2.5-Dimensional numerical simulation of a high-current ion linear induction accelerator

Results are presented from numerical particle simulations of the transport and acceleration of a high-current tubular ion beam through one to five magnetically insulated accelerating gaps. The ion beam is neutralized by an accompanying electron beam. The possibility of transporting a high-current neutralized ion beam through five cusps is demonstrated. It is shown that the quality of the distribution function of a high-current ion beam at the exit from the accelerator can be substantially improved by optimizing the energy of the neutralizing electron beam. It is also shown that, by injecting additional high-current electron beams into the cusps, the accelerated ion beam can be made more monoenergetic and its divergence can be reduced.     

Low-frequency instability of an ion beam in the field of a high-current REB

A study is made of the linear and nonlinear stages of the low-frequency instability of an ensemble of ions that execute radial oscillations in the electric field of the space charge of an unneutralized high-current relativistic electron beam. Nonlinear mechanisms for stabilizing the low-frequency ion instability are considered. It is shown, in particular, that, under certain conditions, the development of the low-frequency instability can lead to the ejection of ions onto the walls of the drift chamber.     

Self-consistent electron and ion motion in a high-current plasma channel

The problem of self-consistent motion of charged particles in a high-current plasma channel is solved using the kinetic model of a plasma with electron and ion beams whose motion is governed by the resulting electromagnetic field. It is shown that, in a high-density plasma, the ion motion makes the contribution of electrons to the current in the channel negative, in which case the ion current is higher than the net current and the plasma moves at a high speed as an electrically neutral axial stream whose direction coincides with the direction of the current in the channel.     

The use of a high-current electron beam in plasma relativistic microwave oscillators

Relativistic microwave electronics faces the problem of using high currents of relativistic electron beams; i.e., it is possible to use beams the current of which is lower than that of actually existing high-current accelerators. We show the possibility of increasing the power of radiation generated in a plasma relativistic microwave oscillator (PRMO) due to an increase in the absolute value of current. For the beam currents close to the value of limiting vacuum current, the efficiency of microwave generation decreases; therefore, we study PRMO schemes with a high value of limiting vacuum current, i.e., schemes with a small gap between a hollow relativistic electron beam and the waveguide wall. The results of the experiment and numerical simulation are discussed.     

Focusing of heavy ion beams by a high-current plasma lens

Results are presented from studies of the focusing of wide-aperture low-energy (100–400 eV) and moderate-energy (5–25 keV) beams of heavy-metal ions by a high-current electrostatic plasma lens. It is found experimentally that, because of the significant electron losses, the efficient focusing of such beams can be achieved only if the external potentials at the plasma-lens electrodes are maintained constant. Static and dynamic characteristics of the lens are studied under these conditions. It is shown that, as the beam current and the electrode voltage increase, the maximum electrostatic field in the lens tends to a certain limiting value because of the increase in the spatial potential near the lens axis. The role of spherical and moment aberrations in the focusing of wide-aperture low-divergence ion beams is revealed. It is shown that, even when spherical aberrations are minimized, unremovable moment aberrations decrease the maximum compression ratio of a low-energy heavy-ion beam because of the charge separation of multiply charged ions in the focal region. At the same time, as the ion energy increases, the role of the moment aberrations decreases and the focusing of high-current heavy-ion beams by a plasma lens becomes more efficient than the focusing of light-ion (hydrogen) beams. This opens up the possibility of using electrostatic plasma lenses to control ion beams in high-dose ion implanters and high-current accelerators of heavy ions.     

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.     

Deep modulation of a high-current relativistic electron beam in a system of coupled cavities

The excitation of inphase (0-type) and antiphase (π-type) electromagnetic oscillations by a relativistic electron beam in a system of identical coupled cavities is considered. It is shown that, in the case of excitation of antiphase oscillations, instability develops in a shorter system of cavities than it does when inphase oscillations are excited. In the nonlinear stage of the excitation of antiphase oscillations in a system of coupled cavities, a virtual cathode forms that breaks the initially uniform relativistic electron beam into a periodic sequence of spatially separated short bunches.     

SOS induction by vacuum,desiccation and low-energy ion beam mock-irradiation in bacteria

In this work, we compared the SOS response induced by vacuum-drying, desiccation (wind-spray-drying) and low-energy ion beam mock-irradiation with that of mitomycin C, UV induction. The induction factor induced by vacuum-drying and low-energy ion beam mock-irradiation was relatively higher than that of desiccation in Sa194 and JC19008 strain, respectively. These findings revealed that the SOS response produced by low-energy ion beam mock-irradiation was mainly induced by the step of vacuum-drying, unlikely by the step of wind-spray-drying. The mutation frequencies of rifampicin resistance gene in AB1157 andlacI gene in W3110 increased significantly by vacuum treatment and low-energy ion beam mock-irradiation, but had no remarkable change by desiccation treatment. Meanwhile, the mutation frequency of rifampicin resistance gene in 1C400 strain was not significantly influenced by these treatments. These results implied that the SOS response played an important role in the mutations induced by vacuum treatment and low-energy ion beam mock-irradiation.     

