A type of silicon detector known as AXUV (absolute extreme ultraviolet) photodiodes is successfully used to measure the radiated power in EAST. The detector is characterized by compact structure, fast temporal response (<0.5 s) and flat spectral sensitivity in the range from ultra-violet to X-ray. Two 16-channel AXUV arrays are installed in EAST to view the whole poloidal cross-section of plasma. Based on the diagnostic system, typical radiation distributions for both limiter and divertor plasma are obtained and compared. As divertor detachment occurs, the radiation distribution in X-point region is observed to vary distinctly. The total radiation power losses in discharges with different plasma parameters are briefly analyzed.
Beta-induced Alfvén eigenmodes (BAEs) during strong tearing modes are investigated on the EAST tokamak systematically, and the relation between the BAE frequencies and plasma parameters such as electron density ne , ion temperature T i , the profile of safety factor q(ρ) or the intensity of Ḃθ (the width of the magnetic island w) is given in detail during the injection of the power of lower hybrid wave (LHW) (or is also accompanied by the injection of ion cyclotron resonance frequency) comprehensively. All the conditions show that the values of BAE frequencies f BAE ∝ (T e + 7 4 T i ) 1/2 are in agreement with the generalized fishbone-like dispersion relation, and the activities of the BAEs have a strong interaction with the process of magnetic reconnection.The BAEs are formed during the injection of the power of LHW, and disappear immediately when the power of LHW is turned off on the EAST tokamak. The LHW plasmas or the runaway discharge in Ohmic plasmas can increase the population of fast electrons, which plays a role in the activities of BAEs and a possible excitation mechanism for the BAEs during the strong tearing mode activities.
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.
A toroidal Alfvén eigenmode (TAE) excited by barely trapped energetic electrons during the application of a static magnetic perturbations (MPs) is observed for the first time in tokamak ohmic heating plasmas. This TAE appears when the current of a static n = 2 MPs exceeds a threshold value, at which a forced n = 2 magnetic reconnection happens. Here, n is the toroidal mode number. This TAE is located near the plasma edge, which agrees with the calculation of the TAE gap. It propagates in the ion diamagnetic direction and has a dominant toroidal mode number n = 2. The frequency of the TAE is consistent with the precessional frequency of the barely trapped energetic electrons with energy around 150 keV. An increase of the hard x-ray emission intensity in this energy range is observed just after the n = 2 magnetic reconnection. The energetic electrons may be accelerated by the magnetic islands formed after reconnection. The TAE is stabilized after a reduction in the contents of energetic electrons. This observation suggests that the application of static MPs may provide us with a novel method to actively control Alfvén eigenmodes in fusion plasmas.
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