Injection Of Relativistic Electron Beam Research Articles

Intensification of laser-produced relativistic electron beam using converging magnetic fields for ignition in fast ignition laser fusion

The kilo-tesla-class converging magnetic field effects on the core heating properties and the energy and duration of relativistic electron beam (REB) required for ignition in fast ignition laser fusion has been evaluated by parametric 2D hybrid simulations where a uniformly compressed DT core with ρ = 300 g/cm3 is heated by REB with TREB = 3 MeV, IREB = 0.69 × 1020 W/cm2 and θREB = 40° under sufficiently strong magnetic field (Bext = 3 kT at the REB injection position). The kilo-tesla-class converging magnetic field can intensify REB and then enhances the core heating power drastically. As the results, the fusion ignition can be initiated by the REB with EREB ≧ 50 kJ and τREB = 10 ~ 30 ps. With increasing mirror ratio RM, the negative effect of converging field, i.e., mirror reflection, becomes significant, which enhances the REB energy required for ignition (EREB,ig = 49 kJ for RM = 3 → EREB,ig =77 kJ for RM = 20).

Influence of Plasma Unsteadiness on the Spectrum and Shape of Microwave Pulses in a Plasma Relativistic Microwave Amplifier

Dependence of the shape of a microwave pulse in a plasma relativistic microwave amplifier (PRMA) on the initial plasma electron density in the system is detected experimentally. Depending on the plasma density, fast disruption of amplification, stable operation of the amplifier during the relativistic electron beam (REB) pulse, and its delayed actuation can take place. A reduction in the output signal frequency relative to the input frequency is observed experimentally. The change in the shape of the microwave signal and the reduction in its frequency are explained by a decrease in the plasma density in the system. The dynamics of the plasma density during the REB pulse is determined qualitatively from the experimental data by using the linear theory of a PRMA with a thin-wall hollow electron beam. The processes in a PRMA are analyzed by means of the KARAT particle-in-cell code. It is shown that REB injection is accompanied by an increase in the mean energy of plasma electrons and a significant decrease in their density.

The Rod Degenerate Plasma-Rippled-Wall Waveguide and Its Excitation by Relativistic Electron Beam Injection

The dispersion relation of electromagnetic waves in a rippled-wall waveguide with a degenerate plasma column protected by an annular dielectric layer is theoretically investigated. By injecting a thin annular relativistic electron beam (TAREB) in the region between dielectric and metallic cylinders in the aforementioned configuration as an energy source, the excitation of terahertz (THz) electromagnetic waves is investigated. Also, the dependence of dispersion relation and time growth rate on the radius of the dielectric, the corrugation amplitude, and period is studied. Furthermore, it is found that the presence of the degenerate plasma rod in the rippled-wall waveguide leads to obtain high-frequency modes in the THz frequency region. Finally, the electric-field profiles in this waveguide are plotted.

New Results in the Theory of Multiple Mirror Plasma Confinement

Theory of plasma confinement in a multiple mirror trap is extended. Plasma lifetime is estimated for new regimes with partially devastated loss-cone, which occur at the stage of plasma decay in GOL-3 multiple mirror after termination of relativistic electron beam injection.

Application of Thomson Scattering System at 1.06 μm for Study of Plasma Density Dynamics at Multimirror Trap GOL-3

Thomson scattering system for measurements of radial profile of plasma density (range 0.5-5×1021 m-3) with temperature up to 2 keV was developed at the GOL-3 facility. First harmonics (λ=1.06 μm) of Nd glass laser is used. Scattered light from different points of plasma cross-section is imaged to a set of quartz optical fibers and detected by avalanche photodiodes.During the first 10 μs after start of the relativistic electron beam injection the intense light emission from plasma is observed. Single powerful laser pulse is used for providing of good signal-noise ratio in this period. Later the plasma radiation intensity decreases and the less powerful laser oscillator operated in multiple-pulsed regime is used.Description of the diagnostics, methodical aspects of operation, and results of the density dynamics measurements are presented in the paper.

Explanation of Turbulent Suppression of Electron Heat Transfer in GOL-3 Facility at the Stage of Relativistic Electron Beam Injection

The effect of the electron heat transfer suppression during the stage of relativistic electron beam injection into a plasma was discovered experimentally more than a decade ago. It is now widely adopted that the suppression is a side sequel of Langmuir turbulence excited by the beam, however neither quantitative theory nor even rough estimates of the phenomena were available so far. We argue that the coefficient of turbulent thermal conductivity can be evaluated from a robust judgement based on the energy balance consideration.

