Neutron diagnostics, including flux and energy spectrum measurements, have been applied on the experimental advanced superconducting tokamak （EAST）. The absolute calibration of neutron yields has been achieved by a calculation method using the Monte Carlo automatic modeling （MCAM） system and the Monte Carlo N-Particles （MCNP） code. Since the neutron yield is closely related with the ion density and temperature, it is a good measure of plasma performance, especially the wave heating effect. In ion cyclotron range of frequencies （ICRF） experiments, the increase in the ion temperature derived by the neutron yield indicates an effective plasma heating. Minority protons damp a large fraction of the total wave power, and then transfer part of the energy to deuterium by collisions. Neutron spectrum measurements also indicate that no tail is created by high energy deuterons during ICRF heating. However, the ion temperature derived by the neutron yield is consistent with the result by using a poloidal X-ray imaging crystal spectrometer （PXCS）, showing a reliable transport calculation.
Charge exchange recombination spectroscopy （CXRS） based on a diagnostic neutral beam （DNB） installed in the HT-7 tokamak is introduced. DNB can provide a 6 A extracted current at 50 kV for 0.1 s in hydrogen. It can penetrate into the core plasma in HT-7. The CXRS system is designed to observe charge exchange （CX） transitions in the visible spectrum. CX light from the beam is focused onto 10 optical fibers, which view the plasma from -5 cm to 20 cm. The CXRS system can measure the ion temperature as low as 0.1 keV. With CXRS, the local ion temperature profile in HT-7 was obtained for the first time.
石跃江符佳李颖颖William ROWAN黄河王福地高慧贤黄娟周倩刘胜张健李军谢远来刘智民黄懿赟胡纯栋万宝年DNB team
Characteristics of ion temperature measured with charge-exchange recombination spectroscopy （CXRS） were studied in Ohmic, lower-hybrid-wave （LHW） driven and ion-cyclotron- resonance-frequency （ICRF） heated plasmas in HT-7. The results indicate that the central ion temperature T10 follows the one-third power law in the product of central line-averaged density Ne and plasma current Ip in Ohmic discharges and is therefore consistent with the Artsimovich scaling law T10 = K （Ip Bt ne R2）1/3. It is shown that there is an appreciable increase of ion temperature during the operation with both LHW and ICRF and that the increment of ion temperature in those shots is mainly due to the energy transfer via collisions between ions and electrons rather that by direct heating of the ions.
Inward energy transport （pinch phenomenon） in the electron channel is observed in HT-7 plasmas using off-axis ion cyclotron resonance frequency （ICRF） heating. Experimental results and power balance transport analysis by TRANSP code are presented in this article. With the aids of GLF23 and Chang-Hinton transport models, which predict energy diffusivity in experimental conditions, the estimated electron pinch velocity is obtained by experimental data and is found reasonably comparable to the results in the previous study, such as Song on Tore Supra. Density scanning shows that the energy convective velocity in the electron channel has a close relation to density scale length~ which is qualitatively in agreement with Wang＇s theoretical prediction. The parametric dependence of electron energy convective velocity on plasma current is still ambiguous and is worthy of future research on EAST.
In the discharge of EAST tokamak, it is observed that （2, 1） neoclassical tearing mode （NTM） is triggered by mode coupling with a （1, 1） internal mode. Using singular value decomposition （SVD） method for soft X-ray emission and for electron cyclotron emission （ECE）, the coupling spatial structures and coupling process between these two modes are analyzed in detail. The results of SVD for ECE reveal that the phase difference between these two modes equals to zero. This is consistent with the perfect coupling condition. Finally, performing statistical analysis of r1/1, ξ1/1 and w2/1, we find that r1/1 more accurately represents the coupling strength than ξ1/1, and r1/1 is also strongly related to the （2, 1） NTM triggering, where r1/1 is the width of （1, 1） internal mode, ξ1/1 is the perturbed amplitude of （1, 1） internal mode, and w2/1 denotes the magnetic island width of （2, 1） NTM.
Properties of the geodesic acoustic mode （GAM） density fluctuations are studied using two toroidally separated Langnmir triple-probe arrays on the top of HT-7 tokamak. The GAM scenario is identified in the potential fluctuations with the toroidally symmetric structure （n =0） and satisfying the temperature scaling of GAM mode frequency. Some theoretical predictions about the mode features of GAM density fluctuations are verified in our experiments： the toroidal mode number of GAM density fluctuations is n = 0; its amplitude is consistent with the theoretical prediction in a factor of 2; the density and potential fluctuations of GAM is in anti-phase at the top of plasma cross-section. Strong nonlinear interactions are found between GAM density fluctuations and ambient turbulence （AT）. The results support the conclusions that the envelope modulation of potential fluctuations is dominantly caused by the direct regulation of GAM in the generation processing, and the envelope modulation of density fluctuation is due to the GAM shear effect.
Discharge with a plasma current of 1 MA at a line-averaged density of 1.8× 10^19 m^-3 was realized in EAST, a fully superconducting tokamak. The key issues to achieve the discharge with 1 MA plasma current include both early shaping and LHCD assistance during start-up phase to extend the voltage margin of poloidal field （PF） coils for easier plasma control, an optimization of the control methodology for PF coils to avoid over-current fault and a very good wall condition. A better wall condition was achieved mainly by extensive Lithium coating. Both stationary H- mode and diverted plasma discharge of 100 s were also obtained.
Primary physical design of the Thomson scattering system for EAST, including the configuration of the system and the design considerations of different sections of the system, is presented. The expected measurability of this design, namely an electron temperature of 513 eV to 5 keV and a plasma density beyond 0.5× 10^19 m^-3, fulfills the requirements of the EAST operation.
The experimental advanced superconducting tokamak （EAST） is the first full superconducting tokamak with a D-shaped cross-sectional plasma presently in operation. Its poloidal coils are relatively far from the plasma due to the necessary thermal isolation from the superconducting magnets, which leads to relatively weaker coupling between plasma and poloidal field. This may cause more difficulties in controlling the vertical instability by using the poloidal coils. The measured growth rates of vertical stability are compared with theoretical calculations, based on a rigid plasma model. Poloidal beta and internal inductance are varied to investigate their effects on the stability margin by changing the values of parameters αn and γn（Howl et al 1992 Phys. Fluids B 4 1724）, with plasma shape fixed to be a configuration with k = 1.9 and 5 = 0.5. A number of ways of studying the stability margin are investigated. Among them, changing the values of parameters κ and li is shown to be the most effective way to increase the stability margin. Finally, a guideline of stability margin Ms（ki, li, A） to a new discharge scenario showing whether plasmas can be stabilized is also presented in this paper.
