Resonant Acceleration Research Articles

Acceleration of protons and heavy ions to suprathermal energies during dipolarizations in the near-Earth magnetotail

Abstract. In this work we present an analysis of the dynamics of suprathermal ions of different masses (H+, He+, O+) during prolonged dipolarizations in the near-Earth magnetotail (X>-17RE) according to Cluster/RAPID observations in 2001–2005. All dipolarizations from our database were associated with fast flow braking and consisted of multiple dipolarization fronts (DFs). We found statistically that fluxes of suprathermal ions started to increase ∼1 min before the dipolarization onset and continued to grow for ∼1 min after the onset. The start of flux growth coincided with the beginning of a decrease in the spectral index γ. The decrease in γ was observed for protons for ∼1 min after the dipolarization onset, and for He+ and O+ ions for ∼3 and ∼5 min after the onset respectively. The negative variations of γ for O+ ions were ∼2.5 times larger than for light ions. This demonstrates more efficient acceleration for heavy ions. The strong negative variations of γ were observed in finite energy ranges for all ion components. This indicates the possibility of nonadiabatic resonant acceleration of ions in the course of their interaction with multiple DFs during dipolarizations. Our analysis showed that some fraction of light ions can be accelerated up to energies ≥600 keV and some fraction of oxygen ions can be accelerated up to ∼1.2 MeV. Such strong energy gains cannot be explained by acceleration at a single propagating DF and suggest the possibility of multistage ion acceleration in the course of their interaction with multiple DFs during the prolonged dipolarizations.

Transformer-ratio optimization in nonlinearly driven hollow plasma channels

Acceleration to high energies in electron-driven wakefield accelerators requires a carefully tailored drive beam. High driver currents can, however, modify the accelerating structure response, shifting the optimal driver profile. In this work we present a simple model to describe this nonlinear beamloading in hollow plasma channels. The increase in channel radius and the generation of a return current in the bulk plasma act to modify the resonant frequency and accelerator loss factor. Modeling these effects allows the optimal driver profile to be calculated.

Charged particle nonlinear resonance with localized electrostatic wave-packets

A resonant wave-particle interaction, in particular a nonlinear resonance characterized by particle phase trapping, is an important process determining charged particle energization in many space and laboratory plasma systems. Although an individual charged particle motion in the nonlinear resonance is well described theoretically, the kinetic equation modeling the long-term evolution of the resonant particle ensemble has been developed only recently. This study is devoted to generalization of this equation for systems with localized wave packets propagating with the wave group velocity different from the wave phase velocity. We limit our consideration to the Landau resonance of electrons and waves propagating in an inhomogeneous magnetic field. Electrons resonate with the wave field-aligned electric fields associated with gradients of wave electrostatic potential or variations of the field-aligned component of the wave vector potential. We demonstrate how wave-packet properties determine the efficiency of resonant particle acceleration and derive the nonlocal integral operator acting on the resonant particle distribution. This operator describes particle distribution variations due to interaction with one wave-packet. We solve kinetic equation with this operator for many wave-packets and show that solutions coincide with the results of the numerical integration of test particle trajectories. To demonstrate the range of possible applications of the proposed approach, we consider the electron evolution induced by the Landau resonances with packets of kinetic Alfven waves, electron acoustic waves, and very oblique whistler waves in the near-Earth space plasma.

Experimental Study on a New Reinforcement Method for Multilayer Industrial Building’s Vibration

In order to study a new reinforcement method for multilayer (4 layers) industrial building’s vibration, firstly, a new reinforcement method using a short‐pier shear wall was put forward. Secondly, an engineering example of a multilayer industrial building with abnormal vibration was introduced. A three‐dimensional finite element model of multilayer industrial building was established, and field vibration test was carried out. Test results showed that abnormal vibration of industrial building was caused by resonance between machines and multilayer industrial building. Finally, multilayer industrial building was reinforced by a new reinforcement method, and vibration experiment was carried out after reinforcement. The results show that the new reinforcement method has a good reinforcement effect. Strength and stiffness of multilayer industrial building were obviously improved, and natural frequency of industrial building in the length direction increased from 2.45 Hz to 5.87 Hz, natural frequency of industrial building in the width direction increased from 2.94 Hz to 7.83 Hz, frequencies of machines and frequencies of multilayer industrial building were not in resonance range, acceleration and velocity vibration characteristics of multilayer industrial building were improved, which can provide reference for the reinforcement of multilayer industrial building with a similar structural configuration.