Relativistic electron beam injection from spacecraft: performance and applications

Linear accelerators (linacs), producing relativistic (5 MeV) electron beams are down to a size that allows them to be flown on spacecraft and sounding rockets. This opens up to new opportunities for atmospheric/ionospheric modification experiments where the mesosphere and lower thermosphere regions can be perturbed down to 40 km altitude. In this presentation, the relativistic electron beam injection process is investigated by means of 3-dimensional particle-in-cell (PIC) simulations to determine the initial interaction of the beam with the spacecraft and the ambient plasma. The results indicate, that relativistic beams are more stable than keV-energy beams investigated in the past, allowing the injection and propagation of beams with currents several orders of magnitude higher than for keV-energy beams. The superior stability of relativistic beams allows a large fraction of the energy to be deposited in the lower atmosphere. It is suggested that relativistic beams can be applied to investigations of atmospheric electrical and chemical processes.

Particle simulations of relativistic electron beam injection from spacecraft

Linear accelerators producing relativistic (5 MeV) electron beams are now down to a size that allows them to be flown on spacecraft and sounding rockets. This opens up new opportunities for atmospheric/ionospheric modification experiments where the mesosphere and lower thermosphere regions can be perturbed down to 40‐km altitude. In this paper the relativistic electron beam injection process is investigated by means of three‐dimensional particle‐in‐cell simulations to determine the initial interaction of the beam with the spacecraft and the ambient plasma. The results indicate that relativistic beams are more stable than keV‐energy beams investigated in the past, allowing the injection and propagation of beams with currents several orders of magnitude higher than those for keV‐energy beams. The superior stability of relativistic beams is the result of a combination of effects including the higher relativistic electron mass, a lower beam density, and a smaller effect from spacecraft charging. Relativistic beams injected downward from spacecraft are therefore expected to deposit a large fraction of the energy in the middle atmosphere. In the high‐current limit (I > 100 A) the beam self‐fields are strong. In this regime a beam may propagate in the ion‐focused regime, where beam electrons expel ambient electrons to create a channel of ambient ions that space charge neutralize the beam. The establishment of the ion channel, however, creates significant turbulence and scattering.

Interhemispheric transport of relativistic electron beams

Relativistic electron beam injection simulation results are presented from a new interhemispheric transport model, with a spatial domain reaching from 90 km to 90 km in the conjugate ionospheres. A single beam pulse is injected upward at 700 km during the first time step (10−4 s) and allowed to scatter and decay through collisional interactions with neutral particles and the core plasma. The maximum pulse duration for collisional processes to prevail over the wave‐beam instabilities is estimated, and the assumed pulse length is well within this limit. For an L=2 field line, the e‐folding time of a 5 MeV beam is 265 s, which is much bigger than the bounce period (0.19 s) and comparable to drift period around the Earth.

Plasma confinement studies in open systems

Studies in open systems in the world are reviewed from viewpoints of the potential confinement and magnetohydrodynamic (MHD) stability. The tandem mirror GAMMA 10 has shown the potential confinement of a high-ion-temperature plasma from an analysis of the time evolution of end-loss ion current and end-loss ion energy distributions. The central cell density was increased by 50% by the potential confinement. In the HIEI tandem mirror H-mode-like phenomena were observed with an increase in density and diamagnetic signal in a limiter biasing experiment. Potential formation phenomena in plasmas are studied by -like Upgrade under different magnetic field configurations and plasma conditions. The fully axisymmetric tandem mirror AMBAL-M is under construction and its end mirror system has been assembled. Heating experiments of a plasma gun produced plasma by neutral beam injection and ICRF heating are in progress. The gas dynamic trap (GDT) experiment has successfully produced an MHD-stable high-temperature, high-density plasma. In GOL-3-II, a high-density plasma with several 100 eV temperature is created by powerful relativistic electron beam injection. Construction of HANBIT has been completed and experiments on plasma production and ICRF heating have begun.

Relativistic electron beam generation in a plasma-filled diode with foilless injection into a dense plasma

In the experiments an relativistic electron beam (REB)-plasma interaction, the foilless injection of REB from a magnetized diode is of special interest due to the low spread angle of the beam and high repetition rate of the shots. In the experiments presented, the problem of diode shortening in the presence of a dense plasma from the interaction chamber has been solved using a special drift pipe as an anode of the foilless diode. The electron beam (U/sub d//spl sim/0.7 MeV, t/sub b//spl sim/100-200 ns) produced by an axially symmetric magnetically insulated diode has been injected into a magnetized hydrogen plasma column with density ranging from 1/spl middot/10/sup 15/-3/spl middot/10/sup 16/ cm/sup -3/. It has been found that the anode pipe substantially reduces the plasma flow into the diode gap, but does not stop it completely, thus the REB generation in a plasma-filled diode has taken place. In some regimes of the beam generation it becomes possible to increase significantly the injected current and total energy deposition of the beam in comparison with the case of a vacuum magnetized diode of the same geometry. The experiments have shown effective dense plasma heating under the foilless injection.

