A new dispersion interferometer on HL-2A

Abstract

In order to avoid a fringe jump caused by high plasma density and pellet injection [Y. Zhou et al., Rev. Sci. Instrum. 87, 11E107 (2016)], a new CO dispersion interferometer is designed and commissioned on HL-2A for average line-density measurement and density feedback control. The second harmonic technology in this system eliminates the phase shift caused by mechanical vibration. Signals are processed by a digital phase comparator and can be monitored in real time. A series of experiments are conducted to study the characteristics of the system such as a second harmonic coefficient and long-term stability. The resolution of density measurement is less than 8 × 10/m, and the experiment result on HL-2A demonstrates the interferometer's capability to track plasma density evolution with rapid change. The system also shows good stability against mechanical vibrations.

Recent Progress on dispersion interferometers for nuclear fusion and low-temperature plasmas

“…Additional methods to extract the phase difference from the modulated interference signal also exist. Some DIs [13][14][15][16][17][18] evaluate the phase difference from a ratio of amplitudes of fundamental and second harmonic components of the drive frequency ω m . Eq.…”

“…For the phase matching, one uses conventional birefringence of a nonlinear material, the other uses the periodic domain inversion structure. For 10 µm wavelength, the former used for the DIs are ZnGeP 2 [11], AgGaSe 2 [13][14][15][16][17][18], and AgGaS. The latter is OP-GaAs [21,22,27,28].…”

Plasma Density Measurement on an SCU-PSI Device via a CO₂Dispersion Interferometer

“…The diagnostic system on the device includes a Rogowski coil to measure the plasma current, a high-speed camera to measure the diameter of the plasma beam, and a new short-wavelength DI system to measure the plasma density. Figure 2 shows the basic principle of the new DIs [2,[5][6][7][8][9][10]. The CO 2 laser emits a probe beam with a frequency of ω and a vertical polarization.…”

“…The size of the crystal is 5 mm × 5 mm × 15 mm. The conversion efficiency of the crystal is approximately 1 × 10 −6 [2].…”

“…The light source of the DI system is a 10.6-µm CO 2 laser. The system is capable of measuring the plasma density with rapid changes in the pellet injection and is insensitive to mechanical vibrations [2].…”