The operation of hollow anodes (HAs) with either multi-arc or magnetron-like or ferroelectric plasma source (FPS) ignition is described. These HA sources produce in the vicinity of the HA output grid a plasma with a density n approximate to 5 X 10(12) cm(-3) and this plasma acquires a positive potential of several tens of volts. HAs with an incorporated FPS have demonstrated the best operation characteristics and smallest dimensions. Also, the FPS allows us to achieve an HA discharge with a current amplitude I-d less than or equal to 1.2 kA at a gas pressure of about 10(-5) Tom These HA modifications were used as a cathode in a diode powered by a 200 W, 400 ns pulse. The parameters of the electron beam with an amplitude of 1.5 kA or less are presented. The accelerating pulse causes an increase in the HA plasma potential of up to 6kV. A model that explains the electron emission from the positively charged plasma is proposed.

We review the operation of a ferroelectric plasma source (FPS) with enhanced plasma density and of high-current hollow cathode (HC) and hollow anode (HA) discharges. Different schemes (arc sources, magnetron and FPS) were used for ignition and sustaining the HC and HA discharges with current amplitude ⩽4kA.These discharges are characterized by a positive anode potential with respect to the hollow electrode walls and the plasma density and temperature inside the hollow electrode cavity reach ∼3×1019m−3 and ⩽12eV, respectively. It was shown that the incorporation of the FPS in the HA and HC enables one to develop a compact high-current electron source. The characteristics of an electron diode with FPS, HA and HC were studied under an accelerating voltage ⩽250kV and ∼400ns pulse duration. It was shown that these sources allow the generation of an electron beam with a cross-sectional area of 0.01m2 and amplitude up to 1–2kA.

An investigation of the properties of the plasma and the electron beam produced by velvet cathodes in a diode powered by a ∼200kV, ∼300ns pulse is presented. Spectroscopic measurements demonstrated that the source of the electrons is surface plasma with electron density and temperature of ∼4×1014cm−3 and ∼7eV, respectively, for an electron current density of ∼50A∕cm2. At the beginning of the accelerating pulse, the plasma expands at a velocity of ∼106cm∕s towards the anode for a few millimeters, where its stoppage occurs. It was shown by optical and x-ray diagnostics that in spite of the individual character and nonuniform cross-sectional distribution of the cathode plasma sources, the uniformity of the extracted electron beam is satisfactory. A mechanism controlling the electron current-density cross-sectional uniformity is suggested. This mechanism is based on a fast radial plasma expansion towards the center due to a magnetic-field radial gradient. Finally, it was shown that the interaction of the electron beam with the stainless-steel anode does not lead to the formation of an anode plasma.

The operation features and the main physical parameters of different modifications of hollow anode (HA) plasma sources based either on multi-arc, or on magnetron-like, or on ferroelectric plasma source (FPS) ignition are described. It was found that these HA sources produce in the vicinity of the HA output grid a satisfactory unifonn plasma with a density n≈ 5×1012 cm-3. It was found that during the HA discharge the plasma acquires a positive potential of several te ns Volts. The HA with incorporated FPS demonstrated the best operation characteristics. It was found that the FPS allows reliable ignition and sustaining of the HA discharge with current amplitude Id≤1.2 kA and pulse duration ≤2×10-3 s at N2 gas pressure of ~ 10-5 Torr. During the HA discharge the density of the FPS surface plasma was found to be 8×1014 cm-3 that allows one to consider FPS as a practically unlimited electron source. In addition, the FPS allows one to decrease signiticantly the overall HA dimensions, thus providing a very compact design. All three HA modifications were used as a cathode in a diode powered by a 200 kV, 400 ns pulse. The parameters of the generated electron beam with an amplitude ≤1.5 kA and the diode characteristics are presented. It was found that the applied accelerating pulse causes a significant up to 6 kV increase of the plasma potential (φpl) inside the HA. A model that explains the electron emission from the positively charged plasma is proposed.

