SHeet Electron beam vacuum eLectronic Devices for the generation of hIGH power THz radiation

THz frequency (300GHz to 1THz) radiation sources are used in a number of diverse applications such as radars, the study of the fundamental properties of materials, security imaging, magnetic resonance spectroscopy, plasma diagnostics, medical imaging and chemical sensing. The power that can be generated from 'bench top' free electron radiation sources in the hundreds of GHz to THz frequency range has been limited by the fact that as the frequency is increased, the size of the interaction region has to be reduced in order to prevent the maser becoming overmoded which results in a loss of the temporal or spatial coherence of the output radiation. As the frequency increases it becomes increasingly difficult (if not impossible) using conventional thermionic cathodes to focus and form high current density, high quality electron beams through the small size interaction region of the THz maser. A pseudospark plasma cathode can overcome current density limitations imposed by thermionic emission as well as being able to generate a sheet electron beam without the need to use an external magnetic field.

A psuedospark-sourced sheet electron beam will be used to power a planar Extended Interaction Klystron Amplifier (EIKA) which is extended in one direction as compared to conventional EIKAs based on a cylindrical electron beam produced by a thermionic cathode. A 12mW, 365GHz signal generated by a solid state source will amplified to 100W by the Pseudospark Sheet beam planar Extended Interaction Klystron Amplifier (PS-EIKA). As no guide magnetic field is required the PS-EIKA will be compact, reliable, robust and can generate 100ns duration pulses at high (kHz) pulse repetition frequencies. In addition a pseudospark source sheet electron beam will be used to drive a planar Extended Interaction Oscillator (EIKO) to generate 10W of output power at 1THz. The proposed research will be conducted jointly by two leading research groups in microwave device engineering with complementary expertise, in Univ. of Strathclyde and QMUL.

Knowledge of pseudospark Extended Interaction Klystron amplifier (PS-EIKA) and oscillator design and construction will be transferred to our Project Partner. A community network of THz amplifier users in magnetic resonance spectroscopy, plasma diagnostics and mm-wave radar applications will be built up to the benefit of future co-created research collaborations. These include the use of the PS-EIKA in Electron Paramagnetic Resonance (EPR) and to improve the sensitivity by many orders of magnitude of Nuclear Magnetic Resonance (NMR) through DNP techniques. The EPR and DNP enhanced NMR (including the possibility of pulsed DNP-NMR and the use of phase and amplitude modulation) experiments will strongly enhance the UK's position as a world leader in a wide range of academic research areas in physics, chemistry, biology, engineering and medicine. These sources are also of national and international importance in the areas of magnetically confined fusion for plasma diagnostics and mm-wave radar systems.

New high power sub-millimetre wave amplifiers and terahertz oscillators will be constructed for radically improved sensitivities in NMR/DNP and EPR instruments in high magnetic fields, enhanced plasma diagnostics and THz imaging. Network activities as part of the proposal will bring together leading groups/industries in the magnetic resonance spectroscopy, microwave plasma diagnostics community and the high power amplifier and microwave/mm-wave source community. Increased capability in these areas as well as enhanced capability to measure fast and slow moving objects using sub-millimetre wave radars will be exploited via our Project Partner. All network members have an outstanding track record in relevant technology and methodology development and all have strong links with National and International applications programs with multiple collaborators across RF and Microwave science and technology application areas.

We believe the proposal has the potential to create impact on an academic, societal and economic level as well as consolidating developing the careers of the researchers in the field of novel amplifiers and oscillators in the sub-millimetre wave and THz band.

The Extended Interaction Klystron Amplifier and Extended Interaction Klystron Oscillator is a technology with potential for high societal impact on a large number of themes, with strong public recognition, such as 1) well-being and longevity of society: through its high sensitivity NMR as methods of biomarkers, imaging and medicine discovery for large numbers of diseases including cancers; 2) high power amplifiers and oscillators for high resolution radar imaging of invading flying objects, 3) security and safety of society: real time security imaging (through clothes and bags) for contrabands such as explosives, illegal drugs,; 4) THz sources for new spectroscopic material measurement technique; 5) understanding of a critical phenomenon such as the anomalous transport of the plasma in fusion energy sources.

A confidential market review highlighted demand and tremendous interest from key opinion leaders in DNP, EPR and a major global instrumentation business showing a demand of up to 50 sub-millimetre wave amplifier systems each year, hence a multi-million pounds per annum high value business proposition. It has huge economic impacts through our links with TMD Ltd, (switched mode power supply manufacturers and vacuum tube manufacturers) who have links to Thomas Keating Ltd (spectrometer and EPR instrumentation) and through academic colleagues in the fields of chemical and biological science. There are also important, significant applications for these terahertz amplifiers in security, radar and material characterisation which will be exploited by our project partner TMD Ltd.