A planar diode operating in the regime of limited electron emission

The current-voltage characteristic of a planar diode with a graphite explosive-emission cathode has been experimentally studied at the initial stage of electron current formation. An analytical expression has been obtained for the total area of discrete emitting centers in the cellular structure approximation, assuming that the number of such emitting centers operative during the current pulse formation is constant. It is shown that the electron current buildup for a cathode surface with discrete emitting centers is satisfactorily described by a modified Child-Langmuir formula with the form factor decreasing from F = 6 to 1.     

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)     

Phase evolution and electron bunching in two frequency undulator

A two frequency undulator is considered as a medium for interaction between an electron beam and two transversal electromagnetic waves. A one dimensional approach in small signal gain regime is employed and a set of linear equations governing the energy and phase evolution of the system is derived and is studied numerically. The bunching factor for two sort of bunching process, corresponding to two independent components of the undulator, is investigated.     

Low-loss electron beam transport in a high-power, electrostatic free-electron maser

At the FOM Institute for Plasma Physics “Rijnhuizen”, The Netherlands, the commissioning of a high-power, electrostatic free-electron maser is in progress. The design target is the generation of 1 MW microwave power in the frequency range 130–260 GHz. The foreseen application of this kind of device is as a power source for electron cyclotron applications on magnetically confined plasmas.

The device is driven by a high-power electron beam. For long-pulse operation a low loss current is essential. A 3-A electron beam has been accelerated to energies ranging from 1.35 to 1.7 MeV and transported through the undulator at current losses below 0.02%. Further, it was shown that the beam line accepts an electron energy variation of 5% with fixed beam optics. This is essential for rapid tuning of the microwave frequency, over 10%.

Electron beam simulations have shown to be remarkably accurate both for the prediction of the lens settings and for the intercepted current. The operational settings of the beam line which give the highest current transmission are within a few percent of the simulated values.     

Differential impedance of solid-state supercapacitor operating in a hybrid regime

The behavior of the differential impedance of a solid-state supercapacitor in the course of a charge/discharge cycle in the region of potentials including a hybrid regime has been studied. Both real and imaginary parts of the impedance exhibit a hysteresis. A large number of features observed on the experimental curves indicate that the energy accumulation process has a much more complicated character than that stipulated by the existing model.     

Electrode self-cleaning in a barrier ozonizer operating in a turbulent gas flow regime

The effect of self-cleaning of the discharge gaps in electric barrier ozonizers featuring a turbulent gas flow is related to the fact that the hydrodynamic forces (separating foreign solid and liquid particles from the electrode surface) predominate over electric forcers (attracting such particles to the electrodes). In this respect, ozonizers operating in a turbulent gas flow regime are advantageous over devices operating with a laminar flow.     

Cyclotron resonance of electrons and holes in graphene monolayers

We report studies of cyclotron resonance in monolayer graphene. Cyclotron resonances are detected by observing changes in the photoconductive response of the sample. An electron velocity at the Dirac point of 1.093 x 10(6) m s(-1) is obtained, which is the fastest velocity recorded for all known carbon materials. In addition, a significant asymmetry exists between band structure for electrons and holes, which gives rise to a 5% difference between the velocities at energies of 125 meV away from the Dirac point.     

Amplitude-frequency characteristic of a nonlinear spin wave interferometer operating in a quasi-nonlinear regime

A thin-film nonlinear spin wave interferometer has been experimentally studied. The concept of a quasi-nonlinear operation regime is introduced for the first time and the boundaries of the quasi-nonlinear dynamic range of the interferometer are experimentally determined. It is shown that the nonlinear spin wave interferometer operating in the quasi-nonlinear regime can be characterized, like linear devices, by the amplitude-frequency characteristic (AFC). However, an increase in the signal power level within the quasi-nonlinear dynamic range at the input of the nonlinear interferometer leads, in contrast to the case of a linear device, to a frequency shift of the AFC. An analysis of the AFC shift indicates that a 180° change in the phase difference between the interfering signals at each separate frequency is achieved for the input power varied within the limits of the quasi-nonlinear dynamic range. This behavior shows the possibility of using the nonlinear interferometer for the processing of microwave signals without undesired distortion of the signal waveform.     

Experimental investigation of graphite explosive-emission cathodes operating in a periodic pulse regime

We have studied the electron emission from graphite cathodes under the action of voltage pulses with an amplitude of up to 300 kV, a pulse duration of 10^?9 s, and a pulse repetition frequency of 1–3.5 kHz. The magnetically insulated electron beam had a peak power of up to 600 MW at an average power of 1–3 kW. The dynamics of emission current delay was studied in relation to the charge transferred by the beam and to the state of the cathode surface (studied by scanning electron microscopy). It is established that smoothening of the microrelief leads to degradation of the cathode emissivity, which can be compensated by increasing the pulse repetition rate above a certain critical level.     

