Generation of a homogeneous plasma in a glow discharge with a hollow anode and a wide-aperture hollow cathode

The principles for designing electrode systems for sources of ion beams of large cross section on the basis of a glow discharge are considered, and a system with combined magnetic and electrostatic confinement of the fast electrons in a wide-aperture hollow cathode and the generation of an ion-emitting plasma in the anode cavity is proposed. It is shown that the system investigated generates a plasma with a nearly homogeneous distribution of the ion emission current density at low gas pressures and can be effectively used to obtain ion beams over a broad range of energies. Pis’ma Zh. Tekh. Fiz. 25, 83–88 (June 26, 1999)     

Dynamics of the anode plasma in the magnetically insulated diode of the COBRA ion accelerator by modified laser deflectometry

A new type of optical system for measurements of laser beam deflection has been developed and implemented experimentally. The refractive index gradient in the anode plasma of a megavolt magnetically insulated diode in a high-power ion accelerator has been measured with submicron resolution. The refractive index distribution in the layer was measured during the pulse and the average electron density in the layer was determined. Pis’ma Zh. Tekh. Fiz. 23, 63–68 (May 26, 1997)     

Influence of nonuniformity of the ion background on the oscillation frequency of a virtual cathode

The oscillation frequency of a virtual cathode in a diode gap is investigated as a function of the density of the anode ion layer. It is shown that when the densities of the ion layer are high, a stable electron bunch forms in the flux, which leads to an increase in the oscillation frequency. Pis’ma Zh. Tekh. Fiz. 24, 74–80 (November 12, 1998)     

Enhanced emission during submillisecond low-energy electron beam generation in a diode with grid-stabilized plasma cathode and open anode plasma boundary

We have experimentally studied the phenomenon of emission enhancement in a gas-filled diode with grid-stabilized plasma cathode and open (mobile) anode plasma boundary at an accelerating voltage of up to 20 kV. As the working gas pressure is increased to p ≥ 10⁻² Pa and the longitudinal magnetic field is increased to B _z ≥ 20 mT, the current in the accelerating gap exhibits significant growth, sometimes by a factor of two or more. Experimental data show that the most probable mechanism responsible for this effect is ion-induced secondary electron emission from the emitting electrode surface bombarded by ions from plasma generated by the electron beam in the drift space. These ions are accelerated in the space charge layer between the emitting electrode surface and the mobile boundary of the beam-generated (anode) plasma.     

Formation of dense electron beams in a gun with a plasma anode based on a reflecting discharge

A method of obtaining low-energy, high-current electron beams in a gun with a plasma anode based on a reflecting discharge is proposed and implemented for the first time. Pis’ma Zh. Tekh. Fiz. 23, 42–46 (May 26, 1997)     

Structure of a picosecond electron beam inside a vacuum diode

The structure of a picosecond (∼150 ps) electron beam in the cathode-anode gap of a vacuum diode is determined. The electron beam is modeled in the form of flat quasiparticles with a definite charge density which follow one after another in equal time intervals. It is shown that the expansion of concentric layers of the beam under the action of the electric and magnetic self-fields strongly depends on the current strength. The experimental confirmation of the computed estimates is illustrated by recording the structure of the electron beam at the anode using a film which is sensitive to electron radiation. Pis’ma Zh. Tekh. Fiz. 25, 39–45 (September 26, 1999)     

Autocompensation of an ion beam in an accelerator with an anode sheath

Experiments to study the autocompensation of an ion beam are described. It is shown that in accelerators with an anode sheath and isolated collector, autocompensation occurs as a result of the excitation of an auxiliary non-self-sustained gas discharge. Pis’ma Zh. Tekh. Fiz. 23, 69–73 (May 26, 1997)     

Analytic model of the current-voltage characteristic of a small probe in a magnetic field

