Initial beam emission spectroscopy diagnostic system on HL-2A tokamak.

Area of Science:

• Plasma physics
• Fusion energy research
• Spectroscopy

Background:

• Understanding plasma turbulence is crucial for magnetic confinement fusion.
• Edge plasma fluctuations significantly impact overall plasma confinement.
• Existing diagnostic methods have limitations in spatial and temporal resolution.

Purpose of the Study:

• To develop and deploy a novel beam emission spectroscopy (BES) system on the HL-2A tokamak.
• To measure local low wavenumber density fluctuations (k⊥ρ < 1) with high spatial resolution.
• To characterize edge plasma properties and poloidal flow velocity fields.

Main Methods:

• Utilizing a 50 kV deuterium heating neutral beam for excitation.
• Employing customized in-vacuum optics for high spatial resolution (Δr ≤ 1 cm, Δz ≤ 1.5 cm).
• Implementing high frequency, high-gain preamplifiers and high quantum efficiency photodiodes for high signal-to-noise ratio.

Main Results:

• A 16-detector channel system (8 radial × 2 poloidal) was installed and tested.
• Measurements covered the radial range r/a = 0.8-1.1.
• Successfully measured edge plasma density fluctuation spectra and poloidal flow velocity fields with high signal-to-noise ratio.

Conclusions:

• The developed BES system is capable of providing high-resolution measurements of edge plasma turbulence.
• The system demonstrates potential for advancing the understanding of plasma confinement in tokamaks.
• Future work will involve further optimization and application to various plasma regimes.