Low-Power Resonant Acceleration Switch for Unattended Sensor Wake-Up

We have designed, built, and tested novel low-power (less than 10 nW) resonant acceleration switches. The switches respond to vibration at specifically designed frequencies between 30 and 1000 Hz by resonating with sufficient displacement to close an electrical contact and consume power only while vibration is occurring. A rotational design avoids switch closings from DC acceleration, and the quality factor, adjustable between 102 and 105 by tuning the vacuum level, sets the resonant detection threshold. The design includes electrostatic combs for self-test and frequency tuning (up to several Hz), compliant contacts to reduce squegging and contact damage, and ruthenium-coated contacts for improved reliability. Fabrication is accomplished with deep reactive ion etching at up to 50:1 aspect ratios, HF vapor release, and XeF2 frequency trimming (up to 30% of the as-fabricated frequency). Testing with vibration recordings played back through a shaker table demonstrates that the switches correctly identify a target without any false alarms. [2018-0061]

Extended Survey of Saturn Z‐Mode Wave Intensity Through Cassini's Final Orbits

AbstractSimilar to whistler mode chorus, Z‐mode emission is an efficient diffusive scatterer of electrons possibly resulting in resonant acceleration. We present results of a survey of both the low‐band (5 kHz) and for the first time the high‐band (20 kHz) intensity of these emissions, based on over 11 years of Cassini Radio and Plasma Wave Science instrument data including nine ring‐grazing orbits and two proximal orbits, which occurred at the end of the mission. We distinguish these emissions using density and polarization measurements and calculate the mean intensity as a function of frequency and spatial coordinates. We find that the average low‐band Z‐mode intensity peak is P0 ~7 × 10−8 nT2, while the high‐band peak is much lower at P0 ~10−9 nT2. The spatial distribution of intensity differs for each emission band implying different source regions and perhaps different source mechanisms.

Analysis of Intense Z‐Mode Emission Observed During the Cassini Proximal Orbits

AbstractThe role of Z‐mode emission in the diffusive scattering and resonant acceleration of electrons is believed to be important at Saturn. A survey of the “5 kHz” component of this emission at Saturn earlier reported strong intensity in the lower density regions where the ratio of plasma frequency to cyclotron frequency, fp/fc < 1. At Saturn this occurs along the inner edge of the Enceladus torus near the equator and at higher latitudes. Using the Cassini Radio and Plasma Wave Science instrument observations during the Cassini proximal orbits, we have now identified these emissions extending down to and within the ionosphere. Wave polarization measurements and unique frequency cutoffs are used to positively identify the wave mode. Analogous to the role of whistler mode chorus at Earth, Saturn Z‐mode emissions may interact with electrons contributing to the filling or depleting of Saturn's inner radiation belts.

Analysis of Harmonic Vibration Characteristics for a Composite Honeycomb Panel of the Spacecraft Scanner

The coordinate and frequency distributions of the values of displacement and acceleration amplitudes, the vibration acceleration amplification factors, and the equivalent von Mises stresses are obtained from the data on the simulation modeling of harmonic vibration of the composite honeycomb panel for spacecraft scanner and its related operational equipment (a scanner, magnetometer, optical devices, etc.) mounted on it. A dynamic simulation model of the composite honeycomb panel was developed using modern finite element analysis tools, such as ANSYS APDL. Carbon fiber reinforced plastic plates with an aluminum foil honeycomb core in the form of regularly shaped hexagonal cells that make up the honeycomb panel are approximated by multilayer plate finite elements. The related operational equipment, such as optical devices, a scanner and magnetometer, are represented in the model by lumped masses rigidly attached to the panel. The spectrum of natural frequencies and vibration modes of the spacecraft scanner honeycomb panel is determined using the developed simulation model. The resonant displacement and acceleration amplitudes, the vibration acceleration amplification factors as well as the distributions of the amplitudes of the equivalent von Mises stresses are obtained in the operating frequency range of the investigated harmonic vibration mode of the spacecraft scanner honeycomb panel.

Betatron resonance electron acceleration and generation of relativistic electron beams using 200 fs Ti:sapphire laser pulses

The generation of relativistic electron beams with quasi-thermal energy distribution (maximum energy: 30 MeV) by the interaction of a Ti:sapphire laser pulse of 200 fs duration, focussed to an intensity of ∼2.1 × 1018 W cm−2, with an underdense (electron density ∼3.6 × 1019 to ∼1.1 × 1020 cm−3) He gas-jet plasma was observed. We observed two stages of self-focusing of the laser pulse in the plasma. Two groups of accelerated electrons associated with these two stages of laser channeling were also observed, and are attributed to the betatron resonance acceleration mechanism. This is supported by 2D PIC simulations performed using the EPOCH code and a detailed theoretical analysis. Further, the generation of quasi-monoenergetic (ΔE/E ∼ 10%–20%) electron beams with a peak energy of ∼17–22 MeV was also observed, even with such long laser pulses, although with a low probability of occurrence.

