High-power Electron Beam Research Articles

The multiplet cavity: A buncher for broad-bandwidth klystron amplifiers

The bandwidth of a klystron output cavity scales (approximately) as p/sup 0.8/P/sup 0.2/, where p is the beam perveance and P is the beam power. For high-perveance (p>10 /spl mu/pervs) high-power (P>10 kW) electron beams, it is relatively straightforward to design a broad-band output cavity. However, the design of the input cavity of the broad-band klystron is in some ways more difficult. The purpose of the input cavity is to produce a velocity-modulated electron beam with a frequency-dependent modulation amplitude that will optimize the bandwidth of the entire klystron system, while providing a magnitude of velocity modulation large enough to minimize the length of the klystron. This paper shows how a multiplet (multiple cavity) buncher cavity can be designed to provide broad-band (>20%) operation while keeping short the drift section length of the klystron.

Desktop repetitive sources of powerful electron beams, X-ray and microwaves for lab investigations in radiation chemistry, physics and biology

We present results of the research and development work that has made it possible to create compact repetitive sources of high-power electron beams, X-rays, and microwaves. Laboratory investigations require that specific parameters of the e-beam, X-rays, and microwaves be high. It is energetically more advantageous to increase average power by using repetitive devices. The basic unit of such devices represents a RADAN303B high-voltage driver, which permits one to generate 4 ns accelerating voltage pulses energizing vacuum diodes (direct-action accelerating tubes) based on cold explosive-emission cathodes.

Technical status of the first industrial unit of the 10 MeV, 100 kW Rhodotron

The Rhodotron is a new type of industrial electron accelerator developed by IBA, Belgium, on the basis of the pioneering work performed by a French team at CEA, Saclay. The operating principle of this new technology makes it possible to easily produce high energy and high power electron beams. The combination of high energy and high current allows high product throughputs and/or the irradiation of thick structures in the electron mode. An X-ray target is also developed in such a way that the Rhodotron can also be operated in the X-ray mode while maintaining high dose rates. The construction of the first industrial unit (10 MeV, 100 kW) began in January 1992 and the first beam was obtained on October 29, 1993. This machine has now been tested at its full specifications. Technical performance data are presented in this paper.

A Tracking Problem Solved with Fuzzy and Neural Control in Electron Beam Technologie

The accuracy in the control of beam position is high in tracking operation. The control parameter on older version depends on ‘visual’ observation of an image or in ‘manual’ introduction of trajectory co-ordinates. This paper is based on experiments made on a high power electron beam processing system used in special welding technologies. This paper presents an improvement of this system using captured images to extract welding parameters from it (tracking based on visual information). A captured image with 256×256 pixels (1 byte per pixel 256 grey level) provides information this type of control process. Using control methods, it is possible to handle very special shapes on the surface of a material or contact lines of two different materials with random contact contour.

Physics of electron emission from metal-dielectric cathodes

The present paper gives a description of the metal-dielectric cathode interaction. There is an explosive electron emission on the cathodes, that occurs through explosions of the metal microprotrusions at so-called triple points (metal-dielectric vacuum). The current of a vacuum discharge over the dielectric surface plays an initiating role. Such a mechanism of emission operates in low-voltage ferroelectric cathodes, in cathodes of long service in high-power pulse repetitive accelerators, as well as in the cathodes used in focusing high power electron beams.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance of boron containing materials under disruption simulations and tokamak divertor plasma testing

The behavior of thick B 4C coatings on different graphites under high power electron beam irradiation, pulsed plasma irradiation and under DIII-D divertor plasma action was investigated. SiCB 4C coating on graphites produces in General Atomics and pyrolytic boron nitride were also tested in the plasma gun device. In the following tests at these facilities, the samples were examined using SIMS, EDAX, X-ray crystallography, profilometry and Auger spectroscopy. B 4C coatings showed excellent durability under high heat flux irradiation and in conditions of real tokamak divertor plasma. The obtained results indicated that the use of RGT graphite (the graphite with high thermal conductivity) improves the durability of the B 4C coating significantly. Pyrolytic boron nitride showed very small removal of the matter and no mechanical damage.

