High resolution gamma-ray spectrometer with MHz capabilities for runaway electron studies at ASDEX Upgrade

Area of Science:

• Plasma physics
• Nuclear fusion
• High-energy particle physics

Background:

• Runaway electrons pose a significant challenge in tokamak fusion devices.
• Understanding runaway electron behavior is crucial for mitigating disruption effects.
• Existing diagnostic tools have limitations in characterizing high-energy runaway electrons.

Purpose of the Study:

• To develop and validate a novel gamma-ray spectrometer for analyzing MeV runaway electrons.
• To measure the bremsstrahlung emission spectrum generated by runaway electrons during plasma disruptions.
• To infer properties of runaway electrons, such as maximum energy and velocity space distribution.

Main Methods:

• Development of a gamma-ray spectrometer with MHz capabilities.
• Measurement of bremsstrahlung emission spectra from runaway electrons.
• Application of a deconvolution technique to analyze the spectral data.
• In-situ detection during massive gas injection and resonant magnetic perturbation experiments.

Main Results:

• The spectrometer successfully measured bremsstrahlung emission spectra in the gamma-ray energy band.
• Deconvolution of spectra provided insights into runaway electron properties, including maximum energy.
• Distinct changes in the runaway electron velocity space were observed.
• The detector unambiguously identified alterations in electron behavior during different disruption mitigation scenarios.

Conclusions:

• The new MHz gamma-ray spectrometer is an effective tool for studying MeV runaway electrons.
• The instrument provides valuable data for understanding disruption physics and runaway electron dynamics.
• Observed changes in electron velocity space offer critical information for fusion device operation and safety.