Collective Ion Acceleration Research Articles

Comparison of collective acceleration of ions in a luce diode in residual atmospheres of air, argon and krypton

The paper compares the collective acceleration of ions in a Luce diode in residual atmospheres of air, argon and krypton at pressures of 6–156 mPa, evaluating the efficiency of capture of Ar and Kr ions into collective acceleration from their residual atmospheres. At a diode voltage of ∼232 kV, proton energies were 510 ± 38, 619 ± 62 and 567 ± 59 keV for air, argon, and krypton atmospheres, respectively, while the number of protons per shot was approximately 2 and 3 times higher in the argon and krypton residual atmosphere compared to the normal residual atmosphere. This increase in energy also led to a significant increase in the proportion of protons with energies greater than 3.02 MeV - to 1010 per shot on average. It was found that with increasing argon pressure, the diode current noticeably decreases, and with increasing krypton pressure, on the contrary, the diode current noticeably increases, which can be explained by the fact that argon is more neutral than krypton. The efficiency of capture of Ar and Kr ions into collective acceleration from their residual atmospheres was estimated as 0.06 % and 0.19 %, respectively.

Acceleration of Electrons and Ions by an “Almost” Astrophysical Shock in the Heliosphere

Collisionless shock waves, ubiquitous in the Universe, are crucial for particle acceleration in various astrophysical systems. Currently, the heliosphere is the only natural environment available for their in situ study. In this work, we showcase the collective acceleration of electrons and ions by one of the fastest in situ shocks ever recorded, observed by the pioneering Parker Solar Probe at only 34.5 million km from the Sun. Our analysis of this unprecedented, near-parallel shock shows electron acceleration up to 6 MeV amidst intense multiscale electromagnetic wave emissions. We also present evidence of a variable shock structure capable of injecting and accelerating ions from the solar wind to high energies through a self-consistent process. The exceptional capability of the probe’s instruments to measure electromagnetic fields in a shock traveling at 1% the speed of light has enabled us, for the first time, to confirm that the structure of a strong heliospheric shock aligns with theoretical models of strong shocks observed in astrophysical environments. This alignment offers viable avenues for understanding astrophysical shock processes and the self-consistent acceleration of charged particles.

Revisiting the Luce diode in the context of recent research on multi-vircators with dielectric reflectors

Recently, in a series of articles Mumtaz, Choi, and others [i.e., S. Mumtaz and E. Choi, IEEE Electronic Device Lett. 43, 1756 (2022)] studied a relativistic gridded vircator with one or more dielectric anodes, in which considerable increase in the efficiency of high-power microwave (HPM) generation compared to ordinary vircators was observed. This is very important since the main disadvantage of vircators is their low efficiency. It was suggested that the repelling of electrons by the initial impacting electron charge collected on the dielectric reflectors forms a multi-vircator, which increases HPM production. The present article reports the results of experiments and numerical simulations, which show that this mechanism does not result in high multi-vircator efficiency. Similar dielectric anodes were investigated 50 years ago in a configuration known as the Luce diode, in which collective acceleration of ions was studied. It was also known that the operation of the Luce diode is accompanied by a HPM burst, which was never measured. Results of experiments and simulations in various configurations based on a gridded vircator and dielectric reflectors confirm the existence of high-energy ion acceleration. Unfortunately, none of these configurations produce HPM of higher efficiency than a regular gridded vircator.