95/00323 Hydrogen production from coal conversion under high-power electron beams

95/00323 Hydrogen production from coal conversion under high-power electron beams

Hydrogen production from coal conversion under high-power electron beams

A large-scale study of coal gasification by steam and coal cooking processes under an electron beam with a power of up to 80 kW has been carried out. The product formation rates, energy consumption and energy storage in products were determined. The energy efficiencies of the processes were estimated. Some energy problems and a comparison with traditional methods of coal conversion have been considered.

Improvement of electron beam shape control in radiation processing

The development of radiation processing using electron accelerators requires good control of the treatment parameters to improve the dosimetry quality. Especially, the analysis of the shape of the scanned electron beam that interacts with the product, is of prime necessity. A Multiwire Beam Shape Analyser (MBSA) has been developed by the AERIAL Laboratory in order to insure good monitoring of the scanning length and uniformity. This device consists of an aluminum beam-stop covered with a mesh of individually insulated stainless steel wires, placed under the scanning cone. The current generated by the impact of the electron beam on each wire is converted into voltage. After pulse shaping and multiplexing of the different channels, the beam profile can be displayed on an oscilloscope or on a PC screen. A prototype is now operating on an experimental irradiation plant based on a 2.5 MeV /300 W Van de Graaff electron accelerator. It allows almost continuous visualization of the beam profile (between two conveyor passes) and its response was compared to classical film dosimeters (Gafchromic, FWT 60.00). Considering FWHM and homogeneous treatment regions of the profiles, MBSA and the dosimeters give similar responses and variations remain lower than ± 12%. The acquisition of an electrical signal corresponding to the beam profile in air constitutes the original aspect of the MBSA and is in keeping with the general pattern of continuous control and automation of the irradiation processes. Hereafter, much work has to be done to adapt this device to an industrial use (higher energy, high power electron beams, non-destructive measurements…).

Efficiency enhancement of high power vacuum BWO's using nonuniform slow wave structures

The Sinus-6, a high-power relativistic repetitively-pulsed electron beam accelerator, is used to drive various slow wave structures in a BWO configuration in vacuum. Peak output power of about 550 MW at 9.45 GHz was radiated in an 8-ns pulse. We describe experiments which study the relative efficiencies of microwave generation from a two-stage nonuniform amplitude slow wave structure and its variations without an initial stage. Experimental results are compared with 2.5 D particle-in-cell computer simulations. Our results suggest that prebunching the electron beam in the initial section of the nonuniform BWO results in increased microwave generation efficiency, Furthermore, simulations reveal that, in addition to the backward propagating surface harmonic of the TM/sub 01/ mode, backward and forward propagating volume harmonics with phase velocity twice that of the surface harmonic play an important role in high-power microwave generation and radiation. >

Fusion-related technology transfer at the Sandia National Laboratories

The technology Transfer Program at Sandia National Laboratories is focused on market pull and rapid commercialization. The emphasis is to apply lab strengths to problems of national importance by partnering with industry and universities with the result of enhancing the US economic competitiveness. The technology transfer of fusion-related technologies enhances the mission of the fusion program at Sandia. The short-term strategy in the Pulsed Power Center at Sandia is to develop teaming arrangements with other Sandia organizations to become participants in existing CRADAs. To that end, they are using the expertise and facilities in fusion-related lasers to participate in CRADAs for laser debridement with Massachusetts General Hospital and laser Light Detection and Ranging (LIDAR) with Mission Research Corporation. In addition, they are working with an existing CRADA partner to use the Quick Silver Code to solve advanced electronic packaging problems. The longer-term strategy is to establish CRADAs in surface treatment of metals with ion beams, deep penetration electron beam welding and food irradiation for disinfestation and sterilization. The strong interest shown by industry in these three areas demonstrates the potential commercial value in high average power electron and ion beam systems.

Microwave/millimeter-wave generation in a counterstreaming-beam-plasma system

Radiation from 8 to 60 GHz is generated by injecting counterstreaming, high-power (up to 50 keV and 4 A) electron beams into an unmagnetized, plasma-loaded waveguide. The radiation is emitted at twice the plasma frequency and is amplitude modulated on the ion plasma frequency time scale. The beam-to-millimeter-wave power conversion efficiency at 31 GHz is ≳0.04%. A turbulence theory model is consistent with the radiation characteristics and power scalings.