High-power free-electron maser with frequency multiplication operating in a shortwave part of the millimeter wave range

The possibility of using frequency multiplication in order to obtain high-power short-wavelength radiation from a free-electron maser (FEM) with a Bragg resonator has been studied. Preliminary experiments with an LIU-3000 (JINR) linear induction accelerator demonstrate the operation of a frequency-multiplying FEM at megawatt power in the 6- and 4-mm wave bands on the second and third harmonic, respectively.     

Suppressing electron bunching at low harmonics in gyromultipliers of the klystron type

We propose a method of selective suppression of the electron bunching at low harmonics of the external drive frequency in gyromultipliers of the klystron type. This approach improves the selectivity of generation at the multiple frequency by decreasing the probability of parasitic low harmonic excitation of the output cavity. The analytical conclusions are confirmed by the results of numerical simulation of the electron bunching space in a weakly relativistic gyromultiplier.     

The effective anode-cathode gap in an ion diode operating in a bipolar-pulse regime

The effective anode-cathode gap (ACG) in a self-magnetically insulated ion diode operating in a double (bipolar) pulse regime has been studied. In this diode, the ACG is bounded by a plasma layer at the anode surface and by electrons drifting near the cathode surface. Analysis of the system operation showed that, during the first voltage pulse, the effective ACG decreases at a constant velocity of 1.5 ± 0.1 cm/μs from 9 to 1–2 mm (depending on the pulse duration) and is not completely bridged by plasma. After reversal of the voltage polarity, the effective gap width is restored for 10–20 ns on a nearly initial level. During the second pulse, electrons drift within a 1- to 1.5-mm-thick layer near the anode, while the thickness of a plasma layer on the anode surface does not exceed 0.5 mm.     

Possibility of using a large orbit regime for operation at bounce-frequency harmonics in a free-electron maser with a guiding magnetic field

It is suggested that a free-electron maser based on the LIU-3000 accelerator (Joint Institute for Nuclear Research, Dubna) can be made to emit in the short-wavelength part of the microwave range by using radiation at harmonics of the bounce frequency of an electron beam propagating along a helical trajectory with a large gyration radius on the transverse inhomogeneity scale of the rf field and selectively exciting a cylindrical waveguide mode whose azimuthal index is equal to the number of the harmonic. Pis’ma Zh. Tekh. Fiz. 25, 30–36 (January 12, 1999)     

Design and construction of a table top microwave free electron maser for industrial applications

This paper reports the development of a reasonably low-cost free electron maser (FEM) as a source of tuneable, focused microwave power for industrial applications. In this paper the principle of operation and general system set-up will be presented. To date the FEM is operating at a power level that has allowed us to perform experiments with low-pressure plasmas in UV lamps.     

Nanometer vibrations measured using a semiconductor laser on quantum-confined structures operating in an autodyne regime

A method for the quantitative monitoring of nanometer vibrations has been developed based on the autodyne detection effect in a semiconductor laser. It is shown that the semiconductor laser autodyne can be used for measuring the amplitudes of vibrations in a range from one nanometer to 10 μm in a frequency band from a few hertz to several hundred megahertz. With the aid of a lock-in amplifier, the lower threshold of measured vibration amplitudes has been reduced to one ångström.     

An electrical probe with electron emission in the regime of a continuous medium

The influence of electron emission on the current-voltage characteristics of a cylindrical probe placed in a weakly ionized, dense plasma with constant properties and frozen-in chemical reactions is considered.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 52, No. 2, pp. 224–227, February, 1987.     

A model of electron emission from a wedge in the space-charge-limited current regime

The process of electron emission from a wedge-shaped cathode in the space-charge-limited current regime has been theoretically studied. The field distribution in the interelectrode gap is described using a simple analytical model, which is based on the matching of self-similar solutions for electron flows at the vertex region and at the periphery. The dependence of the perveance on the wedge angle in the wedge cathode-flat anode system is determined.     

Conduction electron spin resonance in gold

Conduction electron spin resonance has been observed in transmission through pure gold slabs of 100, 260, and 490 µm thickness covered on each side by a thin ferromagnetic film. This resonance corresponds tog=2.11±0.01 and broadens rapidly above 10 K, in agreement with spin orbit relaxation by phonons.Laboratoire associé au CNRS.