Development of solid state terahertz interferometer for the first plasma on HL-2M tokamak

Area of Science:

• Plasma Physics
• Terahertz Technology
• Fusion Energy Research

Background:

• The HL-2M tokamak requires advanced diagnostics for plasma characterization.
• Existing interferometry methods face challenges with amplitude variations and real-time processing.

Purpose of the Study:

• To develop and implement a novel solid-state terahertz interferometer for the HL-2M tokamak.
• To achieve real-time measurement of electron density and plasma instabilities.
• To overcome limitations of traditional interferometry in dynamic plasma environments.

Main Methods:

• Development of a solid-state terahertz interferometer operating in the 220-325 GHz range.
• Utilizing a phase-locked voltage-controlled oscillator with frequency multiplication for terahertz generation.
• Implementing a field-programmable gate array (FPGA) based phase processor with a novel fast Fourier transform algorithm.
• Employing heterodyne interferometry for phase shift extraction, robust against amplitude variations.

Main Results:

• The interferometer successfully operates in the specified frequency range.
• Real-time electron density display is achieved using the FPGA phase processor.
• A minimum measurable electron density of 10^16 m^-3 was demonstrated.
• Electron density and low-frequency tearing modes were successfully measured during the first experimental campaign.

Conclusions:

• The developed terahertz interferometer is a capable diagnostic tool for fusion plasma research.
• The novel FPGA-based algorithm provides accurate phase shift measurements, unaffected by plasma-induced amplitude changes.
• This technology enhances the understanding of plasma dynamics in tokamaks like HL-2M.