Abstract A time resolved radial profile neutron diagnostic is being designed for the National Spherical Torus Experiment (NSTX). The design goal is to achieve 5-7 cm radial resolution while minimizing the mass of the shielding. Experiments with a calibration neutron source have been performed to determine the dimensions and material composition of a collimating device needed to reduce cross-talk between channels and contributions from stray particles to acceptable levels. The well established MCNP transport code has been used to simulate attenuation and scattering. The laboratory experiment measuring attenuation through borated polyethylene, lead, and stainless steel has been simulated to determine optimal shielding around the detector. A model of a test collimator was produced, and the most effective dimensions for apertures was examined. Experimentally, the e- folding distance in borated polyethylene, the primary shielding candidate, was found to be 12 cm, but computer simulation found it to be 20 cm. Better agreement was found in the attenuation study where computer simulation correctly approximated the slope of the curve within a few percent. Best results were obtained from the simulation of the collimator when MCNP exactly mimicked experimental results. This result gives confidence in MCNP for Supported by US DoE contract DE-AC02- 76CH03073.
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Abstract A time resolved radial profile neutron diagnostic is being designed for the National Spherical Torus Experiment (NSTX). The design goal is to.
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AbstractA time resolved radial profile neutron diagnostic is being designed for the National Spherical Torus Experiment (NSTX). The design goal is to achieve 5-7 cm radial resolution while minimizing the mass of the shielding. Experiments with a calibration neutron source have been performed to determine the dimensions and material composition of a collimating device needed to reduce cross-talk between channels and contributions from stray particles to acceptable levels. The well established MCNP transport code has been used to simulate attenuation and scattering. The laboratory experiment measuring attenuation through borated polyethylene, lead, and stainless steel has been simulated to determine optimal shielding around the detector. A model of a test collimator was produced, and the most effective dimensions for apertures was examined. Experimentally, the e-folding distance in borated polyethylene, the primary shielding candidate, was found to be 12 cm, but computer simulation found it to be 20 cm. Better agreement was found in the attenuation study where computer simulation correctly approximated the slope of the curve within a few percent. Best results were obtained from the simulation of the collimator when MCNP exactly mimicked experimental results. This result gives confidence in MCNP for future use. Much has been learned about materials and dimensions, so design of a neutron collimator can begin with more working knowledge as a guide.
Supported by US DoE contract DE-AC02-76CH03073.
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Goals
• Design of a neutron profile detector– Seven channels– 5-7 cm radial resolution– At most 1ms time resolution
• Determine if signal will be sufficient
• Analyze possibility of back scattering and detector cross-talk