ISTTOK Diagnostics

An overview of the main diagnostics existing in ISTTOK is given in this article. Most of them are available on the scientific literature so you can not expect a very deep insight on each one.

Interferometer

Fig. 1 - ISTTOK interferometer based on the heterodyne detection principle.

The ISTTOK interferometer is based on the heterodyne detection principle with quadrature detection for an absolute phase determination and has only one vertical line of sight that crosses the plasma in the radial center. The interferometer uses a central frequency of 100 GHz, crossing the plasma central cord. It can be used to measure densities up to 1.24 x 10^20 m-3. The signal from the RF oscillator and the same signal after crossing the plasma are then mixed with the local oscillator frequency (99.15GHz), resulting in an interference frequency of 850 MHz. Although more complex, this method with a intermediate frequency generation has the advantage of reducing the frequency to be acquired by the data acquisition system and improves the sensibility of the system. After the phase unwrapping one can retrieve the average plasma density across this cord.