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A significant reduction in neutron yield in the plasma core has been observed in EAST neutral beam injection into plasmas with a low-edge safe factor of q 95 = 3.5 and a n = 2 resonant magnetic perturbation (RMP) during a sawtooth crash. Harmonics of the m/n = 1/1 mode (m and n being the poloidal and toroidal mode numbers) develop simultaneously. A sawtooth crash is triggered when the current of the RMP exceeds a critical value; saturated fishbone phase occurs with small RMP currents. Soft x-ray (SXR) tomographic patterns obtained during sawtooth crashes have annular hot-ring shapes outside the q = 1 surface that are similar to those of double tearing modes triggered by off-axis sawtooth crashes in TFTR reversed magnetic shear plasma. M3D nonlinear simulations confirmed the initial penetration of the n = 2 RMP in the plasma core and further demonstrated a complete sawtooth crash with the appearance of a right annular hot ring near the q = 1 surface. Reconstruction of the trajectory of SXR signals before the crash shows chaotic behavior. Moreover, a high-frequency mode was seen to appear just before the sawtooth crash, accompanied by an edge geodesic acoustic mode. This edge mode is free in the saturated fishbone phase. The role of high-frequency mode in the sawtooth crash remains unclear. [ABSTRACT FROM AUTHOR]

A neutron activation system (NAS) has been developed on the Experimental Advanced Superconducting Tokamak (EAST) for the investigation of time-integrated neutron yield. It is a robust neutron diagnostic with high precision and a wide dynamic range. Some high purity materials with a proper nuclear reaction energy threshold and cross section are tested as neutron detectors in the NAS, and they are delivered to the tokamak device by a pneumatic transfer system. The length of the pneumatic pipeline is about 50 m, and the transfer time ranges from 10 s to 20 s. The decay gamma rays of the activated samples are measured with a high-purity germanium spectrometer, and its detection efficiencies are 6.9% at 336 keV and 1.7% at 1779 keV, respectively. Indium and silicon samples with a reaction threshold of 0.3 MeV and 4.0 MeV, respectively, were successfully implemented in the diagnosis of DD and DT neutron yield in the EAST. The neutron flux of the NAS was compared with the count of the fission chamber in the EAST neutral beam injection experiment, and the DD neutron yield evaluated by the NAS ranges from 1.9 × 1012 n/shot to 5.9 × 1014 n/shot during recent experimental campaign. [ABSTRACT FROM AUTHOR]

Two high performance single crystal diamond (SCD) radiation detectors for neutrons and gamma ray have been fabricated. One was coated with a 5 μm 6LiF (95% enriched in 6Li) layer in order to detect the neutrons and the other one is without any conversion layer for comparison. The detectors are irradiated with the 241Am-Be and 252Cf neutron sources and 152Eu gamma source to test their performance. Under neutron sources, the neutron signal peak was clearly observed in the detector with the 6LiF conversion layer. Meanwhile, both detectors are responsive to the gamma rays at the low energy. The 152Eu gamma source was specially used to verify the gamma ray detection ability of the fabricated SCD detectors. The results show that the detector's count rate and the gamma peak center position in the PHS depend on the incident gamma spectra critically. Combined, these results demonstrate that the design and fabrication process of the detectors are feasible. [ABSTRACT FROM AUTHOR]

A single crystal diamond (SCD) detector and a polycrystalline diamond (PCD) detector have been designed and fabricated using electronic grade CVD diamond. The fabricated detectors were tested for their dark current and X-ray photocurrent. It was found that the SCD and PCD detectors have superb signal to noise ratios (SNR) under X-ray irradiation from an Ag target with 10kV and 40kV accelerating voltage, 2000 and 7000 respectively for the SCD detector and 550 and 2000 for the PCD detector. The performance of these detectors using an 241Am α source was tested under different bias voltages and the results were benchmarked against a commercial SCD detector. The typical rise time of an α event in both of the fabricated detectors are about 1.2ns. The fabricated SCD detector has a 3.7% net energy resolution while that of the commercial detector is about 3.9%. The pulse height spectra are integrated and fitted to obtain the charge collection efficiency. For the fabricated SCD detector, this value is above 97% at bias 200V or beyond, which is 1-2% higher than that of the commercial detector at the same voltage. Finally, the fabricated PCD detector can also detect the presence of α particle although it only has a continuous and decreasing energy spectrum under α radiation. These results fully reveal that the fabricated SCD detector has good performance as a multifunctional detector for both X-ray and α radiation, and show great potential as neutron spectrometer as well. [ABSTRACT FROM AUTHOR]

Neutral beam injection (NBI) system has been proved to affect sawtooth activities through both producing energetic particles and supplying torque applied to the plasma. The impact of NBI on sawtooth crashes has been studied in the EAST tokamak, which is equipped with co- and counter NBIs. Statistical analysis shows that both strong co- and counter-NBI yield stronger sawtooth activities than cases when heating power is weak. A minimum sawtooth period is observed at a counter-NBI power of 0.2 MW. This is linked to zero-plasma rotation and a non-rotating precursor mode of the sawtooth instability. This indicates that the sawtooth instability is stabilized by plasma rotation as previously suggested. The fast-ion content differs between co- and counter-NBI, so energetic particles might additionally contribute to the sawtooth activities. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]