If βN exceeds no-wallβN, the plasma will be unstable because of external kink and resistive wall mode(RWM). In this article, the effect of the passive structure and the toroidal rotation on the RWM stability in the experimental advanced superconducting tokamak(EAST) are simulated with CHEASE and MARS codes. A model using a one-dimensional(1D)surface to present the effect of the passive plate is proved to be credible. The no wall βN limit is about 3li, and the ideal wall βN limit is about 4.5li on EAST. It is found that the rotation near the q = 2 surface and the plasma edge affects the RWM more.
As the power available in the initial phase of the ITER operation will be limited, accessing the high confinement mode (H-mode) with low heating power will be a critical issue. In the recent experiment on EAST, the H-mode was obtained for the first time with lower hybrid current drive (LHCD) wave only. Reciprocating Langmuir probe measurements at the outer midplane showed that the electron density n e and electron temperature T e in the scrape-off layer (SOL) were significantly reduced in the ELM-free phase, resulting in the increase of lower-hybrid wave (LHW) reflection. It was found that the power loss P loss was comparable during the L-H transition, by comparing the adjacent L-mode and H-mode discharge. The Dα emission, T e and n e decreased rapidly in the time scale of about 1 ms, and the radial electric field E r turned positive in this process near the last closed flux surface. Multiple L-H-L transitions were observed during a single shot when the applied LHW power was marginal to the threshold. The floating potential (Vf ) had negative spikes corresponding with the Dα signal, and E r oscillation evolved into several intermittent negative spikes just before the L-H transition. In some shots, dithering was observed just before the L-H transition.
Experimental progress of lower hybrid current drive(LHCD)and ion Bernsteinwave(IBW)heating was achieved significantly in HT-7.Long pulse plasmas,up to 400 s,wereobtained by LHCD.High power lower hybrid wave(LHW),with P_(lhw)of 800 kW at 2.45 GHz,was launched and the current drive efficiency was studied for different wave powers.Electrontemperature and Z_(eff)were measured in LHCD discharges.Heating experiment and recent resultsof high power ion Bernstein wave,with P_(ibw)of 600 kW at 27 MHz,were summarized.
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.
Ion’s toroidal velocity,v_t,in both the outermost 4 cm of the confined region and thescrap-off layer of Ohmic L-mode plasmas in EAST was measured using Mach probes.At about1 cm inside the separatrix a local minimum in v_t was observed,from which a cocurrent rotationincreased both inwards and outwards.The radial width of the v_t dip was 1 cm to 2 cm,andboth the density and electron temperature profiles exhibited steep gradients at this dip position.It was observed in both divertor and limiter configurations.To find out its origin,the toroidaltorques induced by neutral friction,neoclassical viscosity,collisional perpendicular shear viscosity,ion orbit loss and turbulent Reynolds stress were estimated using the measured parameters.Ourresults indicate that in this particular parameter regime the neutral friction was the dominantdamping force.The calculated cocurrent toroidal torque by the neoclassical viscosity dominatesover those from the collisional perpendicular shear viscosity,ion orbit loss and turbulent Reynoldsstress.These results are potentially important for the understanding of boundary conditions forthe intrinsic toroidal momentum in tokamak plasmas.
Intermittent convective transport at the edge and in the scrape-off layer(SOL)ofEAST was investigated by using fast reciprocating Langmuir probe.Holes,as part of plasmastrTictures,were detected for the first time inside the shear layer.The amplitude probabilitydistribution function of the turbulence is strongly skewed,with positive skewed events("blobs")prevailing in the SOL region and negative skewed events("holes")dominant inside the shearlayer.The statistical properties coincide with previous observations from JET.The generationmechanism of blobs and holes is also discussed.In addition burst structure and dynamics characterof them are also presented.
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 effect of passive plates on vertical displacement control in the EAST tokamak is investigated by open loop experiments and numerical simulations based on a rigid displacement model.The experiments and simulations indicate that the vertical instability growth rate is reduced by a factor of about 2 in the presence of the passive plates,where the adjacent segments are not connected to each other.The simulations also show that the vertical instability growth rate is reduced by a factor of about 10 if all adjacent segments on each passive plate loop are connected to each other.The operational window is greatly enlarged with the passive plates.
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.
