Jinxiang Chen

Diagnosing NB plasmas on the EAST tokamak with new time-of-flight neutron spectrometer

The new neutron spectrometer time-of-flight enhanced diagnostics (TOFED) for the EAST tokamak is presented and its characteristics are described in terms of simulation results, as well as the interface in the torus hall along with new neutral beam (NB) injectors. The use of TOFED for studies of the slowing down of NB-injected deuterons is illustrated. The implications of measuring the neutron emission on a long pulse machine are discussed together with the experimental challenges and diagnostic possibilities approaching those to be encountered in continuous operation.

Neutron energy spectrum measurements with a compact liquid scintillation detector on EAST

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 γ-rays was measured with the liquid neutron spectrometer and was consistent with 3He proportional counter and NaI(Tl) γ-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.

Differential cross-section measurement for the {sup 6}Li(n,t){sup 4}He reaction at 3.67 and 4.42 MeV

Abstract A gridded ionization chamber was used to measure the differential cross sections for tritons from the 6Li(n,t)4He reaction at 3.67 and 4.42 MeV. Neutrons were produced via the D(d,n)3He reaction. The absolute neutron flux was determined through the 238U(n,f) and H(n,p) reactions. At 3.67 MeV the result is almost 90 deg symmetric, but it is obviously forward peaked at 4.42 MeV in the center-of-mass reference system.

The effect of low-energy neutrons on activation cross-section measurement

The effect of low-energy neutrons on activation cross-section measurements was analyzed carefully and proved by the measured neutron spectra of T(d,n) 4 He and D(d,n) 3 He reactions. The 58 Ni(n,p) 58m+g Co and 64 Zn(n,p) 64 Cu reactions were used to confirm this analysis, and their cross sections were measured accurately. In addition, their evaluated excitation functions are given.

A compact stilbene crystal neutron spectrometer for EAST D-D plasma neutron diagnostics

A new compact stilbene crystal neutron spectrometer has been investigated and applied in the neutron emission spectroscopy on the EAST tokamak. A new components analysis method is presented to study the anisotropic light output in the stilbene crystal detector. A Geant4 code was developed to simulate the neutron responses in the spectrometer. Based on both the optimal light output function and the fitted pulse height resolution function, a reliable neutron response matrix was obtained by Geant4 simulations and validated by 2.5 MeV and 14 MeV neutron measurements at a 4.5 MV Van de Graaff accelerator. The spectrometer was used to diagnose the ion temperature in plasma discharges with lower hybrid wave injection and ion cyclotron resonance heating on the EAST tokamak.

Cross-section measurement for the 10B(n, α)7Li reaction at 4.0 and 5.0 MeV

Cross-sections of the (10)B(n, alpha)(7)Li reaction were measured at En=4.0 and 5.0 MeV. A gridded ionization chamber (GIC) was used as charged particle detector. Neutrons were produced through the D(d, n)(3)He reaction with a deuterium gas target. Experiments were performed at the 4.5 MV Van de Graaff accelerator of Peking University. Cross-section data of the (238)U(n, f) reaction were employed as standard. The measured cross-sections of the (10)B(n, alpha)(7)Li reaction at 4.0 and 5.0 MeV are 211+/-17 and 169+/-14 mb, respectively, and they are compared with existing results of measurements and evaluations.

Differential cross-section measurement for the 64Zn(n,α)61Ni reaction at 5.03 and 5.95 MeV

Abstract Differential cross sections of the 64Zn(n,α)61Ni reaction were measured at neutron energies of 5.03 and 5.95 MeV by using a gridded ionization chamber. The experiment was performed at the 4.5-MV Van de Graaff accelerator of the Institute of Heavy Ion Physics, Peking University. Neutrons were produced through the D(d,n)3He reaction with a deuterium gas target. The absolute neutron flux was determined by the 238U(n,f) reaction and a calibrated BF3 long counter. Present results are compared with existing data.

Digital discrimination of neutrons and gamma-rays in organic scintillation detectors using moment analysis

Digital discrimination of neutron and gamma-ray events in an organic scintillator has been investigated by moment analysis. Signals induced by an americium-beryllium (Am/Be) isotropic neutron source in a stilbene crystal detector have been sampled with a flash analogue-to-digital converter (ADC) of 1 GSamples/s sampling rate and 10-bit vertical resolution. Neutrons and gamma-rays have been successfully discriminated with a threshold corresponding to gamma-ray energy about 217 keV. Moment analysis has also been verified against the results assessed by a time-of-flight (TOF) measurement. It is shown that the classification of neutrons and gamma-rays afforded by moment analysis is consistent with that achieved by digital TOF measurement. This method has been applied to analyze the data acquired from the stilbene crystal detector in mixed radiation field of the HL-2A tokamak deuterium plasma discharges and the results are described.

Differential cross-section measurement for the 10B(n, α)7Li reaction

Abstract The differential cross sections of the 10B(n, α)7Li reaction were measured at 4.17, 5.02, 5.74, and 6.52 MeV by using a gridded ionization chamber. Neutrons were produced through the D(d,n)3He reaction. The absolute neutron flux was determined through the 238U(n,f) reaction. The experiment shows that as the neutron energy increases from 4.17 to 6.52 MeV, the differential cross section changes from almost 90-deg symmetry to obviously backward peaked in the center-of-mass reference system.

Data acquisition system with pulse height capability for the TOFED time-of-flight neutron spectrometer

A new time-of-flight neutron spectrometer TOFED has been constructed for installation at Experimental Advanced Superconducting Tokamak. A data acquisition system combining measurements of flight time and energy from the interaction of neutrons with the TOFED scintillators has been developed. The data acquisition system can provide a digitizing resolution better than 1.5% (to be compared with the >10% resolution of the recoil particle energy in the plastic scintillators) and a time resolution <1 ns. At the same time, it is compatible with high count rate event recording, which is an essential feature to investigate phenomena occurring on time scales faster than the slowing down time (≈100 ms) of the beam ions in the plasma. Implications of these results on the TOFED capability to resolve fast ion signatures in the neutron spectrum from EAST plasmas are discussed.