Collective Acceleration of Helium Ions from Its Residual Atmosphere in a Luce Diode

The collective acceleration of helium ions from its residual atmosphere in the Luce diode was studied at helium pressures from 0.13 to 0.23 Pa. The energy of accelerated ions was determined from the drift velocity of the virtual cathode accelerating the ions. The number of 4He was determined by radioactivities of 13N and 30P induced in h-BN and Al targets via the nuclear reactions 10B(α,n)13N and 27Al(α,n)30P. The efficiency of capturing 4He ions in collective acceleration from the residual helium atmosphere was estimated as 0.25%. With increasing helium pressure above 0.15 Pa, the energy of the main ion group noticeably decreased to 0.46 MeV/amu compared to the acceleration from a usual residual atmosphere (~0.6 MeV/amu); however, the probability of ion acceleration to a specific energy of up to 1.57 MeV/amu increased significantly. Such increases in the ion energy were accompanied by the appearance of the signal of the second virtual cathode 7–9 ns after the appearance of the first virtual cathode.

Effect of the residual atmosphere pressure on collective acceleration of ions in the Luce diode

Number and energy of protons and 12C ions collectively accelerated in the Luce diode were determined by radioactivation techniques for residual atmosphere pressure controlled from 5.5 Pa down to 12 mPa. We demonstrate for the first time that the reduction of pressure dramatically reduces average number of 12C ions with energy of up to 2.64eU/amu (U = 250 kV) but in turn increases number of protons accelerated to the same specific energies as well as it enables observation of protons with energies higher than 12eU. We suggest that the 2.64eU/amu protons and 12C ions are accelerated by the same relativistic electron bunches to equal velocities but 12C ions are directly captured in acceleration on the whole way of the bunches from the cathode to the target, while the protons are mostly extracted from the anode plasma.

A laser-driven droplet source for plasma physics applications

AbstractIn this paper, we report on the acceleration of protons and oxygen ions from tens of micrometer large water droplets by a high-intensity laser in the range of 1020 W/cm2. Proton energies of up to 6 MeV were obtained from a hybrid acceleration regime between classical Coulomb explosion and shocks. Besides the known thermal energy spectrum, a collective acceleration of oxygen ions of different charge states is observed. 3D PIC simulations and analytical models are employed to support the experiential findings and reveal the potential for further applications and studies.

Compact Induction Accelerator of Laser Plasma for Ion Energy up to 1 MeV

The collective acceleration of laser plasma ions in a rapidly increasing magnetic field (108 T/s) excited by a powerful current pulse in a low-inductive conical spiral expanding in the direction of plasma acceleration has been studied. A mathematical model and an algorithm for calculating the radial Br and axial Bz components of the magnetic field in the approximation of a conical spiral by a system of rings of variable radius are proposed to analyze the factors affecting the efficiency of such acceleration. Based on computer modeling and an experimental variation of magnetic-field excitation parameters, the regime of effective ion acceleration is obtained. With the help of time-of-flight collector measurements, the velocities of ions whose atomic mass differs by two orders of magnitude are determined. The maximum velocity of both light ions (lithium) and heavy ions (lead) exceeds 106 m/s, and the corresponding energy for lead ions is ~1 MeV. The efficiency of collective acceleration with the direct acceleration of laser plasma ions in a high-current high-voltage diode with magnetic insulation is compared.

Collective Acceleration of Ions in a Pulsed Magnetic Field of a Conical Spiral

The collective acceleration of laser plasma ions in a magnetic field generated by a powerful fast-growing current pulse in a low-inductive conical spiral is studied. The velocity of ions for a number of elements which significantly differ in atomic weight are obtained on the basis of collector measurements. The maximum velocity of both light (lithium) and heavy (lead) ions exceed the value of 108 cm/s; for ions of lead, the corresponding energy amounts to a value of ∼1 MeV. A mathematical model of ion acceleration is proposed and simulation results are compared with the experiment.

