The NSTX upgrade has provided the impetus to redesign and improve the High-k Scattering System. Improvements will include increased kθ coverage to target Electron Temperature Gradient (ETG) modes. Improved kθ resolution is realized by increasing the probe frequency from 280 to 693 GHz. Current solid state sources cannot deliver sufficient power at this frequency. Availability of current sources is limited to about 300 GHz and 30 mW; therefore, an optically pumped Far Infrared (FIR), formic acid laser has been chosen which can deliver upwards of 100 mW at 693 GHz. A second high frequency source is needed to provide local oscillator (LO) power for an array of quasi optical mixers. Additional lasers are not desirable since they will add complexity to the system. We propose to design and build a 346 GHz Backward Wave Oscillator (BWO) for use with subharmonic mixers. Simulations predict that average output power of 1 W is achievable. Circuit dimensions on the order of 100 microns, with submicron tolerances, make the fabrication of the slow wave structure especially challenging. UC Davis will use nano CNC machining technology to construct the slow wave structure. Additional work includes assessing the feasibility of scaling down this BWO for 600+ GHz operation and/or employing a frequency doubler for higher frequency applications.