A collimated neutron detector for RFP plasmas in MST
W J Capecchi1, J K Anderson1, P J Bonofiglo1
1University of Wisconsin- Madison, Madison, Wisconsin 53706, USA.
The Review of Scientific Instruments
|December 3, 2016
Summary
A new neutron camera reconstructs plasma profiles in the Madison Symmetric Torus. This tool studies fast-ion pressure gradients, crucial for understanding Alfvénic mode instabilities and fast-ion transport in fusion plasmas.
Area of Science:
- Nuclear Fusion Science
- Plasma Physics
- Diagnostic Instrumentation
Background:
- Understanding neutron emissivity profiles is key to studying fast-ion populations in fusion devices.
- Fast-ion pressure gradients are implicated in destabilizing Alfvénic modes, which can transport fast ions.
Purpose of the Study:
- To reconstruct the neutron emissivity profile in the Madison Symmetric Torus using a novel collimated neutron detector.
- To investigate the fast-ion pressure gradient threshold for destabilizing neutral beam-driven Alfvénic modes.
Main Methods:
- Utilizing a scintillator-photomultiplier tube (PMT) system with a defined plasma viewing aperture.
- Employing high-density polyethylene for neutron moderation and a liquid scintillator for directional sensitivity.
- Implementing fast preamplification and 500 MHz digitization to prevent pulse pile-up at high count rates.
Main Results:
- Successfully developed and deployed a neutron camera system for emissivity profile reconstruction.
- The system effectively detects fusion neutrons while mitigating gamma radiation interference.
- The adjustable camera base allows for varied plasma viewing, essential for profile reconstruction.
Conclusions:
- The reconstructed neutron emissivity profile provides direct insight into the fast-ion population.
- This diagnostic capability enables the study of critical fast-ion pressure gradients and their relation to plasma instabilities.