An analytic model is proposed for a small wall probe (whose dimensions perpendicular to the magnetic field are smaller than the ion Larmor radius) in a completely ionized plasma. The structure of the current collection regions is described and an analytic expression is obtained for the current-voltage characteristic of the probe. It is shown that a model with a classical diffusion coefficient gives results close to the experimental values. Pis’ma Zh. Tekh. Fiz. 24, 1–10 (November 26, 1998)     

Membrane oscillations in the channel of a steady-state plasma thruster

Extremely strong low-frequency oscillations (∼35 kHz) predicted earlier were observed experimentally in the channel of a steady-state plasma thruster. These oscillations are mainly caused by fluctuations of the electron temperature and affect the ion beam divergence. Pis’ma Zh. Tekh. Fiz. 25, 64–68 (June 12, 1999)     

Ion charge-state distribution in a high-power pulsed electron cyclotron resonance discharge sustained by millimeter-wavelength radiation

Measurements have been made of the ion charge-state distribution in a high-power, pulsed, electron-cyclotron discharge in argon sustained by millimeter radiation. It has been observed that the maximum of the distribution is shifted toward higher charge states compared with the distributions in conventional cw sources of multiply charged ions pumped by centimeter radiation. This shift of the distribution maximum evidently occurs because a so-called quasigasdynamic plasma confinement regime can be established in a magnetic trap when higher-power, shorter-wavelength gyrotron radiation is used, and in this regime, an increase in plasma density is accompanied by an increase in the confinement parameter Nτ, which determines the ion charge distribution. Pis’ma Zh. Tekh. Fiz. 23, 60–64 (April 26, 1997)     

The “zero” current and self-sustaining electron bunches in M-type devices

When the processes occurring in the entire interaction space of a magnetron device are included simultaneously in a numerical simulation it is possible to observe the onset and behavior of stable solitary electron bunches. It is shown that these self-sustaining electron bunches may be responsible for the existence of an anode current in the absence of rf interaction. Pis’ma Zh. Tekh. Fiz. 24, 57–62 (June 26, 1998)     

Plasma parameters of an electron cyclotron resonance discharge in a magnetic mirror in a quasi-gasdynamic confinement regime

An experimental investigation is made of x-ray bremsstrahlung in the 2–10 keV range of a pulsed discharge under electron cyclotron resonance conditions in a straight magnetic mirror system pumped by a high-power millimeter radiation beam. The plasma temperature and density were determined from the spectrum and intensity of the x-rays. The results indicate that a quasi-gasdynamic plasma confinement regime is achieved. Pis’ma Zh. Tekh. Fiz. 25, 90–93 (July 26, 1999)     

Scenario for the establishment of an electron beam “squeezed state” in a magnetically insulated vircator

A 2.5-dimensional particle-in-cell code was used to simulate different scenarios for the establishment of an electron beam “squeezed state” in a magnetically insulated vircator. Vircators with and without anode foils were compared. It was found that the squeezed state is established in both cases but the dynamics of establishment differ. Pis’ma Zh. Tekh. Fiz. 23, 29–33 (November 26, 1997)     

An electron source with a multiarc plasma emitter for obtaining submillisecond pulsed megawatt beams

An electron source with a plasma emitter based on an arc-discharge system with six cathodes and a common cylindrical hollow anode is described. Upon synchronous initiation of vacuum-arc discharges, the space of the hollow anode is filled by dense low-temperature plasma, the emission boundary of which is stabilized by a fine-structure metal grid with a 150-cm² area. The arc-current amplitude for each cathode amounts to 100–300 A. Under the action of a constant accelerating voltage applied between the plasma emitter and grounded accelerating electrode combined with the drift tube, electrons are extracted from plasma and accelerated. At a working pressure of 0.04 Pa, an electron beam with a maximum current amplitude of 1 kA has been obtained at an initial accelerating voltage of 80 kV and pulse duration (FWHM) of 100 μs, which has been transported in a longitudinal magnetic field of 0.035 T over a distance of 80 cm.     

