Do you design and build vacuum electron devices, or work with the systems that use them? Quickly develop a solid understanding of how these devices work with this authoritative guide, written by an author with over fifty years of experience in the field. Rigorous in its approach, it focuses on the theory and design of commercially significant types of gridded, linear-beam, crossed-field and fast-wave tubes. Essential components such as waveguides, resonators, slow-wave structures, electron guns, beams, magnets and collectors are also covered, as well as the integration and reliable operation of devices in microwave and RF systems. Complex mathematical analysis is kept to a minimum, and Mathcad worksheets supporting the book online aid understanding of key concepts and connect the theory with practice. Including coverage of primary sources and current research trends, this is essential reading for researchers, practitioners and graduate students working on vacuum electron devices.

Microwave and RF Vacuum Electronic Power Sources

The author presents a bibliography covering the field of electrical discharges in vacuum, comprising both electrical breakdown in vacuum and vacuum arcs. A brief section lists some review papers which would be helpful to the novice in this field. The bulk of the presentation consists of bibliographic listings arranged by year of publication and alphabetically by author within each year. An author index refers one to all papers authored or coauthored by a particular person. >

Electrical discharges in vacuum: 1980-90

Radio frequency (RF) breakdown can result in pulse shortening and severely limits the performance of high-power microwave (HPM) generators. In this paper, the initial stage of RF breakdown in HPM generators with a strong external guiding magnetic field has been carefully analyzed. It is thought that the initial breakdown process involves electron emission induced by an intense local field, electron acceleration in the electric field, and electron bombardment on the structure’s surfaces. Strong external guiding magnetic fields play a key role in the RF breakdown process of HPM generators. They concentrate the impact energy and make it more destructive. To suppress RF breakdown, feasible solutions include lowering the local field strength, decreasing the energy of the field-emitted electrons obtained from the RF field, reducing the deposited energy density, and improving the material’s resistance to electron bombardment.

RF Breakdown of the Resonant Reflector in a Relativistic Backward Wave Oscillator

The various phenomena which limit the operating voltage of klystrons are described. These include gun arcing, Kilpatrick's criterion for r-f gap arcing, and cavity r-f power density. Factors affecting beam current such as space-charge effects, pulse length, and beam tunnel area are also examined. The peak power capability of klystrons may be described as a function of wavelength by two overlaid sets of curves in which operating voltage, perveance and pulse length are parameters. The average power capabilities and scaling laws for various single-mode-waveguide output windows are described. The theoretical limits described above correlate well with power levels reached by existing klystrons and predict directions for development of much more powerful klystrons. The limits described apply not only to conventional klystrons, Out also to Clustered-CavityTMKlystrons, so it is possible to consider the development of multimegawatt or even gigawatt klystrons with bandwidths in excess of 30%.

Scaling laws and power limits for klystrons

The article begins with a brief review of the achievements of Russian tokamaks in the active period of their development from 1962 to 1973, under the leadership of academician L.A. Artsimovich. During these years, the following basic issues were solved: the equilibrium problem, the MHD stability of the plasma column, and creation of the hot plasma with intense DD neutron radiation. It was shown that the ion confinement in tokamaks is close to the neoclassical model, and the electron confinement is abnormal. It improves with the increasing frequency of collisions, the opposite of the case with ions, in what is known as the alternative model of confinement along the magnetic field. Finally, the first scaling law for the energy lifetime of plasma was obtained, which accurately predicted the plasma parameters of the next generation of tokamaks (the so-called T-4 scaling). The subsequent movement in this direction (the 'Artsimovich vector') led to the creation of DT reactors with a fusion power of up to 10 MW (TFTR, JET) and to the ITER project. The main objective of the further development of tokamaks is their transition to steady-state fusion operation, which is a prerequisite for their use in industrial power generation. This makes it necessary to re-evaluate the achievements and obstacles that have to be overcome. The first limitation which thus arises is the so-called P H/S limit, which limits the value of the plasma heating power in a tokamak, as well as the discharge duration ▵t (the 'TRIAM vector') in current tokamaks (▵t ~ 1/(P H/S)1.7). Analysis of the existing experimental data shows that the most probable reason for the limitation of P H in existing tokamaks is the breakdown of the plasma sheath in the places of direct contact of the plasma with the wall. The reason for limiting the discharge duration ▵t may be the gradual accumulation of the erosion products in the contact zones of the plasma with the tokamak first wall, which can facilitate such a breakdown. Creating a closed circulating lithium flow between the first wall and plasma is proposed as the solution to the problem of accumulation of the products of the first wall erosion. Preliminary studies (appendices A and B) have shown that the undesirable accumulation of tritium in the protective lithium films can be avoided if the temperature of the wall of the tokamak discharge chamber does not exceed 400 °C.

https://iopscience.iop.org/article/10.1088/1741-4326/aaee92/pdf

Tokamak evolution and view to future

A new high-voltage scaling based on Kilpatrick's criterion is presented that suggests that voltages more than twice the Kilpatrick limit can be obtained with identical initial conditions of vacuum and surface cleanliness The calculations are based on the experimentally observed decrease in secondary electron emission with increasing ion impact energy above 100 keV A generalized secondary-emission package has been developed to simulate actual cavity dynamics in conjunction with our 2?-dimensional fully electromagnetic particle-in-cell code CEMIT The results are discussed with application to the suppression of vacuum breakdown in rf accelerator devices

/pdf/criteria-for-vacuum-breakdown-in-rf-cavities-512dukk5by.pdf

Criteria for Vacuum Breakdown in RF Cavities

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Criteria for Vacuum Breakdown in RF Cavities