and can be effectively restored by manipulation of entrance slit dimensions and potentials on GR. It is concluded that besides detail preparatory numerical optimization, the beam image shape and uniformity control is essential, which can be realized with the dedicated multiple cell detection.

Sequential SEM imaging of microbial calcite precipitation consolidation treatment

Cultural heritage built from limestone is prone to deterioration by chemical weathering, a natural process, that is enhanced by pollution. There are many historic monuments built from calcareous rocks that suffer from deterioration, and thus there have been a number of approaches over the last few decades to consolidate these types of rocks and surfaces. Using natural biological processes by fostering the activity of calcite-producing bacteria, also referred to as biomineralization, is one strategy that has also been commercialized. The base of proving the effectiveness of any surface treatment is the observation of the surface at sequential stages before and after treatment, as well as after exposure to weathering. Due to the heterogeneity of natural materials and processes, our aim was to observe identical test areas at the micron scale throughout the observation period. In order to achieve this on a tungsten SEM, we employed a beam deceleration accessory that allowed low kV imaging on non-conductive surfaces at a sufficiently high image resolution with a modified sample holder accommodating drill cores of 25 mm diameter and up to 15 mm height. The presented method is capable of producing time-sequenced images on the same test area on natural rock surface samples without manipulation for imaging purposes. This offers interesting perspectives for effective documentation of such processes in various fields.

Electron bunch evolution in laser-wakefield acceleration

We report on systematic and high-precision measurements of the evolution of electron beams in a laser-wakefield accelerator (LWFA). Utilizing shock-front injection, a technique providing stable, tunable and high-quality electron bunches, acceleration and deceleration of few-MeV quasimonoenergetic beams were measured with cutting-edge technology sub-5-fs and 8-fs laser pulses. We explain the observations with dephasing, an effect that fundamentally limits the performance of LWFAs. Typical density dependent electron energy evolution with $57--300\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ dephasing length and 6--20 MeV peak energy was observed and is well described by a parabolic fit. This is a promising electron source for time-resolved few-fs electron diffraction.

Plasma potential and fluctuations measurements by HIBD with 90° cylindrical energy analyzer on the ISTTOK tokamak

The Heavy Ion Beam Diagnostic (HIBD) is known as unique tool for direct measurements of plasma potential in fusion devices such as tokamaks and stellarators. On small ISTTOK tokamak (R = 0.45 m, a = 0.085 m, B = 0.5 T, Ip = 4 kA, <ne> = 4 × 1018 m−3) the HIBD is operated with primary Xe+ ion beam with E = 22−24 keV of energy and a Multiple Cell Array Detector (MCAD) to measure the product of plasma neσ and its fluctuations simultaneously at a number of sample volumes along primary beam trajectory across the plasma. To upgrade the ISTTOK HIBD capabilities to measure the plasma potential and its fluctuations a multichannel 90° cylindrical electrostatic energy analyzer (CEA) operated in a beam deceleration mode has been proposed.This paper presents the first results of the plasma potential and its fluctuations measurements by the one-channel CEA prototype operated in two-times deceleration mode and in real conditions of the HIBD experiments on ISTTOK. Using an indirect CEA calibration approaches, the value of the potential Φ ∼ −350 V has been measured in the plasma core. Also, the plasma potential fluctuations Φ∼ ∼ 40 V have been observed. The obtained results demonstrate and confirm the applicability of the 90° cylindrical electrostatic energy analyzer and its operation in deceleration mode for the plasma potential and its fluctuations measurements by HIBD.

Improving transport and optimizing deceleration of ion beams from electron cyclotron resonance multicharged ion sources.

Electron cyclotron resonance ion sources (ECRISs) are widely applied for ion beam applications, e.g., plasma processing, cancer therapy, and ion engine of an artificial satellite. In our ECRIS, we aim at producing and extracting various ion beams from this device, in particular, Xeq+ ion beams at low energy. In the aerospace engineering field, there are problems of accumulated damages on various component materials caused by low energy of Xe ions from the engine. There are not enough experimental sputtering data for satellite materials at the Xeq+ in the low energy region. Then, we are trying to investigate the sputtering yield experimentally by irradiating the low energy Xe ion beams. To perform this experiment, it is necessary to acquire a certain amount of beam current with low energy. Then, we generate the low energy ion beams by the following steps: First, the ion beams are extracted from the ECRIS at high voltage. Next, these are transported to an ion beam irradiation system (IBIS). Finally, the ion beams are decelerated by the deceleration voltage in the IBIS. We adjusted the beamline. We measure the characteristics of the transport efficiency and decelerated ion beam currents. In this paper, we describe the experimental setup using an existing ECRIS for decelerated heavy ion beams and the results of decelerated ion beam currents.

Experience of forming combined low-energy electron-ion beams in plasma sources of charged particles

The paper shows the possibility of forming combined electron-ion beams in a single multi-discharge structure that does not contain incandescent elements. A design of the electrode structure of an electron-ion source is proposed, which consists of two «Penning type» discharge cells connected in series (along the axis). It is shown that the interconnection of separately controlled discharges in the structure increases the degree of gas ionization at reduced pressure, as well as the formation of double electric layers in the plasma, which ensure the formation of combined ion-electron flows in a single structure. This is ensured by creating conditions for the drift of the electron beam through the entire part of the electrode structure, which ensures the formation of the ion current of the source, and helps to increase the degree of ionization of the gas in this region. In addition, the deceleration of the electron beam in the ion acceleration gap ensures the return of electrons, which have lost part of their energy to gas ionization, into the region of the formation of the plasma emitting ions. This contributes to an increase in the density of the ion emission current. Some experimental parameters of the beams formed by the developed structure are presented.

Single Shot Characterization of High Transformer Ratio Wakefields in Nonlinear Plasma Acceleration.

Plasma wakefields can enable very high accelerating gradients for frontier high energy particle accelerators, in excess of 10 GeV/m. To overcome limits on single stage acceleration, specially shaped drive beams can be used in both linear and nonlinear plasma wakefield accelerators (PWFA), to increase the transformer ratio, implying that the drive beam deceleration is minimized relative to acceleration obtained in the wake. In this Letter, we report the results of a nonlinear PWFA, high transformer ratio experiment using high-charge, longitudinally asymmetric drive beams in a plasma cell. An emittance exchange process is used to generate variable drive current profiles, in conjunction with a long (multiple plasma wavelength) witness beam. The witness beam is energy modulated by the wakefield, yielding a response that contains detailed spectral information in a single-shot measurement. Using these methods, we generate a variety of beam profiles and characterize the wakefields, directly observing transformer ratios up to R=7.8. Furthermore, a spectrally based reconstruction technique, validated by 3D particle-in-cell simulations, is introduced to obtain the drive beam current profile from the decelerating wake data.