The explosive growth of electron temperature, produced by microwave heating of a collisional magnetoplasma in the vicinity of Langmuir resonance, is illustrated. This explosion is localized near by the irradiated surface of plasma volume. Such effect is stipulated by an external magnetic field, herein this field may be weak enough.

The properties of ion phase-space vortices are reviewed with particular attention to their role in the formation of small amplitude double-layers in current-carrying plasmas. In a one-dimensional analysis, many such double-layers simply add up to produce a large voltage drop. A laboratory experiment is carried out in order to investigate the properties of ion phase-space vortices in three dimensions. Their lifetime is significantly reduced as compared with similar results from one-dimensional numerical simulations of the problem.

This paper presents a survey of selected results of laboratory experiments and numerical simulations of plasma double layers. Emphasis is given to discrimination between features peculiar to the experimental or numerical investigation and results which may have general implications for double layers in space similar to that of laser or particle beam produced plasma. The discussion concentrates on certain aspects pertaining to dynamics, structure, and stability of double layers considering the effects of boundary conditions (trapped particles, Bohm conditions, and applied potentials), waves and turbulence, collisions, and volume ionization.

The mechanism of deflection of pulsed annular ion beams by toroidal magnetic fields is investigated. It is found that the ions of the annular beam obey the single particle orbits in the toroidal field. The polarization electric field, which is measured with an electric double probe in the annular beam inside the toroidal field, is found to be smaller than 1/10 of the value necessary for the force cancelling. It is reasonably concluded that the short-circuiting occurs via the toroidal magnetic field lines of force that have some rotational transform resulting from the helical winding of the toroidal coil.

Recent progress in research on Light Ion Beams-Inertial Confinement Fusion (LIB-ICF) at ILE, Osaka University is summarized. We report on pulsed power compression using PEOS, a super high voltage source, on diode physics, on beam trajectory control for focusing, on beam-target interactions and on a conceptual reactor design (Rokko I) in this article.

The phase diagram of high density (1023 ˜ 1027/cm3) deuterium is obtained by calculation. The values of specific heat, electrical resistivity and thermal conductivity in the metallic state are estimated over a wide range of temperature (10−2 ˜ 104 eV). The temperature dependences of these properties are shown in figures with the density. When T ≤ Tf (Tf: the Fermi temperature of electrons), the behavior is very similar to those of normal metals. At high temperatures where T ≥ Tf, the behavior is similar to that of completely ionized classical plasma.

This fundamental data for deuterium will help us understand the properties of fuel in inertial-confinement fusion and to solve the fluid equations for efficient compression of fuel pellets.

A conical-pinched electron-beam diode has been studied with the objective of increasing the brightness of this inherently high current ion beam. Experiments and calculations are described that suggest it may be possible to obtain powers as high as 1013W/cm2 at 4MV from a carefully designed insulated-anode-type pinched-electron beam diode.

The evolution processes of double-layers have been studied in a series of laboratory experiments using a triple plasma device. It was found that the existence of virtual cathode type potential wells at the electron injection boundary was the dominant triggering mechanism. The rapid growth of the potential well led to collisionless ion trapping and the establishment of the necessary trapped ion population. For double layers with small potential drops, collisionless ion trapping actually induced ion–ion streaming instabilities and the formation of ion phase-space vortices. In this regime, the system often exhibited relaxation type oscillations which corresponded to the disruption and the recovery of the double layers.

A linear parametric theory of laser light instabilities including decay, stimulated Raman and Brillouin scattering, etc. is currently well developed. However, attention is drawn to a novel laser light instability against parametric excitation of magneto-static fluctuations. In a collisionless plasma regime, magneto-static fields are driven by the ponderomotive electron magnetization current. Generally, two types of magneto-static instabilities exist: magneto-modulational instability and stimulated magneto-static scattering instability. Growth rates are calculated which indicate the possible importance for high laser intensity driven hot plasma regimes.

The current-neutralization fraction of a rotating and propagating light ion beam (LIB) injected into a low density plasma is investigated numerically. The beam space charge is essentially neutralized by a redistribution of the background plasma electrons in a time duration equal to the inverse of electron plasma frequency. When the density of the background plasma is comparable with that of the beam, incomplete current neutralization occurs because the strong magnetic field induced by the intense ion beam restricts the return plasma current.

