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Design elements and first data from a new Doppler backscattering system on the MAST-U spherical tokamak
T L Rhodes1, C A Michael1, P Shi2
1Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA.
The Review of Scientific Instruments
|December 3, 2022
Summary
A new Doppler backscattering system on the MAST-U spherical tokamak measures plasma turbulence across a wide range of wavenumbers. This advanced system enhances signal-to-noise ratio for improved plasma transport studies.
Area of Science:
- Plasma Physics
- Fusion Energy Research
- Diagnostic Techniques
Background:
- Understanding plasma turbulence is crucial for controlling heat and particle transport in fusion devices.
- Previous diagnostic limitations hindered detailed studies of small-scale turbulence relevant to transport.
Purpose of the Study:
- To introduce and validate a new Doppler backscattering (DBS) system on the MAST-U spherical tokamak.
- To characterize the system's capabilities for probing plasma density turbulence over a broad wavenumber range.
Main Methods:
- Installation and testing of an 8-frequency fixed probe beam DBS system.
- Utilizing novel features for remote control of probed density wavenumber, launched polarization (X/O-mode), and launch angle.
- Achieving density fluctuation wavevector alignment to optimize signal-to-noise ratio (SNR).
Main Results:
- The DBS system successfully probed plasma from the edge to the core.
- Accessible normalized wavenumbers (kθρs) ranged from ≤0.5 to 9, covering key turbulence scales.
- Demonstrated capability to align wavevectors, crucial for accurate measurements.
Conclusions:
- The new MAST-U DBS system is a powerful tool for investigating plasma turbulence.
- Its broad wavenumber coverage and alignment capabilities are vital for studying instabilities driving plasma transport.
- This diagnostic advancement aids research into ion temperature gradient, trapped electron, and micro-tearing modes.
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