THz backward wave oscillator for plasma diagnostic in nuclear fusion

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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.