In the simulation, the ion beam and the background plasma are treated as the fluids coupled with Maxwell's equations and Ohm's law, including the effect of the magnetic field on electrical conductivity. The calculations assume that the ion beam is injected in an unsteady fashion into the uniform plasma. It is found that the return current strongly depends on the density of the background plasma. The beam deceleration and the acceleration of the beam head and tail are also considered.

The free expansion of a heated mass of uniform gas (e.g. a laser produced plasma) can be modelled by self-similar motion with a linear velocity gradient. Using a series of numerical solutions we have shown that a reasonable representation is obtained by the use of a matching parameter relating the scale lengths in the prototype and its model, and that the representation improves as the ratio of the heating and disassembly times increases. In this paper we re-examine these two inferred results, and re-derive them on an analytic basis. The extension of the theory to multi-structured bodies shows that such systems of symmetric form allow self-similar motion, as does the particular case of an asymmetric one-dimensional foil. The case of isothermal foils is examined in detail to illustrate the derivation of the matching conditions.

Various mechanisms for driving double layers in plasmas are briefly described, including applied potential drops, currents, contact potentials, and plasma expansions. Some dynamic features of the double layers are discussed. These features, as seen in simulations, laboratory experiments and theory, indicate that double layers and the currents through them undergo slow oscillations, which are determined by the ion transit time across an effective length of the system in which the double layers form. It is shown that a localized potential dip forms at the low potential end of a double layer, which interrupts the electron current through it according to the Langmuir criterion, whenever the ion flux into the double is disrupted. The generation of electric fields perpendicular to the ambient magnetic field by contact potentials is also discussed. Two different situations have been considered; in one, a low-density hot plasma is sandwiched between high-density cold plasmas, while in the other a high-density current sheet permeates a low-density background plasma. Perpendicular electric fields develop near the contact surfaces. In the case of the current sheet, the creation of parallel electric fields and the formation of double layers are also discussed when the current sheet thickness is varied. Finally, the generation of electric fields (parallel to an ambient magnetic field) and double layers in an expanding plasma are discussed.

As the input power and energy content of Tokamaks are increased, the erosion rate of the first wall becomes larger, and a thick coating or cladding of low atomic number (Z) materials will be needed. Recently, the present authors prepared Si3N4–SiC films at alow temperature of 400°C by a plasma CVD method for the application to coating materials having high strength and wear resistance on metals and glasses. In this study, irradiation damage of the Si3N4–SiC films and 316 stainless steel (SUS-316) was investigated for the application to the first wall materials in a fusion reactor. The damage studies employed an intense pulsed light-ion beam (LIB) from the “ETIGO-I” device.

Nonmonotonic plasma potential structures are a common feature of many double layers and sheaths. Steady state plasma potential wells separating regions having different plasma potentials are often found in laboratory experiments. In order to exist, such structures all must find a solution to a common problem. Ions created by charge exchange or ionization in the region of the potential well are electrostatically confined and tend to accumulate and fill up the potential well. The increase in positive charge should eliminate the well. Nevertheless, steady state structures are found in which the wells do not fill up. This means that it is important to take into account processes which ‘pump’ ions from the well. As examples of ion pumping of plasma wells, we consider potential dips in front of a positively biased electron collecting anode in a relatively cold, low density multidipole plasma. Pumping is provided by ion leaks from the edges of the potential dip or by oscillating the applied potential. In the former case the two dimensional character of the problem is shown to be important.

