Optical technologies towards improving the Far-infrared laser Polarimeter-Interferometer system on HL-2A tokamak

Experimental study of perturbative particle transport in the HL-2A tokamak

“…The parameters in this discharge are as follows: major radius , minor radius , magnetic field , plasma current , and background electron density . Figure 1 shows the temporal evolution of plasma parameters of a typical discharge, where the electron temperature is measured at normalized radius with an electron cyclotron emission (ECE) radiometer [ 14 ] and the line-average density is measured with a far infrared rays (FIR) laser interferometer [ 15 ]. Plasma current is kept stable from 200 ms to 1700 ms.…”

Progress of the synthetic HCOOH laser diagnostic system on HL-2A tokamak

“…The generation of spurious oscillation on Faraday rotation angle can be briefly explained as follows [14,15]: for double-passing Polarimeter, if there is stray light generated in the system, it will go into the detector, together with the probe waves. After signal mixing, the expression of Faraday rotation angle can be written in the form of: α ≈ 2α F − 2ε cos(φ I − φ Is ) × sin φ Fs , where, ε is the ratio of stray light to the signal, φ I and φ Is express the phase shifts related to electron density and stray light, α F and φ Fs are the Faraday rotation angles related to magnetized plasma and stray light.…”

“…In HL-2A experimental campaign, an optic-isolator which was made up of a polarizer and a quarter wave plate was used to suppress the unwanted stray light. The working principle of the optic-isolator can be briefly explained through the figure 5(a) [15], in which the line direction of the…”

An FFT overlap method for high bandwidth far-infrared laser Interferometer in HL-2A

“…Many diagnostic systems are installed in HL-2A to measure the complex MHD fluctuations, such as the magnetic probes [3], electron cyclotron emission (ECE) [4], electrostatic probe system [5], microwave reflectometer [6,7], and so on. MHD instability can cause electron density fluctuations [8,9], which can be captured by electron density diagnostics.…”

“…The frequency distribution of the MHD instabilities ranges from less than 1 kHz to hundreds of kHz [10]. Some density fluctuation frequency, such as reverse shear Alfven eigenmodes (RSAE), can reach above 80 kHz [8,9], while some Low-Frequency Zonal Flows (LFZF) frequency is lower than 4 kHz [11]. Driven by the demand for high-bandwidth electron density diagnostics, the modulation 2021 JINST 16 P09010 signal frequency of the FIR interferometer is upgraded to 1-5 MHz with two methanoic acid lasers [12][13][14].…”