A new high sensitivity far-infrared laser interferometer for the HL-2A tokamak

Abstract

A new four-chord Michelson-type formic acid (HCOOH, λ = 432.5 μm) laser interferometer has been successfully commissioned on the HL-2A tokamak to measure the electron density and density fluctuations. Due to the employment of the two-laser heterodyne technique, the time resolution of the interferometer reached 1.0 microseconds (μs). Four chords of line electron densities with a line-averaged density resolution 2 × 10/m were obtained in a recent HL-2A experimental campaign, and detailed electron density fluctuations, caused by events such as edge localized mode, sawtooth precursor-oscillations, and energetic particle driven instabilities, were distinctly measured. In particular, the high-frequency electron density fluctuations (up to 500 kHz) caused by the reversed shear Alfvénic eigenmode were observed by the internal two interferometry channels, and their fluctuation location could be approximately identified from the spectra characteristics of multi-chord line electron densities.

Long radial coherence of electron temperature fluctuations in non-local transport in HL-2A plasmas

“…1(a)) is measured using a far-infrared interferometer (FIR). [39] It is evident that the line-averaged density increases immediately after the GPs and then gradually decreases. Simultaneously, the inner core electron temperature exhibits a bulge, followed by a recovery over a duration of approximately 30 ms, while the edge amplitudes undergo opposite changes.…”

Compact phase comparison system for the synthetic HCOOH laser diagnostic system in HL-2A

“…and has achieved remarkable success [16][17][18]. Furthermore, the reverse shear Alfvén eigenmode (RSAE) has been successfully observed in HL-2A using a far-forward collective scattering diagnostic scheme [19].…”

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

“…2015 [11]. This paper introduces recent progress made to improve the diagnostic system, such as promotion of the real-time density feedback control, suppression of the stray light in the Polarimeter, and application of the newly developed far-forward collective scattering diagnostic based on two circularly polarized waves.…”

“…This paper introduces recent progress made to improve the diagnostic system, such as promotion of the real-time density feedback control, suppression of the stray light in the Polarimeter, and application of the newly developed far-forward collective scattering diagnostic based on two circularly polarized waves. Detailed configuration of the HCOOH laser Interferometer is given in [11]. Figure 1 In high performance plasma discharge, one of the important tasks is to control the density at a proper level without plasma disruption occurrence [12].…”

“…HL-2A HCOOH laser Interferometer is able to provide four channels of line-integrated electron densities (Z = −3.5, −10.5, −17.5, −24.5 cm), as well as the density fluctuations, with time resolution of 1.0 µs, spacial resolution of 7.0 cm, and density resolution of 2 × 10 16 /m 3[11].…”