Numerical Simulation of Plasma Near the Cathode Spot of Vacuum Arc

Kinetic numerical simulation of plasma near the cathode spot (CS) was performed. Two types of possible solutions for the self-sustained CS on copper cathode were found. The firs type of solutions is valid for quasi-stationary spot with radius of about $100~\mu \text{m}$ . Stationary solution in this case is possible with cathode temperature 4.2–4.5 kK, current density $\sim 10^{6}$ A/cm2, and applied voltage 20–25 V. The second type of solution is obtained for the spot with radius of $1~\mu \text{m}$ and spherical geometry of plasma expansion. Possible solutions were obtained for the cathode temperature of above 6.2 kK, current density of about $10^{8}$ A/cm2 and applied voltage of 15–25 V. Transient simulations of the near-cathode plasma expansion have shown that if current density remains less than $10^{9}$ A/cm2 then the plasma expansion has a “quiet” self-similar character. At higher current density the plasma expansion has an essentially nonstationary character. The high-density current leads first to the development of Buneman instability and second to the plasma rupture with the creation of conditions for collective acceleration of ions toward the cathode and toward the anode. The accelerated ions create an additional powerful heat flux to the cathode, which should facilitate the reproduction of the CSs in the spark stage of vacuum discharge.

Collective acceleration of ions in picosecond pinched electron beams

Сharacteristics of intense electron–ion beams emitted by a high-voltage (280 kV) electron accelerator with a pulse duration of 200 ps and current 5 kA are studied. The capture phenomena and the subsequent collective acceleration of multi charged ions of the cathode material by the electric field of the electron beam are observed. It is shown that the electron–ion beam diameter does not exceed 30 µm therein in the case of lighter ions, and the decay of the pinched beam occurs at a shorter distance from the cathode. It is established that the ions of the cathode material Tin+ captured by the electron beam are accelerated up to an energy of ⩽10 MeV, and the ion fluence reaches 1017 ion cm−2 in the pulse. These ions are effectively embedded into the lattice sites of the irradiated substrate (sapphire crystal), forming the luminescent areas of the micron scale.

Creating Ti:Al2O3 media with pinched beams of electrons and Ti n+ ions

The collective acceleration of multiply charged titanium ions on pinched electron beams and the mechanisms of titanium ion implantation into sapphire crystals are studied. Efficient Ti3+ ion implantation is achieved by irradiating sapphire crystals with high current picosecond beams of electrons and Ti n+. The ions are shock-implanted into regular positions of the crystalline lattice, replacing Al3+ ions.

Motion of a virtual cathode in a cylindrical channel with electron beam transport in the “compressed” state

This paper studies the motion of a virtual cathode in a two-section drift tube with the formation and breakup of the “compressed” state of an electron beam. Experimental arrangements to intercept part of the injected current during the voltage pulse and to provide virtual cathode motion toward the collector are proposed. The arrangements were implemented on the SINUS-7 high-current electron accelerator. Theoretical and experimental dependences of the virtual cathode velocity on the injected current and cathode voltage are presented. The experimental data on virtual cathode motion agree with its theoretical model based on analytical solutions of equations assisted by computer simulation with the PIC code KARAT. The results of the work demonstrate the feasibility of controlling the virtual cathode motion which can be used in collective ion acceleration and microwave generation.

Controlled collective acceleration of electron-ion bunches

The fundamental possibility of a new method for controlled collective ion acceleration by electron bunches of high-current relativistic picosecond beams has been proved. Dense relativistically rotating electron bunches are formed using a cusp magnetic system by their capture in a special magnetic trap. An electron bunch is filled with ions when it interacts with a preliminarily prepared plasma bunch with a certain density. Then, the effective potential well of the magnetic trap is stepwise shifted synchronously with the motion of ions by means of a system of turns with controlled currents. This ensures the displacement and confinement of electrons in the direction of acceleration. The shift of the center of the well at each step is chosen such that ions are in the region of acceleration by a high self electric field of the electron bunch. In contrast to the known methods for collective acceleration, the proposed method makes it possible to avoid the mismatch of the electron and ion components of bunches, disruption of the acceleration of ions, and development of numerous instabilities, because the duration of the acceleration cycle is in the nanosecond range.