Spectroscopic measurements are reported of the plasma formed inside a hollow anode (HA) with a ferroelectric plasma source (FPS) incorporated in it. The HA was used as a cathode in a diode supplied by an accelerating pulse (≤300kV, ≤400ns). It was found that the HA discharge (1.2kA, 10μs) is accompanied by the formation of a dense (≈8×1014cm−3) plasma layer at the surface of the FPS. This surface plasma serves as a practically unlimited source of electrons. In the bulk of the HA plasma the density is ≈3×1013cm−3 and it remains the same during the accelerating pulse whereas the plasma electron temperature increases from 4 to 11eV.

We present results which show drastic changes in the parameters of a hollow anode (HA) which serves as a cathode in an electron diode. The HA has a ferroelectric plasma source (FPS) incorporated in it. The applied accelerating pulse causes increase of the potential of the plasma inside the HA up to 7 kV and switches the direction of the current of plasma electrons from the HA and its output grid towards the accelerating gap. It is shown that, in spite of the large positive plasma potential, electron emission occurs due to the dynamics of ion motion in the sheath near the HA grid.

We describe the operation of a hollow-anode electron source with a biased output grid in a diode powered by a 200 kV 400 ns pulse. The hollow anode had a ferroelectric plasma source incorporated in it. Three electrical schemes for the hollow-anode output grid bias were tested and compared. It is shown that the use of an autobias grid allows electron-beam generation with a current amplitude up to 1.2 kA in a plasma emission-limited mode and with insignificant plasma prefilling of the accelerating gap. The use of an externally biased output grid (either with a positive or negative potential) showed the possibility to control the emission properties of the hollow-anode plasma without changing the amplitude of the discharge current. Electron beams with an amplitude up to 2 kA and insignificant plasma prefilling of the accelerating gap were obtained. It was found that the application of the accelerating pulse leads to a drastic increase in the potential of the plasma up to several kV. It is shown that, in spite of the large positive plasma potential, electron emission occurs due to the dynamics of ions inside the sheath near the hollow-anode grid.

We describe the operation of a hollow plasma anode (HPA) with a hollow cathode incorporated in it for the production of preliminary plasma. The operation of the hollow anode was studied with a discharge current amplitude up to 1 kA. It was shown that the gaseous discharge is realized without formation of plasma spots at the anode wall and the output grid. The plasma parameters inside the HPA were measured for different N2 gas pressures and discharge current amplitudes. It was found that the plasma acquires a positive potential with respect to the anode and that the plasma density and temperature are ⩽5×1012 cm−3 and ⩽10 eV, respectively. This plasma source was used as a cathode in a diode for the generation of high-current electron beams under an accelerating-voltage ⩽250 kV and 400 ns pulse duration. The characteristics of the diode and the generated electron beam as a function of the HPA parameters are presented. It was found that at the beginning of the accelerating pulse the diode operates in a plasma prefilled mode, and further in the accelerating pulse the diode current is determined by the emission capability of the HPA. It was shown that this source allows reliable generation of a uniform electron beam with a cross-sectional area of 100 cm2 and a current amplitude up to 1 kA without the formation of explosive plasma at the HPA output grid.

Summary form only given. Over the past decade intensive research in many laboratories was focused on the investigation of strong electron emission from ferroelectric samples. It was demonstrated that ferroelectric samples could emit electron current densities of hundreds of A/cm/sup 2/ with a repetition rate of several of MHz under the application of driving pulses with an amplitude of /spl sim/10/sup 3/ V. Two models were suggested to explain the observed electron emission. The first model is based on polarization reversal of the prepolarized ferroelectric sample which causes the appearance of noncompensated polarization charge and, consequently, large electric field on the surface of the ferroelectric. The second model suggests electron emission from the plasma which is created on the surface of the ferroelectric due to incomplete surface discharge. We present data which show the validity of the second model, namely that the source of electrons is the plasma. This plasma is formed by incomplete discharges on the surface of the ferroelectric sample within the first few nanoseconds of the driving pulse application. The parameters of the surface discharge plasma (plasma electron density and temperature, plasma expansion velocity, energy of plasma electrons and ions, and plasma uniformity) as well as the parameters of the neutral flow strongly depend on the polarization state of the ferroelectric material as well as on the parameters, and method of application of the driving pulse application. Data concerning the life-time of ferroelectric cathodes versus the driving pulse parameters are presented as well. We also describe the parameters of the electron beams generated in planar electron diodes with ferroelectric cathodes. It is shown that electron beam generation in a diode with a ferroelectric cathode is realized in the so-called plasma prefilled mode. Data are also presented concerning the uniformity of the extracted electron beam as well as the potential distribution in the diode.

