THz backward wave oscillator for plasma diagnostic in nuclear fusion

Terahertz technology and nuclear fusion are two fascinating scientific fields of strategic importance for the scientific progress and a sustainable future. The technological challenges are formidable and require a joint effort at global level.
The Lancaster University leads an ambitious project in collaboration with the University of Leeds and two international partners of the calibre of University of California Davis, US, and Beijing Vacuum Electronics Research Institute, China, to solve the lack of compact, affordable and powerful THz sources required to foster a breakthrough in the understanding of the mechanisms of nuclear fusion and to open new frontiers in many outstanding applications at THz frequency, presently limited only at laboratory level.

Nuclear fusion is unanimously considered as a limitless and clean source of energy of the future. The UK strongly supports national fusion programs as MAST at the Culham Center for Fusion Energy (CCFE) and the ITER project for the first commercial fusion reactor.
Cancer early diagnosis or burn diagnosis, imaging for non destructive quality inspection, food quality analysis, detection of dangerous or illegal substances, high sensitivity receiver for space explorations (about 97% of the space radiation is at THz frequency), wireless communications with the same data rate as multigigabit optical fibres, art conservation and many others are only some of the numerous outstanding applications of THz radiation. Further, the very low energy level (1/100000 in comparison to X-rays) of the THz radiation will not raise the same health concerns as X-rays, making its use acceptable to the general public.
The nuclear fusion process requires extremely high temperatures (more than 100 million degree) for the fuel, a hot plasma, that has to be confined by a proper magnetic field. Unfortunately, due to perturbation causes, the plasma suffers from undesired turbulence that, if too intense, can lead up to the blocking of the fusion reaction. Measurement of plasma turbulence based on THz frequencies is of fundamental importance to define methodologies to strongly reduce the phenomenon.
A team at University of California Davis (UC Davis) led by Prof. Neville Luhmann is realising a novel advanced plasma turbulence diagnostic system based on high-k collective Thomson scattering at THz frequencies to be tested at the National Spherical Torus Experiment (NSTX) at Princeton Plasma Physics Laboratory (PPPL) and of interest to the MAST experiment in UK. The new system will require compact, affordable and powerful (above 100 mW) THz sources. The conventional electronic and photonic approaches fail to provide devices with adequate power and such sources, where available, are very narrow band, weak and expensive.
The recent advances in microfabrication processes have opened new routes in realising micro vacuum electron devices to generate high power at THz frequencies. However, the technological challenges of affordable THz vacuum sources remain formidable.
Lancaster University will lead this project for the realisation of the first compact, powerful, affordable 0.346 THz backward wave oscillator vacuum tube, supported by the outstanding technological facilities at Leeds University, UC Davies and BVERI, and will establish a new low cost fabrication process for fast prototyping assisted design and fabrication of metal microstructures for THz vacuum electron devices in the UK.
This project represents a unique opportunity for UK academia to have a central role in the advancement of the knowledge in two fundamental scientific fields such as THz vacuum electronics and nuclear fusion.
This research is the first step of a long-term joint strategy to develop a new family of compact, low cost THz sources to open new perspective in the THz science in the UK.

Nuclear fusion is one of the most fascinating and complex research fields of our age that attracts the widest interest of scientific and civil society.
In recent years many promises have come from laboratories worldwide claiming outstanding benefits of THz radiation for applications in many fields of great impact to the society such as: plasma diagnostic, healthcare, space exploration, security, imaging, wireless communications, art conservation only to cite a few. In practice however, most of those applications have not reached the market so far, due to the inadequacy of solid state and photonics to provide compact, powerful and affordable THz sources. A new emerging technology, of THz vacuum electronics, offers promising solutions to solve this lack of available power and finally bridge those applications from the laboratories to the market. The blend of THz vacuum electronics and nuclear fusion assures the highest impact for this research.
-Impact to knowledge
This project has a long-term impact of outstanding importance for the understanding of plasma turbulence for nuclear reactor, with great benefit for the MAST in UK and NSTX in USA, key experiments for the realisation of the Component Test Facility for the ITER project. The availability of portable BWOs and vacuum tube amplifiers will permit key investigations into the properties of THz radiation outside the laboratories, opening new research opportunities. The international breadth of the project, gathering top-level academics from the UK, US and China, will boost the mutual collaboration in the emerging field of THz science.
-Impact to people
The broad range of expertise required for the successful achievement of the various targets of the project will involve the education and training of a number of young researchers in strategic disciplines such as electromagnetism, vacuum electronics, micromachining, material science, plasma physics and chemistry.
-Impact to economy
The nuclear fusion is at the early stage of development, but faster progress in the understanding of the plasma dynamics will speed up the realisation of the first working reactors. The huge investment required is a driving theme for many industry sectors with a high benefit to the UK economy. The availability of the proposed new technology will be the first step to create a family of THz vacuum tubes (oscillators and amplifiers) to respond to the industry need of enabling devices for many THz applications, in the 0.1-1 THz range, where only a few THz devices, at a cost exceeding £100k each, are available. A start up will be founded on the model of Calabasazas Creek in US for the production of new generations of compact THz sources. The companies in the field of THz applications (e.g. Teraview, Teratech) could extend their range of products, gaining a high competitiveness. Companies in high-tech production (e.g. BAE, Roll-Royce, E2V, Astrium) would benefit from novel THz imaging, measurements or communications approaches. Healthcare instrument companies (e.g. ScanMed) could realise instruments to exploit the outstanding THz radiation diagnostic capabilities, proved at laboratory level, for the benefit of patients. The non-destructive quality control will reduce the overall cost in many industrial sectors (e.g. pharmacy, packaging, semiconductors).
-Impact in Society
The non-ionising nature of THz radiation will have the greatest impact in many applications, presently based on X-ray, where issues on health concerns are driving conflicting discussions. New, non-invasive instruments will be available for early diagnosis and mapping of some of the most common tumours or for burn diagnostic. Wireless communications will be enabled at multigigabit data rate for a wider diffusion of internet access at a speed presently achievable only by optical fibers. In the security field, a safer and more effective screening can surely relax the concern of operators and travellers at airport check points.