Review of Charged Particle Dynamics. Beam Optics and Focusing Systems Without Space Charge. Linear Beam Optics with Space Charge. Self-Consistent Theory of Beams. Emittance Variation. Beam Physics Research from 1993 to 2007. Appendices. List of Frequently Used Symbols. Bibliography. Index.

Theory and Design of Charged Particle Beams

Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

The 2016 terahertz science and technology roadmap

Bibliometric data set the scene by illustrating the growth of terahertz work and the present interest in terahertz science and technology. After locating terahertz sources within the broader context of terahertz systems, an overview is given of the range of available sources, emphasizing recent developments. The focus then narrows to terahertz sources that rely on surface phenomena. Three are highlighted. Optical rectification, usually thought of as a bulk process, may in addition exhibit a surface contribution, which, in some cases, predominates. Transient surface currents, for convenience often separated into drift and diffusion currents, are well understood according to Monte Carlo modelling. Finally, terahertz surface emission by mechanical means—in the absence of photoexcitation—is described.

https://iopscience.iop.org/article/10.1088/0022-3727/47/37/374001/pdf

A review of terahertz sources

This paper presents a comprehensive theory of the cyclotron resonance maser (CRM) interaction in a circular waveguide. The kinetic theory is used to derive the dispersion relationships for both TE and TM modes. The TE mode case has been investigated by several authors, but there has been comparatively little work on the TM mode case. However, the TM mode interaction competes effectively with the TE mode interaction at relativistic electron energies. The conditions for maximum temporal and spatial growth rates are shown. The TM mode growth rates are found to vanish when the RF wave group velocity equals the beam axial velocity (‘grazing incidence’). The single particle theory is used to derive a compact set of self-consistent non-linear equations for the TE and TM mode interactions. These equations are particularly appropriate for the cyclotron auto-resonance maser (CARM) regime but applicability extends to other regimes as well. The conditions for optimum efficiency are investigated for oscillator and amp...

Linear and nonlinear theory of the Doppler-shifted cyclotron resonance maser based on TE and TM waveguide modes

We report on hot test measurements of a wide-bandwidth, 220-GHz sheet beam traveling wave tube amplifier developed under the Defense advanced research projects agency (DARPA) HiFIVE program. Nano-computer numerical control (CNC) milling techniques were employed for the precision fabrication of double vane, half-period staggered interaction structures achieving submicrometer tolerances and nanoscale surface roughness. A multilayer diffusion bonding technique was implemented to complete the structure demonstrating wide bandwidth (>50 GHz) with an insertion loss of about −5 dB achieved during transmission measurements of the circuit. The sheet beam electron gun utilized nanocomposite scandate tungsten cathodes that provided over 438-A/cm2 current density in the 12.5:1 ratio sheet beam. An InP HBT-based monolithic microwave integrated circuit preamplifier was employed for TWT gain measurements in the stable amplifier operation region. In the wide-bandwidth operation mode (for gun voltage of 20.9 kV), a gain of over 24 dB was measured over the frequency range of 207–221 GHz. In the high-gain operation mode (for gun voltage of 21.8 kV), over 30 dB of gain was measured over the frequency range of 197–202 GHz. High-power tests were conducted employing an extended interaction klystron.

Performance of a Nano-CNC Machined 220-GHz Traveling Wave Tube Amplifier

We present a novel radiation scheme with an electron beam travelling over a finitely thick slab made of negative-index materials. Such a scheme could start oscillating from Cherenkov radiation without external reflectors, since the electromagnetic energy flows backward inside the negative-index materials, leading to inherent feedback. We theoretically analyzed the mechanism of beam-wave interaction, and designed the negative-index material.

http://ieeexplore.ieee.org/iel7/7301993/7327382/07327759.pdf

Study on radiation source with negative-index materials

Since Klystron simulation code KlyC was released in 2017, it has been used for the design of series of high efficiency (HE) Klystron projects. Lots of new features such as coupling mode analysis, monotron diagnosis and complete small signal theory have been implemented into KlyC to facilitate sophisticated Klystron design. Nevertheless, Standing wave (SW) mode pattern is prerequisite condition in the beam-wave interaction analysis in well-established KlyC large signal simulations. In this report, the latest progress on upgrading KlyC by introducing Traveling-wave (TW) module is demonstrated for future analysis on TW or SW/TW hybrid device. It is proved that extended interaction Klystron (EIK) is still based on SW analysis so that for hybrid device development, pure Traveling wave (TW) module implementation is still necessary and essential. TW circuit model is then adopted in terms of the field excitation, based on which 2 types of exemplary TW tubes are simulated in updated KlyC. Benchmark results with CST PIC show that the accuracy could reach 5% level, taking advantage of KlyC's capability to precisely modeling the space charge effects, relativistic effects and radial stratification effects.

Yanyu Wei

Papers

Study on radiation source with negative-index materials

KlyC expansion: Traveling wave module in Klystron simulation code