10 research outputs found

    Neutron Energy Spectrum Measurements with a Compact Liquid Scintillation Detector on EAST

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    A neutron detector based on EJ301 liquid scintillator has been employed at EAST to measure the neutron energy spectrum for D-D fusion plasma. The detector was carefully characterized in different quasi-monoenergetic neutron fields generated by a 4.5 MV Van de Graaff accelerator. In recent experimental campaigns, due to the low neutron yield at EAST, a new shielding device was designed and located as close as possible to the tokamak to enhance the count rate of the spectrometer. The fluence of neutrons and gamma-rays was measured with the liquid neutron spectrometer and was consistent with 3He proportional counter and NaI (Tl) gamma-ray spectrometer measurements. Plasma ion temperature values were deduced from the neutron spectrum in discharges with lower hybrid wave injection and ion cyclotron resonance heating. Scattered neutron spectra were simulated by the Monte Carlo transport Code, and they were well verified by the pulse height measurements at low energies.Comment: 19 pages,10 figures, 1 tabl

    Design and optimization of an advanced time-of-flight neutron spectrometer for deuterium plasmas of the large helical device

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    A time-of-flight neutron spectrometer based on the Time-Of-Flight Enhanced Diagnostic (TOFED) concept has been designed and is under development for the Large Helical Device (LHD). It will be the first advanced neutron spectrometer to measure the 2.45 MeV D–D neutrons (DDNs) from helical/stellarator plasmas. The main mission of the new TOFED is to study the supra-thermal deuterons generated from the auxiliary heating systems in helical plasmas by measuring the time-of-flight spectra of DDN. It will also measure the triton burnup neutrons (TBNs) from the d+t reactions, unlike the original TOFED in the EAST tokamak. Its capability of diagnosing the TBN ratios is evaluated in this work. This new TOFED is expected to be installed in the basement under the LHD hall and shares the collimator with one channel of the vertical neutron camera to define its line of sight. The distance from its primary scintillators to the equatorial plane of LHD plasmas is about 15.5 m. Based on Monte Carlo simulation by a GEANT4 model, the resolution of the DDN energy spectra is 6.6%. When projected onto the neutron rates that are typically obtained in LHD deuterium plasmas (an order of 1015 n/s with neutral beam injection), we expect to obtain the DDN and TBN counting rates of about 2.5 · 105 counts/s and 250 counts/s, respectively. This will allow us to analyze the DDN time-of-flight spectra on time scales of 0.1 s and diagnose the TBN emission rates in several seconds with one instrument, for the first time in helical/stellarator plasmas

    Recent Progress of Neutron Spectrometer Development for LHD Deuterium Plasmas

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    The commissioning of three different types of D-D neutron energy spectrometer has been performed in the Large Helical Device (LHD) to accelerate energetic-ion physics studies in a non-axisymmetric system. Because the LHD is equipped with negative-ion-source-based tangential neutral beam injectors (N-NBs) characterized by high energy up to 180∼190 keV, a significant Doppler shift of D-D neutron energy from 2.45 MeV is expected. Two different compact neutron energy spectrometers, i.e., a conventional liquid organic scintillator, designated as EJ-301, and a newly developed Cs2LiYCl6:Ce with 7Li-enrichment called CLYC7, having tangential sightlines, have shown up- and/or down-shifted D-D neutron energy, as expected according to the direction of N-NB injection. In addition, with the aim of study on a perpendicular energetic ion tail, created by wave heating with ion cyclotron resonance frequency, a neutron energy spectrometer named the Time of Flight Enhanced Diagnostic (TOFED) is being developed. The TOFED is based on a time-of-flight technique and is characterized by high-energy-resolution and a high-counting-rate capability. Commissioning of the TOFED is now ongoing. Recent advances of neutron energy spectrometer development for LHD deuterium plasmas are described

    Time Dependent DD Neutrons Measurement Using a Single Crystal Chemical Vapor Deposition Diamond Detector on EAST

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    A single crystal chemical vapor deposition (scCVD) diamond detector has been successfully employed for neutron measurements in the EAST (Experimental Advanced Superconducting Tokamak) plasmas. The scCVD diamond detector coated with a 5 ��m6LiF (95%6Li enriched) layer was placed inside a polyethylene moderator to enhance the detection efficiency. The time-dependent neutron emission from deuteron plasmas during neutral beam injection (NBI) heating was obtained. The measured results are compared with that of fission chamber detectors, which always act as standard neutron flux monitors. The scCVD diamond detector exhibits good reliability, stability and the capability to withstand harsh radiation environments despite its low detection efficiency due to the small active volume.National Magnetic Confinement Fusion Science Program of China [2013GB106004, 2012GB101003]; National Natural Science Foundation of China [91226102]SCI(E)EI中国科学引文数据库(CSCD)[email protected]

    Simultaneous measurement of energy spectrum and fluence of neutrons using a diamond detector

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    Abstract Due to the excellent radiation hardness and high–temperature endurance, diamond detectors are suitable for intense neutron measurements and promising for neutron diagnostics of scientific fusion devices. In the present work, simultaneous measurement of energy spectrum and fluence of neutrons using a diamond detector was realized for the first time. The absolute response matrix of the diamond detector was simulated based on detailed analysis of the nuclear reactions and the proper selection of nuclear reaction data. Neutron energy spectra as well as neutron fluences for 5.0, 5.5, 8.5, 9.5 and 10.5 MeV neutrons from d–d reaction were measured using the diamond detector based on the absolute response matrix. The measured neutron energy spectra and neutron fluences are reasonable compared with those detected using a EJ-309 liquid scintillator and a 238U fission chamber, respectively, which verifies the reliability of the present work. Furthermore, the energy spectrum and fluence of a 14.2 MeV d–t neutron source were also measured using the diamond detector. The present work demonstrates the ability of simultaneous measurement of energy spectrum and fluence as well as for both d–d and d–t neutrons using a diamond detector, which is of great significance for neutron diagnostics of scientific fusion devices