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.
Diagnostic neutral beam (DNB), combined with spectral diagnostics, is employedto measure the ion temperature in HT-7. The factors affecting the extracted beam are studied inthe experiment for the high performance diagnostic neutral beam. A 6.5 A extracted hydrogencurrent at 43 keV of 100 ms was obtained after optimization. The extracted beam has a protonratio as high as 40%, and can penetrate into the core plasma after neutralization to measure theion temperature effectively.
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 recombinationspectroscopy （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 iontemperature Ti0 follows the one-third power law in the product of central line-averaged densityne and plasma current Ip in Ohmic discharges and is therefore consistent with the Artsimovichscaling law Ti0 = K· （Ip· Bt·ne · R2）1/3.It is shown that there is an appreciable increase ofion temperature during the operation with both LHW and ICRF and that the increment of iontemperature in those shots is mainly due to the energy transfer via collisions between ions andelectrons 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 γ_(1/1),ζ_(1/1) and ω_(2/1),we find that γ_(1/1) more accurately represents the coupling strength than ζ_(1/1),and γ_(1/1) is also strongly related to the(2,1) NTM triggering,where γ_(1/1) is the width of(1,1) internal mode,ζ_(1/1) is the perturbed amplitude of(1,1) internal mode,and ω_(2/1) denotes the magnetic island width of(2,1) NTM.
Properties of the geodesic acoustic mode (GAM) density fluctuations are studiedusing two toroidally separated Langmuir triple-probe arrays on the top of HT-7 tokamak. TheGAM 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 predictionsabout 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 withthe theoretical prediction in a factor of 2; the density and potential fluctuations of GAM is inanti-phase at the top of plasma cross-section. Strong nonlinear interactions are found betweenGAM density fluctuations and ambient turbulence (AT). The results support the conclusions thatthe envelope modulation of potential fluctuations is dominantly caused by the direct regulation ofGAM in the generation processing, and the envelope modulation of density fluctuation is due tothe GAM shear effect.
Discharge with a plasma current of 1 MA at a line-averaged density of 1.8× 1019m-3was realized in EAST,a fully superconducting tokamak.The key issues to achieve the dischargewith 1 MA plasma current include both early shaping and LHCD assistance during start-up phaseto extend the voltage margin of poloidal field （PF）coils for easier plasma control,an optimizationof 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 theconfiguration of the system and the design considerations of different sections of the system, ispresented. The expected measurability of this design, namely an electron temperature of 50 eV to5 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 di?culties 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 δ = 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(κ,li,A) to a new discharge scenario showing whether plasmas can be stabilized is also presented in this paper.