The research of particle beam fusion and its related problems at The Institute of Atomic Energy in Beijing is evolving along the following five directions: 1. Pulsed power technology. An 80 GW intense electron beam accelerator has been built. Switch research is ongoing. 2. Diode research. The experimental research and theoretical simulation of electron pinch in the diode have been carried out. The pinch process has been investigated by measuring the area collapsing velocity of the pinching electron ring on the anode surface. Expanding velocities of the cathode and anode plasmas have been observed. The diode with large area cathode of 38 × 5 cm2 can produce a 46 kA electron beam current with a beam cross-section of 36 × 4 cm2 and good uniformity for pumping of a KrF laser. 3. Energy deposition of the electron beam on the targets has been studied by means of measurements of the intensity of soft X-rays, the energy spectrum of blow-off ions, the visible light spectra and the rear surface velocity of the target. These experiments show that the results are in agreement with the classical interaction mechanism for high Z targets, but it is several times higher than the classical result for low Z targets. 4. Electron beam propagation in neutral gases with various pressures space-and current-neutralization processes have been investigated. 5. The production of a KrF laser pumped by an electron beam. A laser beam with an energy of 13 J and pulse duration of 70 ns has been obtained.

A harmonic generator of submillimeter wavelength radiation, operating on a relativistic electron beam, is proposed. The device is shown to operate on principles of parametric interactions, under the particular conditions of an electric-quadrupole pump field which is propagating synchronously with the electron beam. Using a fluid model, it is shown that a cascade of parametric sum and difference frequencies in the transverse beam modes should occur, with each harmonic component growing convectively along the beam. The physical effect, termed the “sonic condition”, has been observed previously on a non-relativistic device emitting output radiation in the UHF range. A realization for relativistic beams is proposed, using an FEL structure as the parametric pump, a closed waveguide synchronous pump region and an output coupling of the gyrotron type. Possible advantages over the present state-of-the-art for high-power submillimeter electron-beam devices are discussed.

A Genuine two-fluid model of plasmas with collisions permits the calculation of dynamic electric fields and double layers inside plasmas including oscillations and damping. For the first time a macroscopic model for coupling of electromagnetic and Langmuir waves was achieved with realistic damping. Starting points were laser produced plasmas showing very high dynamic electric fields in nonlinear force produced cavitons and inverted layers, in agreement with experiments. Applications for any inhomogeneous plasma as in laboratory or in astrophysical plasmas can then be followed up by a transparent hydrodynamic description. We find the rotation of plasmas in magnetic fields and a new second harmonic resonance. Explanation of inverted double layers, second harmonic emission from laser produced plasmas, and laser acceleration of charged particles by the very high fields of the double layers is given.

Experimental results are reported on an extractor for pulsed, high-intensity beams of intermediate mass ions. Aluminum and indium plasmas were generated using a metal vapor vacuum arc. A method for electrostatic separation of ions from electrons at the anode was utilized to generate constant current beams, insensitive to plasma flux variations.

A maximum extraction voltage of 30 kV was applied across a 1·6 cm gap. Voltage pulse length ranged from 10 to 50μsec. Peak current densities of 15 mA/cm2 and normalized emittance of εn<3χ10-7; π-m-rad were achieved for Al+ and In+ from a 20-cm2 anode. Ions were predominantly in the +1 ionization state with no observable species contamination. The technology may have application to the induction linac approach to Accelerator Inertial Fusion.

1½ D computer simulations have been performed to illustrate the influence of ion dynamics on stimulated Raman scattering in laser irradiated plasmas. A flat density profile has been used. Backward and forward scatter and heated electron distribution have been studied as a function of ion mass and ion temperature. The results show clearly that the lighter the ions, the more inhibited the Raman scatter and associated fast electron production. Futhermore, when ions are cold enough to allow Brillouin scattering release, Raman scatter, as well as associated suprathermal electrons is even more reduced. These observations evidence the complex non-linear coupling of the electron plasma waves driven by the Raman instability and the ion fluctuations which can exist in the plasma.

Pinched electron beams emit high power microwaves by formation of a virtual cathode. Radiation occurs simultaneously with pinching or slightly thereafter. Observations of strong electrostatic fields and the partitioning of current into reflexing and transmitting populations at the same time that microwaves are emitted indicate virtual cathode formation. Microwaves originate mainly from the virtual cathode side of the anode. A two-dimensional model for the electron flow in the presence of a virtual cathode is presented. The model allows for electron reflexing and velocity distribution spread. Solutions with strong radial flow agree closely with microwave measurements, and result in the microwave frequency scaling linearly with diode current.