We report experimental results of operation of a high-current hollow anode (HA) with a BaTi ferroelectric plasma source (FPS) incorporated in it. It is shown that the application of the FPS allows one to significantly decrease the HA surface area, thus providing a compact electron source. Use of this HA as an electron source in a high-voltage diode for generation of high-current electron beams is described as well. It was found that the FPS allows reliable ignition and sustaining of the HA discharge with current amplitude ⩽1.2 kA and pulse duration ⩽2×10−5 s at N2 gas pressure of (1–3)×10−4 Torr. Also, it was found that the operation of the HA is characterized by plasma formation with density of ∼4×1012 cm−3, electron temperature of ∼5 eV, and that the plasma acquires a positive potential of ∼10 V with respect to the anode and of 50–70 V with respect to the autobiased HA output grid. It is shown that the autobiased HA output grid prevents plasma penetration towards the accelerating gap if the grid half-cell size has approximately the same value as the thickness of the double layer formed between the plasma and the grid wires. Generation and characterization of a high-current electron beam with current amplitude of ∼1.2 kA was achieved under an accelerating pulse amplitude ⩽300 kV and ∼400 ns pulse duration.

We present experimental results of electron beam generation in a diode with cathodes made of BaTi solid solution and prepoled and unpoled PZT ferroelectrics without a screening grid in front of them. The diode operates with an accelerating pulse of ∼200 kV and ∼300 ns duration. It was found that although a surface plasma is always formed as a result of the application of a driving pulse, the beginning of the electron emission does not always coincide with the start of the accelerating pulse. Namely, it was shown that the application of the accelerating pulse at the same time with the driving pulse leads to simultaneous electron emission from the surface plasma only in the case of coincidence of the driving and accelerating electric field directions. In the opposite case, electron emission starts only at the end or at the fall of the driving pulse for the BaTi and PZT samples, respectively. Also, it was found that the electron beam current density distribution corresponds to the plasma emission spots which appear at the ferroelectric surface.

We report on the operation of an electron diode with a cathode based on a hollow plasma anode (HPA) design. Six arc sources placed inside the anode cavity were used to produce a preliminary plasma. The latter was used to produce a high-current (up to 4 kA) gaseous discharge without formation of plasma spots at the anode wall and output grid. The plasma parameters inside the HPA were measured for different N2 and Xe gas pressures and discharge current amplitudes. It was found that the HPA operation is characterized by a negative anode potential fall and that the plasma density and temperature inside the anode are ≈6×1012 cm−3 and ≈9 eV, respectively. The characteristics of an electron diode and the generated electron beam were studied under an accelerating voltage amplitude ⩽250 kV and 400 ns pulse duration for different parameters of the HPA. It was found that in the beginning of the accelerating pulse the diode operates in a plasma prefilled mode while later the diode current is determined by the emission capability of the HPA plasma. It was shown that this source allows generation of an electron beam with a cross-sectional area of 100 cm2 and a current amplitude up to 1.2 kA, without the formation of explosive plasma at the surface of the HPA output grid.

This paper presents results and analysis of an experimental investigation of the operation of a hollow cathode (HC) with an incorporated ferroelectric plasma source (FPS). It was shown that the use of FPS based on a BaTi solid solution allows one to ignite and to sustain a 102-103 A HC discharge with duration of 10-3-10-5 s at background pressure of \(\sim\) 5 x 10-3 Pa while keeping the HC design with small dimensions. It was found that the development of the HC discharge is accompanied by formation at the surface of the FPS of dense plasma which serves as a powerful (hundreds of kW) pulsed source of current carrying electrons. Parameters of the HC plasma (radial distribution of the plasma density and temperature and plasma potential) for different discharge current amplitudes and two types of FPS are presented. Application of the FPS as an electron source in a diode under an accelerating pulse \(\leq\)300 kV and pulse duration \(\leq\)400 ns showed that the latter operates in a plasma pre-filled mode with a current amplitude up to 1.6 kA. Parameters of the diode and electron beam for different experimental conditions are presented and discussed.

