TJ-II:Interferometry

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TJ-II has two interferometry systems for the measurement of the line-integrated density.

The Microwave interferometer

The diagnostic is located in sector B8. The probing beam has an inclination of 18.7º with respect to the vertical and a frequency of 140 GHz, corresponding to a wavelength of λ = 2.14 mm. The diagnostic provides a time trace of the line-integrated electron density (65536 points, sampling rate 100 kHz). The time trace is called 'Densidad2_' in the TJ-II database. The signal is less reliable for high densities (above 2-3 1019 m-3). This time trace is fundamental for machine operation.

Two-colour interferometer

The double wavelength heterodyne interferometer (CO2: 10.6 μm, NdYAG: 1.064 μm) provides values of the plasma line integral density in scenarios with average densities ranging from a few times 1018 m–3 to more than 5×1019 m–3. The results have been compared with those from the 2 mm (microwave) interferometer, obtaining an excellent agreement. Working with a final bandwidth of 4 kHz, a one pass line integral error level about ±2×1017 m–2 has been achieved. [1] [2] [3] [4] [5] [6] The system is located in sector B1.

References

  1. ↑ H. Lamela et al, Laser interferometric experiments for the TJ-II stellarator electron-density measurements, Rev. Sci. Instrum. 72 (2001) 96
  2. ↑ M. Sánchez at al, High resolution CO2 interferometry on the TJ-II stellarator by using an ADC-based phase meter, Rev. Sci. Instrum. 75 (2004) 3414
  3. ↑ P. Acedo et al, CO2 (λm = 10.6 μm) He–Ne (λc = 633 nm) two-color laser interferometry for low and medium electron density measurements in the TJ-II Stellarator, Rev. Sci. Instrum. 75, 11 (2004) 4671
  4. ↑ M. Sánchez et al, Admissible Crosstalk Limits in a Two Colour Interferometers for Plasma Density Diagnostics. A Reduction Algorithm, PLASMA 2007, AIP Conf. Proc. 993 (2008) 187-190
  5. ↑ P. Acedo et al, Calibration of a high spatial resolution laser two-color heterodyne interferometer for density profile measurements in the TJ-II stellarator, Rev. Sci. Instrum. 79 (2008) 10E713
  6. ↑ L. Esteban, M. Sánchez, J.A. López, O. Nieto-Taladriz and J. Sánchez, Continuous plasma density measurement in TJ-II infrared interferometer—Advanced signal processing based on FPGAs, Fus. Eng. Design (2010) in press
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