[en] The nuclear radiation have come an important issue after the NBI heating system successful operation on EAST device. Massive DD neutrons produce from beam-thermal reaction are need effective measurement and shielding to safeguard for human and environment. Thirteen sites of dose monitoring arrangement on the sensitive district to online acquisition the neutron and gamma dose rate, and provide light and sound alarm during the dose rate exceed configured threshold. The EAST device shielding by 1.5 meters of concrete wall and the vacuum chamber wall interbed injection water to prevent the fusion neutron leaking into the environment. The monitoring data show that the neutron and gamma ray dose rates are around the natural background level. (author)

[en] Gamma spectrum and fluence measurements on HT-7 superconducting Tokamak were described. Rich gamma radiation behaviors were observed under different plasma experimental conditions. The primary results from analyses of gamma spectrum and fluence data under Ohmic heating (OH), lower hybrid wave (LHW) heating, ion-cyclotron resonance frequency (ICRF) heating, ion Bernstein wave (IBW) and long pulse operation conditions are presented. (authors)

[en] Measurements of the neutron flux distribution have been performed and presented in this paper. Two kinds of neutron detector system based on high gamma-resistant BF₃ and ³He proportional counters, associated electronics and data acquisition system were sued in the experiments. In HT-7 2005 spring campaign, the neutron fluxes of different horizontal and vertical positions outside the vacuum vessel were measured and analyzed in detail under the same discharge conditions. The influences of the existence of the vacuum vessel and the iron-core transformer were studied. The consistency between the measurement and the three-dimensional numerical calculations has been proved. (authors)

[en] The faster time resolved neutron flux real time measurement system was composed by higher sensitivity "2"3"5U fission chamber detector. That has to be capable of investigating the auxiliary heating of Radio Frequency (RF) wave and evaluating the synthetical property of fusion plasma through by monitor fusion neutron and photo-neutron during the plasma discharge on (Experimental Advanced Superconducting Tokamak) EAST tokamak. The "2"3"5U fission chamber measurement result had a similar trend to that of "3He proportional counter, furthermore, it has lower sensitivity to γ-rays and wider counts rate range. (authors)

[en] Five channels of time-resolved neutron flux monitor system have accomplished construction by ³He proportion counter and ²³⁵U fission chamber. That was be used for study neutron emission behavior at the initial stage of deuterium plasma experiment on EAST tokamak. At the condition of ohmic discharge, more of photo-neutrons production with low density during the plasma current ramp-up stage. Just increase the central chord average of electron density over 2.0x10¹⁹m^-3, photo-neutron could be availably elimination. The power of lower hybrid wave (LHW) feed-in plasma excess a threshold has ideal effective for reduce loop voltage and photo-neutron, which power strong enough and plasma background parameter higher case that more fusion neutron production. Flux monitor system detected plenty of fusion neutrons during the Ion-cyclotron resonance frequency (ICRF) valid heating plasma. (author)

[en] Background: During the experiment of Experimental Advanced Superconducting Tokamak (EAST), reaction of D-D may generate neutrons with energy of 2.45 MeV, and bremsstrahlung gamma rays and neutron activated gamma rays as well. Purpose: The aim is to study the radiation of neutrons and gamma rays in the EAST hall during the running of EAST tokamak and obtain the radiation doses under different modes and parameters by implementing a radiation monitoring system to diagnose some plasma parameters and ensure the radiation safety of the personnel and the environment around EAST. Methods: In consideration of the highly and transient radiation doses of neutrons and gamma rays contrast to the lowly environmental background during the plasma discharge in the EAST hall, the combination of high ranging and fast responding detectors are adopted in the EAST hall whilst high sensitivity and stability detectors are deployed in the environment. Thirteen monitoring points were selected around the EAST, each point contains a neutron detector and a gamma ray detector. Combination of Ethernet and twisted pair are adopted for the data transmission, and the radiation monitoring software based on LabVIEW was developed. Results: A radiation monitoring system of EAST tokamak was successfully built to monitor and save the real-time radiation dose rates of each detector, and to produce an alarm signal when abnormal dose rate happens. The radiation monitoring system had run stably for more than three months during the EAST experiment in the spring of 2015, and obtained many useful experimental data on fusion radiation safety and protection. Conclusion: The radiation monitoring system can well monitor the radiation around the EAST tokamak, and provide a platform for the future study of radiation safety and protection of the fusion reactor. (authors)