Study of the possibility to control ion generation and transport in a high-current vacuum spark

The possibilities of optimizing a high-current vacuum spark as a source of metal ions are discussed. The influence of the shape and size of the electrodes on both the depth to which the hot plasma region is immersed in the surrounding cold matter and the plasma state in the hot spot, which is the source of multicharged ions, is demonstrated. Methods for optimization of the design of the discharge device for increasing the ion yield from a high-current vacuum spark are considered.     

An annular high-current electron beam with an energy spread in a coaxial magnetically insulated diode

An elementary theory of an annular high-current electron beam in a uniform transport channel and a coaxial magnetically insulated diode is generalized to the case of counterpropagating electron beams with a spread over kinetic energies. Expressions for the sum of the absolute values of the forward and backward currents in a uniform transport channel and for the flux of the longitudinal component of the generalized momentum in a coaxial magnetically insulated diode as functions of the maximum electron kinetic energy are derived for different values of the relative width of the energy distribution function. It is shown that, in a diode with an expanding transport channel and a virtual cathode limiting the extracted current, counterpropagating particle flows are established between the cathode and the virtual cathode within a certain time interval after the beginning of electron emission. The accumulation of electrons in these flows is accompanied by an increase in their spread over kinetic energies and the simultaneous decrease in the maximum kinetic energy. The developed model agrees with the results of particle-in-cell simulations performed using the KARAT and OOPIC-Pro codes.     

Mutant induction in gametophytes of Undaria pinnatifida (Phaeophyceae) by heavy ion beam irradiation

Undaria pinnatifida, the brown macroalga, is a major commercial edible seaweed, and there is increasing interest in breeding new, improved cultivars for market expansion. In this study, we attempted to establish mutagenesis in U. pinnatifida using Ar and C ion beams as mutagens to meet future demands. To screen irradiated generations for mutants, U. pinnatifida zoospores irradiated with Ar and C ion beams were cultivated in plastic Petri dishes. Some gametophytes derived from the irradiated zoospores showed growth arrest or cell death at the initial developmental stage. Although the growth inhibition and lethal effects were observed at high doses of each ion irradiation, the Ar ion irradiation had high biological effects on cell division and growth. The gametophytes that showed a reduction in cell elongation were designated as an inhibited cell elongation mutant. A comparison of the mutant induction frequencies revealed that the C ion beam showed a higher frequency than the Ar ion beam. The highest frequency was 0.83% at 12.5 Gy of the C ion beam. We determined the total number of sporophytes and embryos per female gametophyte after sporophyte induction. High‐dose irradiation with the Ar ion beam decreased the embryo and sporophyte formation, suggesting that the Ar ion beam also has exhibited high biological effects on the fertilization or embryogenesis processes or both. The developed heavy ion mutagenesis and mutant screening methods would be useful for mutation breeding and constructing specific mutant libraries in brown algae, and not only in U. pinnatifida.     

Mechanisms for the formation and transport of ion fluxes in the plasma of a high-current vacuum spark

The processes of ion flux formation in the plasma of a high-current vacuum spark were investigated experimentally. It is shown that multicharged ions are generated in the neck formed in the erosion products of the inner electrode. The plasma escaping from the neck region plays a role of a piston dragging particles of the cold peripheral plasma into ambient space. As the discharge current increases, the flux of the evaporated electrode material grows, the degree of ionization of the plasma produced decreases, and the efficiency of plasma heating caused by the pinching effect is reduced.     