Macroscale particle simulation of relativistic electron beam injection into a magnetized plasma channel

A large-scale particle simulation of an intense relativistic electron beam injection into a longitudinally periodic and magnetized, three-dimensional plasma channel is performed with application to the steady-state current drive of tokamaks. It is found that the electromagnetically beam-induced electric field uniformly decelerates the beam electrons and generates a plasma return current as far as the injection continues. The beam electrons are decelerated also by the scaler potential field especially before the beam path becomes closed. A net longitudinal current, and hence the azimuthal magnetic field, is formed in the vicinity of the beam path after the return current has reached a steady force–balance equilibrium with the electric field and anomalous friction. The net saturation current is independent of the injection beam current and is scaled as Inet∼(γ2−1)1/2, where γ=(1−v2b/c2)−1/2 and vb is the velocity of the electron beam. For γ≫1, a macroscale helical instability develops and prevents the net current from reaching the level given by the aforementioned scaling. This instability is suppressed by application of a strong longitudinal magnetic field, which recovers the net current of the previous scaling.

Conceptual Design of a Movingring Reactor: Karin-I

A 650-MW(electric) deuterium-tritium fusion reactor, KARIN-I, has ten moving plasma rings, which are produced by relativistic electron beam injection, heated by a major radius compression, and transported into a linear cylindrical burning section by annularly flowing liquid lithium outside the silicon carbide first wall. The liquid lithium not only stabilizes the tilting motion of the rings but also works as the tritium breeder and the main coolant. Energy from the ash-accumulated rings is efficiently recovered at the exit during the major radius expansion. The linear alignment of reactor components ensures easy assembly and disassembly, and also provides for easy maintenance. These features of the reactor result in a net electric output power of 650 MW(electric) with overall plant efficiency of 30%.

Intense relativistic electron beam ring (SPAC)

Experiments carried out at Nagoya since 1973 have shown that the injection of relativistic electron beams (REB) into toroidal devices can lead to a variety of magnetic field configurations having q-values ranging from q = 0 to q = 7. Among them, the REB ring-core configuration is a spherator-like configuration characterized by the presence of a REB and a currentless plasma confinement region outside the core.

Relativistic electron beam injection into neutral gases

Relativistic Electron Beam (REB) (UD approximately=1 MV, Ib approximately=10 kA, tau b=60 ns) injection into gases (He, SF6, He+SF6+H2 mixture and air) in a wide pressure range 1-750 torr (for air 10-3-750 torr) is investigated experimentally. The maximum energy loss of REB in SF6 at P0 approximately=750 torr had order of 1090 Joules (about 40% of the beam energy) and the maximum degree of the beam current compensation by the return current of the order of 0.8 was obtained in the He at P0 approximately=1 torr. The conditions for RE current transportation of the order of 0.85-0.99 through the drift chamber with the length approximately=120 cm are found. All experimental results at the high gas pressures may be explained by the classical theory of single particle REB-gas interaction. In the low gas pressure range the collective effect of interaction become important.

REB Injected Toroidal Plasma

A stable relativistic electron beam (REB) ring for plasma confinement was formed by REB injection with the help of image currents in a resistive shell, and then the ring was compressed in major radius by a factor 2.0. The current rise well obeyed the adiabatic scaling law.

On the injection of a cold relativistic electron beam into a cold plasma

In a one-dimensional model the initial phase of the injection of a relativistic electron beam into a plasma is studied, both analytically and computationally. We find that in a time of a few beam plasma periods the beam obtains a “temperature” which is much higher than expected from the analytic treatment.

Injection of high-current relativistic electron beams into plasma and gas

A review is given of theoretical and experimental papers on the injection of high-current relativistic electron beams into plasma and neutral gas. The review begins with work on the equilibrium configurations of electron beams which are partially or completely neutralized in current and charge; limiting beam currents which can be achieved in different equilibrium configurations are determined. The establishment of equilibrium during the injection of relativistic electron beams into plasma and neutral gas is discussed next. In the case of injection into plasma, particular attention is paid to the neutralization of charge and current, whilst in the case of injection into neutral gas the ionization of the latter and the capture and acceleration of the resulting ions in the space-charge field on the leading front of the beam are also discussed. The results of experimental studies are given and are compared with existing theoretical descriptions.

Injection of relativistic electron beams with arbitrary radial profiles into warm collisional plasmas

The results of previous authors for the injection of relativistic electron beams into unmagnetized collisional plasmas are generalized by allowing for arbitrary radial beam profiles and finite electron temperature. For nu t' >1 (R=beam radius) the return current has diffused out of the beam and magnetic shielding is lost. For beam currents well above the Alfven current the beam pinches before reaching tD. For beams with currents from 1 to 100 times the Alfven current and with n'/ne=10-1 or 10-3 (n'=beam density, ne=plasma density) critical times for which the beam is seriously affected or destroyed by pinching are calculated numerically. A parabolic and a step function profile are used for comparison and the critical times are found to be only weakly dependent on the profile. The return current heating time, which determines the maximum free path of the beam, is also calculated.

Difficulties with injection of relativistic electron beams into toroidal fusion devices

It is shown that neither E × B drift nor diamagnetic beam configurations allow injection of externally generated strong relativistic electron beams into fusion devices for the purpose of plasma heating.