[en] An analysis of the neutron activation and shutdown dose rates was performed for the EAST high-power deuterium neutral beam injector test facility (EAST NBITF) by using the multiparticle transport code FLUKA 2011.2. Also, the neutron and neutron-induced gamma spectra of the facility's vacuum vessel were evaluated. The results identified the major radionuclides ⁹⁹Mo, ⁶⁵Ni, ⁵⁸Co, ⁵⁶Mn, and ⁵¹Cr for the vacuum vessel and the primary nuclide ⁶⁴Cu for both the ion dump and the calorimeter. The simulated results indicated that, when the EAST NBITF operates within the design parameters of deuterium energy 80 keV, current 50 A, and pulse 100 s, the neutron intensity will achieve 10¹¹ n/s with no radiation safety problems after the EAST NBITF shuts down. (authors)

[en] For suppressing the energy of runaway electrons in tokamak plasma, we analyzed the X-ray energy spectra by runaway electrons in different discharges of the HT-7 tokamak experiment performed in the autumn of 2009. The resonant phenomenon between runaway electrons and magnetic ripple was found. Although, the energy of runaway electrons in the plasma core can be as high as several tens of MeV, but when they are transported to the edge, the electron energy are limited to a certain range by resonance with the magnetic ripple of different harmonic numbers. The runaway electrons under high loop voltage resonate with low step magnetic perturbations, with high energy gain; whereas the runaway electrons under low loop voltage resonate with high level magnetic perturbations, with low energy gain. Using this mechanism, the energy of runaway electrons can be restricted to a low level, and this will significantly mitigate the damage effect on the equipment caused by runaway electrons. (authors)

[en] For the safe operation and maintenance of neutral beam injector (NBI), specific activity and shutdown contact dose rate of the sample material SS316 are estimated around the experimental advanced superconducting tokamak (EAST) neutral beam port. Firstly, the neutron emission intensity is calculated by TRANSP code while the neutral beam is co-injected to EAST. Secondly, the neutron activation and shutdown contact dose rates for the neutral beam sample materials SS316 are derived by the Monte Carlo code MCNP and the inventory code FISPACT-2007. The simulations indicate that the primary radioactive nuclides of SS316 are ⁵⁸Co and ⁵⁴Mn. The peak contact dose rate is 8.52 × 10⁻⁶ Sv/h after EAST shutdown one second. That is under the International Thermonuclear Experimental Reactor (ITER) design values 1 × 10⁻⁵ Sv/h. - Highlights: • The neutron intensity of EAST plasma centre is increased to 1.0 × 10¹⁴ n/s when the neutral beam with energy 58 keV is injected into EAST plasma with line-averaged density 3.0 × 10¹³ /cm³. • The beam-target reaction is the main contribution to the total neutron emission under the EAST current operating condition. • The shutdown contact dose rate at the sample material is 8.52 × 10⁻⁶ Sv/h after shutdown one second. That implies the personal can access to NBI system for maintenance and repair after EAST shutdown.

[en] Neutron emission in EAST was investigated by a time-resolved monitor system which consists of four ³He proportional counters and a ²³⁵U fission chamber. The D-D neutron flux increased approximately an order of magnitude during the 27 MHz ion-cyclotron radio frequency (ICRF) heating, demonstrating that the ICRF wave heated the plasma effectively. In addition in lower hybrid wave (LHW) experiment with higher plasma parameters D-D neutrons were also detected. However, masses of photoneutrons were generated in Ohmic discharges with low plasma density. Effect of plasma density on the production of photoneutrons was studied, and it is found that LHW can suppress the generation of the runaway electrons and reduce the share of the photoneutrons effectively. (magnetically confined plasma)