of operating both in negative and positive polarities, and the number of pulse forming lines feeding the inductively isolated cavities was reduced to half. These modifications were recently tested in positive polarity. An increase in the total accelerating voltage from 5.5 MV to 9 MV was observed while stressing all components to the level required to achieve 12 MV in negative polarity. In these experiments only 65% of the usual operating intermediate store capacitor voltage was necessary (1.7 MV instead of 2.6 MV). Currently, the device is reconfigured for negative polarity tests. The cavities are rotated by 180{degree} and a 17-inch spool is added at the base of the cantilevered center electrode (cathode electrode). Positive and negative polarity results are presented and compared with simulations.
In the presented experiments the Thomson scattering technique, based on the second harmonic of Nd-glass laser was used for studying of a non-Maxwellian electron distribution function of the plasma, heated by REB. Two simultaneously operating systems were employed for observation of light scattered at the angles of 90 and 8 degrees, respectively. The first obtained results and the mechanisms of plasma heating are discussed.
The influence of high power pulsed ion beam irradiation and final heat treatment on physical and chemical state of refractory alloys (VT25U, VT9, GS26) blades surface layers were investigated after their operation in gas turbine engine. It is shown that ion beam treatment allows to reconstruct and recovery service properties of these parts.
First experimental results on microwave radiation at double plasma frequency from plasma heated by similar to 100 keV, 2-10 MW electron beam of similar to 100 mu s duration in GOL-3 are presented. Measurements were done in 75-200 GHz band. The spectrum was peaked at similar to 94 GHz at similar to 3.10(13) cm(-3) plasma density, the temporal behavior of radiated power was spiky. The generation efficiency reached similar to 1% of total beam power.
Bremsstrahlung X-rays produced at the collector can be used for definition of electron energy distributions in gyrotrons and maybe in other high-power microwave devices. Such a possibility underwent early testing at the Karlsruhe Institute of Technology on two gyrotrons. Electron energy distributions calculated on the basis of X-ray spectra measured near the gyrotrons operated at different regimes have plausible shapes and demonstrate good correlation with expected characteristics of the electron beam, thus confirming the viability of the proposed diagnostic technique.
The generalized model is suggested for the physical processes while the convert ion of the field emission into explosive emission of electrons, accompanied by abrupt destruction of the emitter and the intensive dispersion of its material. The complex of the phenomena is considered, allowing for nonstationarity and spatial inhomogeneity of the correlated electromagnetic, thermal and gasdynamic processes, as well as the peculiarities of the thermal properties of the substances arising under considered conditions. Numerical analysis of the electric explosional processes is carried out and the discussion of the obtained results is accomplished.
We have studied confinement of hydrogen ions in a mirror field to estimate the feasibility of beam confinement fusion. A molecular-hydrogen beam of about 20 keV was injected in the mirror field to confine the dissociated hydrogen ions. In this MIGMA-like experiment, the number density of the ions was about 1011 m−3 in a central region. A relaxation time of the confinement was measured by means of neutral-particle detection. The present energy range of 20 ke V results in the shortest relaxation time because of the largest cross section of the charge exchange process. The observed relaxation time of about 1 ms was governed by collision with residual hydrogen gas. We have also performed a computer simulation to estimate the highest ion density obtainable for a case of the 3HeD fusion. The behaviour of the ions and the associated electrons was calculated by means of particle-in-cell code. For this calculation, we assumed injection of high-energy intense pulsed 3He beam into a background plasma of D2. The confinement properties were examined as a function of the background plasma density.
A gyrotron traveling wave amplifier (gyro-TWA) with a cusp electron gun and a helically corrugated waveguide operating in the W-band is presented. The large orbit electron beam from the cusp gun interacts resonantly with an ideal eigenwave existing in the interaction region based on the cyclotron resonance maser instability. When driven by the electron beam of energy 40 keV and current 1.5 A, the amplifier was simulated to output 10 kW (CW) with a 3 dB frequency bandwidth of 90-100 GHz and saturated gain of 40 dB. Linear analysis and numerical simulations of the performance characteristics of the amplifier will be presented.
Optimization for L-band ladder cathode MILO based on an existing model is carried out. The efficiency is improved by changing the parameters of choke and SWS vanes. The resonant frequency and Q factor are obtained through numerical calculation of open cavity high frequency characteristics. Then a 2.5-dimensional electromagnetic PIC code is used for optimizing simulation. Employing an electron beam of 568 kV, 53.3 kA, a TEM mode high power microwave with output power of 5.5 GW, frequency of 1.2 GHz is obtained. The power conversion efficiency is 18.2%.
This paper presents a Monte-Carlo model to investigate the single-surface multipactor discharge and its high-power absorption on a dielectric surface in the presence of the RF and dc electric fields. By employing a novel method in the numerical implementation of the secondary electron emission, the susceptibility diagram is constructed; beam loading and its power absorption by the multipactor discharge are examined; meanwhile the temporal evolution of the multipactor is also studied. The simulation results show clearly that (1) a steady state multipactor can be built up from a very low density initial electron distribution and an oscillatory steady state can be achieved when the positive charge, left by the emission of secondary electrons, is capable to build a large enough dc electric field; (2) during the saturation state, the normal electric field and the number of electrons in flight oscillate at twice the RF; (3) the average power absorbed by the multipactor, strongly depending on material parameters, is on the order of 1% incident power or less. Based on these results, the mechanism of RF window breakdown under high-power microwave conditions is suggested and several useful guidelines to prevent or extinguish the multipactor are presented.
Intense pulsed heavy ion beam is expected to be applied to materials processing including surface modification and ion implantation. For those applications, it is very important to generate high-purity ion beams with various ion species. A magnetically insulated ion diode with an active ion source of a vacuum arc plasma gun has been developed in order to generate pulsed metallic ion beams. When the ion diode was operated at diode voltage ≈200 kV, diode current ≈15 kA and pulse duration ≈100 ns, the ion beam with an ion current density of >; 200 A/cm2 was obtained at 50 mm downstream from the anode. From Thomson parabola spectrometer measurement, the ion beam consists of aluminum ions (Al+, Al2+ and Al3+) of energy 60-300 keV and the proton impurities of energy 60-150 keV. The purity of the beam was estimated to be 89%.
