The development of collective scattering diagnostics is essential for understanding of the anomalous transport attributed to short scale length microturbulence
which poses a threat to the development of nuclear fusion reactors. Signals in the sub-THz range (0.1 – 0.8 THz) with adequate power are required to probe the plasma. A joint international effort is therefore devoted to the design and
realization of novel backward wave oscillators at 0.346 THz and above with output power in the 1 Watt range to replace the bulky, high maintenance optically pumped FIR lasers so far utilized for this plasma diagnostic.