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Measuring the Time-Evolution of Nanoscale Materials with Stopped-Flow and Small-Angle Neutron Scattering
Published on: August 6, 2021
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The large helical device vertical neutron camera operating in the MHz counting rate range
K Ogawa1, M Isobe1, T Nishitani1
1National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Japan.
The Review of Scientific Instruments
|December 4, 2018
Summary
A new vertical neutron camera (VNC) was installed on the Large Helical Device (LHD) to measure neutron emission profiles. This advancement enhances understanding of energetic particle transport in fusion plasmas.
Area of Science:
- Nuclear Fusion Energy
- Plasma Physics
- Particle Accelerators
Background:
- Neutrons in neutral beam (NB)-heated deuterium plasma experiments are primarily from beam-plasma reactions.
- Understanding beam ion transport requires time-resolved neutron emission profile measurements.
- Stellarator/heliotron devices lacked dedicated neutron cameras for such diagnostics.
Purpose of the Study:
- To develop and implement a Vertical Neutron Camera (VNC) for time-resolved radial neutron emission profile measurements.
- To enable detailed studies of energetic particle transport in Large Helical Device (LHD) plasmas.
- To establish a novel diagnostic for stellarator/heliotron research.
Main Methods:
- Installation of a VNC on the LHD, featuring a multichannel collimator and fast-neutron detectors.
- Utilizing stilbene crystals and photomultipliers for high-count rate neutron detection with gamma discrimination.
- Development of a digital-signal-processing based data acquisition system (DAQ) with 1 GHz sampling rate.
- Employing hematite-doped heavy concrete for collimator shielding against neutrons and gamma-rays.
Main Results:
- Successful acquisition of neutron emission profiles during the LHD's 2017 deuterium campaign.
- Measurement of profiles in tangentially co-injected NB-heated plasma with varying magnetic axis configurations (Rax).
- Observed increased neutron counts in inward-shifted configurations, consistent with total neutron rates.
- Demonstrated successful radial profile measurement, with peak positions correlating to Rax changes.
Conclusions:
- The Vertical Neutron Camera (VNC) performed successfully as designed, meeting its diagnostic objectives.
- The VNC is a crucial new tool for advancing energetic particle physics studies in LHD.
- This diagnostic capability is the first of its kind for stellarator/heliotron devices, opening new research avenues.
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