Low-temperature nitriding of titanium in low-energy electron beam excited plasma

The effect of an electron beam and the related plasma on the structure, phase state, and microhardness of the surface of titanium has been studied in a broad range of beam currents (0.1–2.5 A), electron energies (0.1–1 keV), and gas pressures (0.01–1 Pa). This range was ensured by the grid stabilization of emissive properties of the plasma electron source, which formed a wide (∼40 cm²) electron beam in a space charge layer between the beam-excited plasma and the grid bounding the plasma cathode. The sample temperature (350–900°C) was determined by the electron beam parameters. The plasma density was additionally controlled by changing the gas (N₂ or Ar-N₂ mixture) pressure. It is established that, during the low-temperature nitriding process in low-energy electron beam plasma, the ion sputtering significantly affects the microhardness of a processed surface and the rate of growth of the hardened layer thickness. The possibility of nitriding at a low (−50 V) or floating potential of the sample eliminates the development of a surface relief and allows the process to be carried out in deep and narrow slits.     

A two-dimensional mathematical model of a short vacuum arc in external magnetic field: results of numerical calculations

The paper deals with the investigation of the impact made by two-dimensional effects on the process of passage of current in a short vacuum arc in an axial magnetic field. A two-fluid mathematical model is used, which is based on hydrodynamic and electrodynamic equations. The axial magnetic field B _z affects significantly the magnitude of two-dimensional effects: the two-dimensional effects increase with decreasing B _z . The simulation results demonstrate that the contraction of plasma density exceeds that of current density. The distribution of anode drop of potential on the anode surface is nonuniform; in the case of certain (critical) values of current, the anode drop goes to zero on the external boundary of plasma. The dependence of the critical current on B _z is determined. The distribution of current density on the starting plane is nonuniform with a maximum on the axis, and the ion trajectories are inclined to the discharge axis. The possibility is discussed of matching the solution in the plasma region of vacuum arc with that for cathode flames.     

Broadening of the particle resonance drift trajectory and tritium injection into a fusion reactor with an I=3 helical winding

Two fusion reactor problems, removal of helium ash and fuel (tritium) injection, can be solved using the concept of “drift island motion.” The motion of a drift island is an indicator of the broadening of the resonant trajectory of a charged particle guiding center. This trajectory broadening occurs if two conditions are satisfied. First, the drift pitch angle of the particle is equal to the resonance values i*=n/m, where n and m are the “wave numbers” of the perturbing magnetic field. Second, the drift pitch angle i*=n/m “moves” over the plasma cross section as the particle moves. This displacement is caused by a slow change in the helical magnetic field with time as the particle moves. It is shown that this effect may occur in a fusion reactor with an l=3 helical winding and may be used for tritium ion injection. Pis’ma Zh. Tekh. Fiz. 25, 5–13 (January 26, 1999)     

The Oktupol’ galathea electric-discharge confinement system

A new electric-discharge plasma confinement system based on an octupole magnetic field is described. The results of experiments with a confinement system using argon are reported. Pis’ma Zh. Tekh. Fiz. 25, 57–61 (September 12, 1999)     

阳极磁屏蔽霍尔离子源磁场的数值模拟

为了提高离子束电流和离子束能量,进一步增加霍尔离子源的效率,对霍尔离子源阳极进行磁屏蔽,达到优化磁场位形,增强磁场对放电等离子体的约束。由磁场的数值模拟结果可知:阳极磁屏蔽后,有明显凸向阳极表面的弯曲磁场线,并且提高了磁镜磁场的磁镜比;大的正梯度磁场的存在,增强了磁场的径向分量,相对减弱了放电等离子体的震荡;不仅保留原有鞍形场的作用,而且还充分发挥了另外两个鞍形场的优势。最后通过实验结果和数值模拟结果的比较,验证了此数值模拟结果的正确性。