Contrasting dynamics of electrons and protons in the near-Earth plasma sheet during dipolarization

Abstract. The fortunate location of Cluster and the THEMIS P3 probe in the near-Earth plasma sheet (PS) (at X ∼ −7–−9 RE) allowed for the multipoint analysis of properties and spectra of electron and proton injections. The injections were observed during dipolarization and substorm current wedge formation associated with braking of multiple bursty bulk flows (BBFs). In the course of dipolarization, a gradual growth of the BZ magnetic field lasted ∼ 13 min and it was comprised of several BZ pulses or dipolarization fronts (DFs) with duration ≤ 1 min. Multipoint observations have shown that the beginning of the increase in suprathermal (> 50 keV) electron fluxes – the injection boundary – was observed in the PS simultaneously with the dipolarization onset and it propagated dawnward along with the onset-related DF. The subsequent dynamics of the energetic electron flux was similar to the dynamics of the magnetic field during the dipolarization. Namely, a gradual linear growth of the electron flux occurred simultaneously with the gradual growth of the BZ field, and it was comprised of multiple short (∼ few minutes) electron injections associated with the BZ pulses. This behavior can be explained by the combined action of local betatron acceleration at the BZ pulses and subsequent gradient drifts of electrons in the flux pile up region through the numerous braking and diverting DFs. The nonadiabatic features occasionally observed in the electron spectra during the injections can be due to the electron interactions with high-frequency electromagnetic or electrostatic fluctuations transiently observed in the course of dipolarization. On the contrary, proton injections were detected only in the vicinity of the strongest BZ pulses. The front thickness of these pulses was less than a gyroradius of thermal protons that ensured the nonadiabatic acceleration of protons. Indeed, during the injections in the energy spectra of protons the pronounced bulge was clearly observed in a finite energy range ∼ 70–90 keV. This feature can be explained by the nonadiabatic resonant acceleration of protons by the bursts of the dawn–dusk electric field associated with the BZ pulses. Keywords. Magnetospheric physics (Magnetotail; plasma sheet) – Space plasma physics (Transport processes)

Long-term evolution of electron distribution function due to nonlinear resonant interaction with whistler mode waves

Accurately modelling and forecasting of the dynamics of the Earth’s radiation belts with the available computer resources represents an important challenge that still requires significant advances in the theoretical plasma physics field of wave–particle resonant interaction. Energetic electron acceleration or scattering into the Earth’s atmosphere are essentially controlled by their resonances with electromagnetic whistler mode waves. The quasi-linear diffusion equation describes well this resonant interaction for low intensity waves. During the last decade, however, spacecraft observations in the radiation belts have revealed a large number of whistler mode waves with sufficiently high intensity to interact with electrons in the nonlinear regime. A kinetic equation including such nonlinear wave–particle interactions and describing the long-term evolution of the electron distribution is the focus of the present paper. Using the Hamiltonian theory of resonant phenomena, we describe individual electron resonance with an intense coherent whistler mode wave. The derived characteristics of such a resonance are incorporated into a generalized kinetic equation which includes non-local transport in energy space. This transport is produced by resonant electron trapping and nonlinear acceleration. We describe the methods allowing the construction of nonlinear resonant terms in the kinetic equation and discuss possible applications of this equation.

Modelling of pulse train generation for resonant laser wakefield acceleration using a delay mask

A new method for the generation of a train of pulses from a single high-energy, ultra short pulse is presented, suited for Resonant Multi-Pulse Ionization injection (Tomassini, 2017). The method is based on different transverse portion of the pulse being delayed by a “mask” sectioned in concentric zones with different thicknesses, in order to deliver multiple laser pulses. The mask is placed right before the last focusing parabola. A hole in the middle of the mask lets part of the original pulse to pass through to drive electron injection. In this paper a full numerical modelling of this scheme is presented. In particular we discuss the spatial and temporal profile of the pulses emerging from the mask and how they are related to the radius and thickness of each section.

Дилатометрический микродвигатель малого космического аппарата с резонансным СВЧ-ускорителем

Дилатометрический микродвигатель малого космического аппарата с резонансным СВЧ-ускорителем

Gamma-ray generation from laser-driven electron resonant acceleration: In the non-QED and the QED regimes

Electron acceleration and γ-ray emission by circularly polarized laser pulses interacting with near-critical-density plasmas are systematically investigated for both the non-quantum-electrodynamic (non-QED) and QED regimes. In the non-QED regime, since electron density in the plasma channel is small and the self-generated electromagnetic fields are weak, only a few electrons can achieve the resonant acceleration, leading to weak γ-ray emission. However, when it comes to the QED regime, the radiation recoil force significantly affects the electron dynamics, which helps in not only the trapping of electrons, but also the relaxing of the condition for electrons to hit the resonance with laser fields, resulting in the formation of an ultradense helical electron bunch under resonant acceleration in the plasma channel. Therefore, an intense γ-ray pulse with unprecedented flux can be generated. Theoretical analysis and three-dimensional particle-in-cell simulations are carried out to compare the dynamics in two different regimes.