Interaction of a high-current electron beam with hybrid waveguide and plasma modes in a dielectric Cherenkov maser with a plasma layer

The characteristics of a high-current electron beam-driven microwave amplifier—a dielectric Cherenkov maser—are investigated in the framework of linear theory for the case of a plasma layer present at the surface of the maser slow-wave structure. The dispersion relation for axisymmetric perturbations is obtained for the conventional configuration (a circular dielectric-lined waveguide and a thin annular beam propagating within the vacuum region inside the annular plasma) in the model of a fully magnetized plasma and beam. The results of numerically solving the dispersion relation for different beam and plasma parameters are presented, and an analysis based on these results is given with regard to the features of the beam interaction with the hybrid waves of the system (both hybrid waveguide and hybrid plasma modes). For the hybrid waveguide mode, the dependences of the spatial growth rate on the frequency demonstrate an improvement in the gain at moderate plasma densities, along with narrowing the amplification band and shifting it toward higher frequencies. For the hybrid plasma mode, the interaction with a mildly relativistic (200–250 keV) beam, when the wave phase velocity is close to the speed of light in the dielectric medium, is most interesting and, therefore, has been studied in detail. It is shown that, depending on the beam and plasma parameters, different regimes of the hybrid plasma mode coupling to the hybrid waveguide mode or a usual, higher order plasma mode take place; in particular, a flat gain vs. frequency dependence is possible over a very broad band. The parameters at which the ?3-dB bandwidth calculated for the 30-dB peak gain exceeds an octave are found.     

Experimental observation of electron beam generation in the paraxial region of a high-current discharge due to a pinch effect

The phenomenon of “runaway” of electrons in the paraxial region of a Z-pinch discharge in the heavy element environment has been experimentally observed using the methods of pulsed optical shadowgraphy, X-ray pinhole imaging, and time-of-flight measurements.     

Radiobiological effects of a low-energy ion beam on wheat

The radiobiological effects of a low-energy nitrogen ion (N⁺) beam on wheat were studied, particularly with regard to the induction of chromosome aberrations. The results demonstrated that the three test varieties showed different sensitivities to ion implantation, and a higher dose of ion implantation had a marked effect on the germination and survival rate of the seeds exposed. The germination rate and survival rate curve basically followed a similar trend in the same variety. Cytological analysis indicated that ion beams were effective in producing chromosome aberrations. The frequencies of mitotic or meiotic cells with chromosome aberrations increased linearly with increasing doses. The aberration types included, for example, acentric fragments, chromosome deletions, lagging chromosomes, chromosome bridges and micronuclei. In the root tip cells, aberrations chiefly consisted of acentric fragments and deletions. Chromosome bridges and lagging chromosomes were the main aberration phenomena observed in the pollen mother cells. The highest frequencies of root tip cells and pollen mother cells with chromosome aberrations were 15.2% and 39.8%, respectively. Changes in morphology and mutant were also observed in the plants derived from exposed seeds. Received: 10 April 2000 / Accepted: 10 October 2000     

Influence of the electrons reflected from the collector on the parameters of a high-current relativistic electron beam

In plasma microwave oscillators, electrons fall onto the surface of a graphite collector, which leads to the generation of secondary electrons. The influence of the electrons reflected from the collector on the parameters of a high-current relativistic electron beam propagating in a strong longitudinal magnetic field was studied experimentally and by numerical simulations. It is shown that the penetration of the reflected electrons into the drift space can lead to a substantial increase in the depth of the potential well in the drift space, a decrease in the velocity of the beam electrons, and a broadening of the electron energy distribution function.     

Dynamics of ion heating in a gas-dynamic trap during neutral beam injection

The dynamics of the ion temperature of the target plasma in a gas-dynamic trap during high-power neutral beam injection is measured by using the Rutherford scattering technique. A comparison of the experimental results with the results of simulations by a model based on the theory of pair Coulomb collisions indicates no significant anomalous losses from the ion plasma component.     

Process of compensation of the space charge of a negative ion beam in a gas

The process of compensation of the space charge of a negative ion beam propagating through a neutral gas is investigated numerically. A comparison of the results obtained with experimental data unambiguously proves that, at high gas pressures, when the beam space charge is overcompensated, the electric field within the beam is determined by Coulomb collisions of the beam ions with plasma electrons. At low pressures, when the space charge is undercompensated, the field within the beam is determined by the dynamic processes related to oscillations of the beam current.     

Acceleration of impurity ions in the coulomb explosion of a relativistic spherical cluster with a complex ion composition

A semi-analytical model of the acceleration of light impurity ions to relativistic energies in the Coulomb explosion of a spherically symmetric homogeneous microtarget (cluster) consisting of ions of two types has been proposed. The spatiotemporal and spectral characteristics of accelerated impurity ions, which have a quasi-monochromatic spectrum, have been determined. The properties of high-energy impurity ions have been studied as functions of the total charge of the cluster and its ion composition.     

Vortex electron dynamics in a high-current plasma lens

An analytic study is made of the following problems: the instability of a plasma against the excitation of vortex turbulence, the turbulence saturation amplitude, the types and spatial structures of the nascent vortices, and their nonlinear growth rates in an electrostatic plasma lens for focusing high-current ion beams.