29th Symposium on Fusion Technology (SOFT 2016)

P2.056 2-mm microwave interferometer for COMPASS tokamak

Sep 6, 2016, 2:20 PM

1h 40m

Foyer 2A (2nd floor), 3A (3rd floor) (Prague Congress Centre)

Board: 56

Poster D. Diagnostics, Data Acquisition and Remote Participation P2 Poster session

Speaker

Mykyta Varavin (Institute of Plasma Physics AS CR)

Description

The COMPASS tokamak is equipped by the 2-mm microwave interferometer. This interferometer measures the electron density integrated along the central chord. Two VCO oscillators stabilized by the PLL together with multipliers generate two probing waves of the close frequency 139.3 and 140 GHz. The digital 2π-phase detector in the receiving part compares the phase between these probing waves. The resulting differential phase shift is 200 times smaller than the probing waves themselves. Therefore the phase response does not suffer from fringes for the full range of COMPASS electron density, which is more than 12x10¹⁹19 m^-3-3. Both real-time and post-processed electron density take into account the interferometer line-of-sight, i.e. plasma shape, and correction to the non-linearity of the refractive index of the plasma. This way, the line-averaged electron density is obtained. The real-time signal is used for the electron density feedback.