Combined influence of azimuthal and axial magnetic fields on resonant electron acceleration in plasma

Resonant enhancement in electron acceleration due to a circularly polarized laser pulse in plasma, under the combined influence of external azimuthal and axial magnetic fields, is studied. We have investigated direct electron acceleration in plasma by employing a relativistic single particle simulation. The plasma is magnetized with an azimuthal magnetic field applied in the perpendicular plane and an axial magnetic field applied along the direction of laser beam propagation. Resonance takes place between electron and electric field of the laser pulse for the optimum value of the combined magnetic field, which supports electron acceleration to higher energies, up to the betatron resonance point. The optimum value of these magnetic fields is highly sensitive to laser initial intensity and laser initial spot size. The effects of laser intensity, initial spot size, and laser pulse duration are taken into consideration in optimizing the magnetic field for efficient electron acceleration. Higher electron energy gain, of the order of GeV, is observed by employing terawatt circularly polarized laser pulses in plasma under the influence of combined magnetic field of about 10 MG.

Breakdown of the ponderomotive approximation as an acceleration mechanism in wave-particle nonlinear dynamics

In the present analysis, we study the dynamics of charged particles submitted to the action of slowly modulated electromagnetic carrier waves. While the velocity of the particles remains smaller than the carrier's phase-velocity, their dynamics is well described by a refined ponderomotive approach. The ponderomotive approach has its own validity limits well established, beyond which particles are resonantly trapped by the carrier waves. We show that under adequate conditions, the trapping mechanism places particles at an optimal relative phase with respect to the carrier for maximum acceleration. In addition to the analytical approach involved in the ponderomotive description, we use numerical simulations to validate the corresponding dynamics as well as to explore various features of the resonant trapping and acceleration.

GV/cm scale laser-magnetic resonant acceleration in vacuum

AbstractResonant acceleration of electrons by a laser in the background of an extra longitudinal magnetic field is investigated analytically and numerically. The resonant condition is independent of laser intensity, and when satisfied, the energy gain is proportional to $a_0^2 $ and the square of phase difference. This process is mainly limited by the magnitude and spatial size of the extra magnetic field. Under the laboratory conditions, simulation results show that a monoenergetic and collimated electron bunch can still be obtained in ~ GV/cm scale, which sheds a light on the vacuum table-top laser-driven electron accelerators.

On the self-oscillation in a pulsed RF amplifying–accelerating system

A number of resonant accelerators of charged particles are fed by high power RF amplifiers loaded by resonant accelerating structures. Some of the accelerators such as linacs and racetrack microtrons are employed in self-oscillating mode using a positive feedback loop. That scheme allows a self-adjusted operation tolerable to significant changes in temperature and beam loading. However, in general such a system may develop instabilities. In this paper we consider a simplified model of an amplifier (e.g., a klystron) self-starting generation from noise and loaded by a resonant structure. Some typical transients including reflected power and influence of group delays are evaluated numerically.

Production of high-angular-momentum electron beams in laser-plasma interactions.

It was shown that in the interactions of ultra-intense circularly polarized laser pulse with the near-critical plasmas, the angular momentum can be transferred efficiently from the laser beam to electrons through the resonance acceleration process. The transferred angular momentum increases almost linearly with the acceleration time t_{a} when the electrons are resonantly accelerated by the laser field. In addition, it is shown analytically that the averaged angular momentum of electrons is proportional to the laser amplitude a_{L}, and the total angular momentum of the accelerated electron beam is proportional to the square of the laser amplitude a_{L}^{2} for a fixed parameter of n_{e}/n_{c}a_{L}. These results are verified by three-dimensional particle-in-cell simulations. This regime provides an efficient and compact alternative for the production of high angular momentum electron beams, which may have many potential applications in condensed-matter spectroscopy, new electron microscopes, and bright x-ray vortex generation.

Brilliant petawatt gamma-ray pulse generation in quantum electrodynamic laser-plasma interaction

We show a new resonance acceleration scheme for generating ultradense relativistic electron bunches in helical motions and hence emitting brilliant vortical γ-ray pulses in the quantum electrodynamic (QED) regime of circularly-polarized (CP) laser-plasma interactions. Here the combined effects of the radiation reaction recoil force and the self-generated magnetic fields result in not only trapping of a great amount of electrons in laser-produced plasma channel, but also significant broadening of the resonance bandwidth between laser frequency and that of electron betatron oscillation in the channel, which eventually leads to formation of the ultradense electron bunch under resonant helical motion in CP laser fields. Three-dimensional PIC simulations show that a brilliant γ-ray pulse with unprecedented power of 6.7 PW and peak brightness of 1025 photons/s/mm2 /mrad2 /0.1% BW (at 15 MeV) is emitted at laser intensity of 1.9 × 1023 W/cm2.