Short-lived luminescence of mixed silver halides

Two kinds of excitonic luminescence were investigated for the entire series of solid solutions, AgBr 1− x Cl x , (0 ⪕ x ⪕ 1). The time-resolved spectra observed around 2.5 eV after both pulsed high-power electron beam and N 2-laser irradiations are analyzed in terms of the diffusion-controlled recombination of Frenkel defects Ag 0 i and Ag 2+V - c. It is shown that the effective activation energy of Ag 0 i migration is a linear function of the composition x; and predominantly two kinds of nearest neighbours contribute to this process. The position of maximum of the excitonic molecule luminescence found in mixed monocrystals and fibers reveals a distinctive dependence on the composition x. Its amplitude and half-width correlate with the optical losses in fibers which could be used for their characterization.

Electron beam machining of ceramic green-sheets for multilayer ceramic electronic packaging applications

High power electron beams can be used to machine vias and interconnecting structures in ceramic green-sheets. The advantages of this technology are: direct maskless metallization, noncontact machining of high density via and interconnecting structures of fine dimensions. These features translate themselves into design and development of state of the art multilayer ceramic (MLC) packaging on a quick turn around basis from design to build. Electron beam technology offers accurate machining of three dimensional interconnecting line structures. Vias of aspect ratio > 3 and diameters as small as 30 μm have been fabricated.

A high-power electron beam source based on the superemissive cathode

A robust, high current electron beam, produced by emission from a refractory metal cathode operating in the superemissive mode, is reported. Electron beam current of ≳150 A is produced by a back-lighted thyratron during the conductive phase. Electron energies are several hundred eV and the electron beam has the duration of the discharge pulse. A simple differential pumping scheme has been used to demonstrate extraction of the electron beam into a low pressure (&amp;lt;7 mTorr) region.

Simulation studies of a klystronlike amplifier operating in the 10-100 GW regime

A coaxial drift tube allows propagation of an ultra high-power relativistic electron beam (500 keV, >or=100 kA, 100 ns). The modulation of a large-diameter (12.6 cm) intense, relativistic electronic beam (500 keV, 16 kA) by an external microwave source via particle simulation is studied. The annular beam, enclosed within a coaxial drift tube, is found to be fully modulated by a low-power external RF source at a frequency of 1.3 GHz. It is shown that for such an intense beam, a highly nonlinear interaction takes place at the modulating gap, producing highly coherent bunches of electrons. This finding is similar to earlier research in which such modulations were studied for an intense beam propagating in a hollow drift tube. It is further shown that, unlike the hollow drift tube case, the coaxial configuration is easily scaled to high power. Here, a very large diameter (26 cm) intense beam (460 keV, 100 kA) is fully modulated at 1.3 GHz to obtain 31 GW of RF beam power. >

Observation of screening effect in large-area, cold-cathode diodes

In this work we report the first observation of the screening effect in large-area, cold-cathode diodes. A framing camera was used to observe the formation of emission centers (ECs) on a 200 cm2 velvet emitter. The density of ECs increased as a function of applied magnetic field as predicted. The current per EC decreased as the magnetic field was increased. These phenomena suggest methods of increasing the spatial and temporal uniformity of high-power electron beams.

Laser diagnostics of high-power low-energy electron beams

A complete system able to measure in a nondestructive way the energy spread of a dense and cold electron beam is described. It is based on the analysis of the line width of a laser light back scattered by the electron beam. The system will be implemented on an electron cooling device in construction at the Legnaro Laboratories of INFN. A Monte Carlo code has been used to determine the geometrical and spectral properties of the scattered radiation. Using commercial instrumentation it is possible to measure an energy spread of less than 10−3 in two different energy regions: around 100 keV and from 450 to 700 keV.

Stimulated emission from electron-beam-pumped diphenylbutadiene molecules embedded in a crystalline matrix

Stimulated emission was obtained from a new type of organic crystal, paraterphenyl activated with diphenylbutadiene, pumped by a high-power nanosecond electron beam. The radiation characteristics of the crystal were investigated and compared at various rates of electron-beam and laser excitation. The threshold pump power density in the second case was approximately an order of magnitude lower. The optical stability of the crystal was analyzed.

Magnetic system of the GOL-3 installation

The magnetic system of the GOLD-3 device for studies of plasma heating by high-power relativistic electron beams is described. The main part of the magnetic system is a pulse solenoid with a total length of 7 m and an inner diameter of 15.7 cm. The solenoid consists of 60 multi-turn tape-wound coils. The selenoid magnetic field in the operating regime is 6 T and the maximum achievable magnetic field is 11 T.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>