Abstract-Backward wave oscillator for high power generation at THz frequencies

Diana Gamzina,  Xiang Li,  Christian Hurd,  Ye Tang,  Xuejiao Huang,  Yuan Zheng,  Logan Himes, Michelle Gonzalez,  Hanyan Li,  Pan Pan,  Rosa Letizia,  Jinjun Feng, Neville C. Luhmann, Claudio Paoloni,


https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10383/1038303/Backward-wave-oscillator-for-high-power-generation-at-THz-frequencies/10.1117/12.2273256.short



The progress in microfabrication techniques and three dimensional electromagnetic simulations have enabled the fabrication of vacuum electron devices up to 1 THz. In particular, the backward wave oscillator is a compact and powerful THz vacuum source, based on the transfer of energy from an electron beam to an electromagnetic (EM) wave propagating in a slow wave structure. The paper reports the design and fabrication challenges to realize a near-THz Backward Wave Oscillator for plasma diagnostics in nuclear fusion. In particular, the beam optics and confinement as well as the slow wave structure are described. Manufacturing as well as device implementation and demonstration considerations are discussed. The double corrugated waveguide is used with a cylindrical electron beam producing an output power on the order of 1 W.

© (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-The 2017 terahertz science and technology roadmap

Conceptual illustration of a THz vacuum electron amplifier (image taken from The 2017 terahertz science and technology roadmap S S Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001. Copyright IOP Publishing Ltd 2017. All rights reserved.)

S S Dhillon1, M S Vitiello2, E H Linfield3, A G Davies3, Matthias C Hoffmann4, John Booske5, Claudio Paoloni6, M Gensch7, P Weightman8, G P Williams, et. al. 

 http://iopscience.iop.org/article/10.1088/1361-6463/50/4/043001

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.

New Terahertz Plasma Diagnostic System for Nuclear Fusion Reactors

By Will Soutter

http://www.azom.com/news.aspx?newsID=42606

Engineers at Lancaster University are reinventing the vacuum tube to produce Terahertz signals to monitor plasma turbulence in nuclear fusion reactors.

The Engineering and Physical Sciences Research Council (EPSRC) has provided £450,000 for the study, which is being done by a collaborative group including researchers from the University of Leeds, the Beijing Vacuum Electronics Research Institute and the University of California Davis.

 “The device developed by this project will result in a novel plasma diagnostic system which is fundamental for the future development of nuclear fusion reactors, potentially leading to a breakthrough in nuclear fusion techniques."

Professor Claudio Paoloni   

Nuclear fusion is one of the cleanest forms of energy possible, and it could provide an almost inexhaustible supply of energy. However, getting practical fusion reactor running is extremely difficult to achieve. It requires temperatures exceeding 100 million °C for the fusion reaction to take place, and a strong magnetic field to contain the fusion plasma.

During the fusion reaction, unwanted turbulence may take place, which could disrupt the plasma enough to slow the reaction or prevent it taking place altogether - leading to a loss of energy, or even hazardous containment issues.

Terahertz vision

Terahertz waves possess specific properties which enable them to non-destructively penetrate different types of materials. They hold promise for use in practical nuclear fusion reactions, as terahertz radiation can help understand plasma behavior without greatly disturbing the delicate fusion material.

Previously, research into the applications of terahertz radiation has covered detection of explosives, analysis and restoration of artistic masterpieces, and diagnosis of cancer. The technology has been limited to laboratories, however, as the techniques used require powerful terahertz sources, which are typically very large in size.

The old and the new

The team of researchers intends to develop a powerful, compact and cost-effective powerful Terahertz vacuum electron device by using the latest microfabrication processes to allow traditional vacuum tubes to reach terahertz frequencies.

The device being built would be installed at the nuclear fusion test facility in Princeton (the National Spherical Torus Experiment) and would become the main part of the plasma diagnostic system. The new device would enable commercialization of the technology by taking it from the laboratory to the market.

T-rays' electronics to shed light on nuclear fusion

http://www.nanowerk.com/news2/green/newsid=37667.php

(Nanowerk News) In the race to secure clean energy in the future, Lancaster University Engineers are reinventing a piece of technology which has so far only been used in labs to diagnose cancer, detect explosives, and even analyse grand artistic masterpieces.

Working with world-leaders in their field, researchers will employ modern microfabrication processes to bring vacuum tubes - born at the beginning of the electronics era - up to Terahertz frequencies (hundreds of GHz), which they hope will bring about a breakthrough in the understanding of the mechanisms of nuclear fusion.

Nuclear fusion, considered to be a potential future option for a clean and inexhaustible energy supply, requires extremely high temperatures (more than 100 million°C) for the fuel, a hot plasma that has to be confined by a proper magnetic field. Unfortunately, this plasma can suffer from undesired turbulence that, if too intense, can block the fusion reaction, resulting in energy loss or, in a worst case scenario, melt the metal wall of the reactor. Only Terahertz radiation can provide an accurate insight into plasma behaviour without perturbing this extremely delicate material.

Terahertz waves (or T-rays) have unique properties as they can penetrate many materials without damaging them. In recent years, Terahertz radiation has been put to use in fields as diverse as cancer early diagnosis, airport security and fine art restoration. But until now, Terahertz technology has been largely confined to the laboratory because of the lack of compact and powerful sources.

Funded by the Engineering and Physical Sciences Research Council, the £450,000 research project brings together an international team of researchers including the University of Leeds, the University of California Davis, US, and the Beijing Vacuum Electronics Research Institute, China.

Once built, the device will be the core of the plasma diagnostic, led by Professor Neville C. Luhmann, University of California Davis, US, to be installed at the National Spherical Torus Experiment (NSTX), a nuclear fusion test facility at Princeton US.

Lancaster University’s Professor Claudio Paoloni said: "Considering that 60kg of fuel for nuclear fusion can produce an energy equivalent to 250,000 tons of oil, it is a very important technology for the future provision of clean, reliable energy. However, to do this efficiently and safely, a reliable new way of monitoring plasma turbulence is needed.

"The device developed by this project will result in a novel plasma diagnostic system which is fundamental for the future development of nuclear fusion reactors, potentially leading to a breakthrough in nuclear fusion techniques.

"Ultimately, by developing a compact, affordable and powerful Terahertz vacuum electron device we will demonstrate that it can have a formidable impact at a commercial level. By taking Terahertz technology out of the laboratory and into the real world, we will finally enable many other fundamental applications to take a step forward in fields from healthcare and security to food analysis and even art."

He added: "I am very excited to face this challenging project with scientists of the highest calibre including Professor Neville C. Luhmann, Jr., University of California Davis, US, a pioneer in the field of Terahertz vacuum electron devices and leader of the plasma diagnostic development for the NSTX experiment at Princeton University, Professor Jinjun Feng, Vice Director of the most important Chinese research institute on vacuum electronics, and Dr Paul Steenson of the University of Leeds."

Source: Lancaster University