Fundamental difference between picosecond and nanosecond laser interaction with plasmas: Ultrahigh plasma block acceleration links with electron collective ion acceleration of ultra-thin foils

AbstractArguments are discussed on how ion energy measurements from ultra-thin diamond irradiation with 45 fs laser pulses of 26 terawatt power may be related to the ultra-high acceleration of plasma blocks where the significance of the highly efficient direct conversion of laser radiation into mechanical motion of ions or plasma blocks is dominated by nonlinear (ponderomotive) forces in fundamental contrast to thermo-kinetic dominated interaction with ns laser pulses.

Phenomenological model of the unstable stage of a vacuum spark discharge

A model of the unstable stage of a spark discharge in vacuum is proposed, which describes all typical manifestations of this stage, including current spikes in the diode, an increase in the potential at the cathode flame front, collective acceleration of ions in vacuum and plasma diodes, change in the cathode erosion mechanism, and the emergence of electron microbeams with a high current density at the anode. It is shown that these processes are associated with the formation of a charged electron layer of a spatially inhomogeneous plasma at the cathode flame boundary at the unstable stage of the spark discharge in vacuum. The emergence of this layer is associated with a limited emissive ability of the plasma at the cathode flame front during its expansion in vacuum. This leads to disruption of the plasma (field-induced emission of electron from the boundary region of the flame) and the formation of a short-lived charged plasma, viz., high-density ion cluster at the cathode flame boundary. The estimates obtained using this model are in good agreement with the experimental data on physical processes at the unstable stage of a vacuum spark discharge.

Model of Collective Acceleration of Ions in Spark Stage of Vacuum Discharge

A new mechanism of the collective acceleration of anomalous ions at the spark stage of a vacuum discharge is proposed. A 2-D electromagnetic particle-in-cell code was developed to study the mechanism. Computer simulation showed that ions are accelerated in the presence of a plasma cloud in the interelectrode gap, where the development of strong electron instability during the propagation of a cathode electron beam leads to potential buildup to a level exceeding the applied voltage. The appearance of the accelerated ions of the interelectrode plasma is accompanied by a jump in the diode current.

Collective acceleration of xenon ions in a plasma-anode vircator

The collective acceleration of xenon ions in a plasma-anode vircator is studied. It is shown that the energy of accelerated ions may reach 900 MeV. The image of a bremsstrahlung source on the target suggests effective transport of relativistic electrons in the drift channel.

Collective ion acceleration during the decay of a high-current Z-pinch

A study is made of the Z-pinch plasma expansion after the current is switched off. Measurements were carried out in experiments on the implosion of tungsten wire arrays in the Angara-5-1 facility. It is found experimentally that, at a distance of 2 m from the pinch, the ion velocity in the expanding Z-pinch plasma is about (2.5–4.0) × 107 cm/s, which substantially exceeds the thermal velocity of tungsten ions. A model describing the plasma expansion process is proposed that is based on the ambipolar acceleration mechanism. The results of numerical simulations are compared with the experimental data.

Scaling Laws for Collisionless Laser–Plasma Interactions of Relevance to Laboratory Astrophysics

Scaling laws for interaction of ultra-intense laser beams with a collisionless plasmas are discussed. Special attention is paid to the problem of the collective ion acceleration. Symmetry arguments in application to the generation of the poloidal magnetic field are presented. A heuristic model for evaluating the magnetic field strength is proposed.

Influence of the axial magnetic field on the current instability and on the collective acceleration of ions in plasma diodes

It is shown that, while suppressing transverse electron motion, the axial magnetic field with an induction of up to 6.8 × 10−2 T in the gap of a plasma diode has no significant effect on the current instability and on the acceleration of ions at electron beam currents of ≤40 A. The increase in both the critical current and the period of current oscillations is related to an increase in the plasma density after applying the magnetic field. The maximum energy of the accelerated magnesium ions decreases by ≈25% at an induction of 1.7 × 10−2 T and does not depend on the magnetic field in the range (1.7–6.8) × 10−2 T.