A high wavenumber poloidal scattering system for the NSTX Tokamak

Summary form only given. The NSTX high-k scattering system employs a 282 GHz probe beam, with steerable reflective optics spanning scattering angles in the range of ±20°, with wavenumber coverage up to 30 cm^-1 in k_r and 7 cm^-1 in k_θ.¹ This system has provided a wealth of physics data concerning electron gyroscale fluctuations in the NSTX core.² UC Davis and PPPL propose to develop a new high-k system with expanded physics capabilities including increased sensitivity and a significantly enhanced wavenumber coverage. The new scattering system configuration will employ a vertically extended window on Bay L to take the place of the present Bay K receiver optics and windows which will be removed following the planned installation of a second neutral beam injector following the FY 12 run. The new window, coupled with a launch frequency of 604 GHz, will provide greatly increased poloidal coverage spanning 5 cm^-1to>;25cm^-1. The new FIR launch source will be an FIR laser operating at 496.1 μm generating ~100 mW of probe power. This replaces the ~30 mW solid state source used in the current source, which will retained to supply LO power to the planned 5-8 channel receiver system. Although the amplitude of the scattered signals scales as λ², this is more than offset by the combination of increased probe power (100 mW vs. 30 mW) and increased LO power (30 mW vs. ~3 mW) of the new arrangement. Moreover, Gyro simulations suggest that the current arrangement fails to sample the spectral peak of the ETG fluctuations which dominate the density fluctuations at the NSTX core. The new arrangement could therefore achieve a ~10X increase in scattered signal amplitude when aligned to sample the ETG spectral peak. Details concerning the planned NSTX scattering system upgrade together with a tentative development and installation schedule will be pr- vided.