In this paper the parameters of two types of high-current switches based on ferroelectric BaTiO3 ignition are presented. Both types of switches showed a reliable and controllable operation with a repetition rate of several Hz. The first type is a vacuum two-electrode switch ignited by the plasma which is generated by a BaTiCO3 cathode. This type of switch was tested in the voltage range of 3–25 kV and switched current amplitude of 2 –15 kA with either negative or positive polarity of the high-voltage electrode. The second type is a BaTi03 surface flashover strip-like switch ignited by a driving pulse which has an amplitude of several kV. It was shown that the application of the driving pulse (>10 kV) leads to the appearance of many non-complete surface discharges which transform further to a multi-channel discharge. This type of switch was tested in the voltage range of 1–25 kV and current amplitude of 0.5–15 kA. The design of the switches, their lifetime, the time jitter and the parameters of the switched current for different discharge conditions are presented.

We report the parameters of a hollow cathode with a ferroelectric plasma source incorporated in it. It was found that this source allows the ignition and sustaining of a high-current discharge (⩽1.4 kA, ⩽2×10−5 s) at N2 gas pressure of (3–5)×10−4 Torr. It was shown that ∼85% of the discharge current is emitted by the ferroelectric sample. The plasma in the cathode acquires a positive potential (⩽50 eV) with respect to the anode and the plasma density and temperature are ⩽8×1012 cm−3 and ⩽18 eV, respectively. Generation of an electron beam (0.3–1.6 kA, 300 ns) was demonstrated under an accelerating pulse ⩽300 kV.

In this paper the parameters of a hollow-cathode electron source and generated electron beam are presented. A gas-puff valve is used to provide a sharp pressure gradient between the cathode cavity and the accelerating gap. Parameters of a He gas and the plasma inside the cathode and the accelerating gap studied by electrical and optical diagnostics for different gas pressure and an amplitude of the discharge current are presented. It was found that the operation of the HC is characterized by a negative anode potential fall and that the plasma density and temperature do not exceed 5/spl times/10/sup 12/ cm/sup -3/ and 14 eV, respectively. Parameters of the electron beam for different discharge current and anode grid cell sizes are presented. It was shown that efficient electron beam generation with an amplitude of the beam current up to 300 A does not lead to significant increase of the plasma potential. The results of the simulation of the HC operation agree with the obtained data.

We present results of the investigation of different types of cathodes operating in an electron diode powered by a high-voltage generator (300 kV, 250 ns, 84 Ω, ⩽5 Hz). The cathodes which have the same emitting area of 100 cm2 are made of metal–ceramic, carbon fibers, carbon fabric, velvet, or corduroy. We also tested carbon fibers and carbon fabric cathodes coated by CsI. It was shown that for all types of cathodes the electron emission occurs from the plasma which is formed as a result of a flashover of separate emitting centers. The amount of the emitting centers and the time delay in the electron emission were found to depend strongly on the accelerating electric field growth rate. Experimental data concerning the uniformity of the light emission from the cathode surface and divergence of the generated electron beams are presented. Data related to the general parameters of the diode, namely its impedance, power, and energy are given as well. For all the cathodes investigated the observed diode impedance indicated the existence of a quasistationary cathode plasma boundary for electron current density ⩽20 A/cm2. We present the dependencies of the average emitted electron current density and of the time delay in the electron emission on the number of generator shots. We also present data of the vacuum deterioration as a result of the tested cathodes operation. The obtained data are discussed within the framework of plasma formation as a result of cathode surface flashover.

We present results of studies of emission properties of cathodes at accelerating fields of 3 – 6×104 V/cm. We investigated cathodes which are made of metal-ceramic, carbon fibers, carbon fabric, velvet or corduroy. Experimental data concerning light emission from the cathode surface, uniformity and divergence of the generated electron beams are presented. Data related to the impedance, power, and energy of diodes operating with these cathodes are given as well. It was found that the tested cathodes, except the cathode made of carbon fibers, showed significant degradation of their emission properties within 4×103 generator shots. We also present data of the vacuum deterioration as a result of cathode operation.