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Published on: February 22, 2018
Fast-particle-driven Alfvénic modes in a reversed field pinch
J J Koliner1, C B Forest, J S Sarff
1Physics Department, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA. koliner@wisc.edu
Physical Review Letters
|September 26, 2012
Summary
Alfvénic modes were observed in reversed field pinch plasma during neutral beam injection. These modes are driven by fast ions, leading to a switch from n=5 to n=4 modes.
Area of Science:
- Plasma Physics
- Fusion Energy Research
Background:
- Reversed Field Pinch (RFP) plasma experiments often exhibit complex magnetohydrodynamic (MHD) instabilities.
- Neutral beam injection (NBI) is a key technique for plasma heating and current drive in fusion devices.
Purpose of the Study:
- To investigate the occurrence and characteristics of Alfvénic modes driven by NBI in an RFP plasma.
- To understand the underlying mechanisms responsible for the observed mode behavior and transitions.
Main Methods:
- Experimental observation of plasma response to NBI.
- Computational modeling of neutral beam deposition, slowing down, and resulting plasma profiles.
- Analysis of mode frequencies, toroidal mode numbers, and scaling with plasma parameters.
Main Results:
- First observation of Alfvénic modes in an RFP plasma due to NBI.
- High velocity and radial localization of deposited fast ions identified as crucial.
- Instability drive mechanisms identified as inverse Landau damping and fast ion density gradients.
- Observed mode switching from a lower frequency n=5 mode to a higher frequency n=4 mode with Alfvénic scaling.
Conclusions:
- NBI can drive Alfvénic instabilities in RFP plasmas.
- Fast ion properties, including velocity and radial distribution, are critical for instability.
- Mode dynamics are influenced by beam parameters, leading to observable frequency and mode number transitions.
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