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

A large power water-cooled microwave resonance window used for the electron cyclotron resonance (ECR) ion source is investigated in this paper. The microwave characteristic simulation, thermal analysis, and structure design are deeply and successively carried out before fabrication. After the machining and welding of the components, the window is cold and hot tested. The application results demonstrate that when the input power is 2000 W, the reflected power is only 5 W. The vacuum is below 10−10 Pa, and the high power microwave operation can last 30 h continuously and reliably, which indicates that the design and assembling can achieve the high efficiency of the microwave transmission. Finally, the performance of the ECR ion source is enhanced by the improvement of the injected microwave power to the ECR plasma.

Investigation of a large power water-cooled microwave resonance window for application with the ECR ion source

A novel approach to extract and amplify the third harmonic of electron beam to generate high-power terahertz radiation is presented. Three planar grating structures operating in the backwave region are used for the extraction and amplification of the electron beam from the fundamental modulation, the fundamental amplification, and the third harmonic. This results in an amplified output of the fundamental wave and a high power output of the fundamental triplet frequency. The planar grating structure is easier to machine and assemble than conventional harmonic amplifiers and increases the flow rate of the electron beam. Calculations show that with an input signal of 119.5–120.6 GHz at 80 mW and a 35-A/cm2 electron beam in adjustment from 27.5 to 29.3 keV, the structure has an output signal of hundreds of milliwatts in the range of 358.5–361.8 GHz, with a power output of 583.2 mW at the central frequency point of 360 GHz. The harmonic signal is output while a watt-level fundamental signal can be output.

Electron Beam Third Harmonic Amplification Generates High-Power Tunable Terahertz Radiation

In this paper, a 3-D multistage depressed collector simulation program is studied and developed, which consists of electrostatic potential calculation, electron trajectory tracking, space charge density calculation, secondary electron emission model, etc. To benchmark this multistage depressed collector simulation program, an identical model created by CST was used for comparison. Several different sets of voltage settings were used to compare with and without secondary electrons emission, and then electron trajectories are plotted. The comparison includes collector simulation efficiency and back-streaming rate. This program uses interface design and easy to use, which is a good method to assist the design of multistage depressed collector.

Development of A 3-D Multistage Depressed Collector Simulation Program

The all-mental double corrugated waveguide slow wave structure has potential to produce high power THz radiation. This paper presents a terahertz backward wave tube with double corrugated waveguide SWS in consideration of the surface loss and the cathode's emittance. To reduce the size and weight, a wedge attenuator is assembled at the end of the backward wave tube. The dispersion characteristics and the interaction impedance of the slow wave structure are studied in detail and optimized. The beam-wave interaction is simulated with CST Particle Studio. The results show that this backward wave tube can produce over 0.16-W output power at the frequency of 0.36THz. The THz sheet beam backward wave tube will be fabricated and tested in the near future.

THz sheet beam backward wave tube with double corrugated waveguide slow wave structure

Slow wave structure employed in a wide-band helix traveling wave tube (TWT) always support backward waves. A backward wave space harmonic of a signal at a harmonic of the drive signal can effectively interact with slow space-charge wave of an electron beam. The minus first space harmonic is in synchronism with the beam at some frequencies. As a consequence, the backward wave can compete with the forward wave and it results in the backward wave oscillation (BWO) power holes under large signal conditions. In this talk, we reported a study of BWO power holes in both simulations and experiments, and developed a step helix pitch method to suppress the BWO power hole.

Yanyu Wei

Papers

Investigation of a large power water-cooled microwave resonance window for application with the ECR ion source

Electron Beam Third Harmonic Amplification Generates High-Power Tunable Terahertz Radiation

Development of A 3-D Multistage Depressed Collector Simulation Program

THz sheet beam backward wave tube with double corrugated waveguide slow wave structure

Study of BWO power holes in helix traveling wave tubes