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.
Divertor plasma properties for lower single-null (LSN) configuration in EAST, undera water-cooling graphite wall condition, are presented. A typical shot is selected for analyzingelectron temperature, density and power flux at targets. Both higher electron density and lowerelectron temperature are found at the inboard target, compared to those at the outboard target.A higher power flux is also found to be at the outboard target because of in-out asymmetries forLSN-shaped discharge.
A single-channel far-infrared(FIR)laser interferometer was developed to measurethe line averaged electron density on the EAST tokamak.The structure of the single-channelFIR laser interferometer is described in detail.The evolution of density sawtooth oscillation wasmeasured by means the FIR laser interferometer,and was identified by electron cyclotron emission(ECE)signals and soft X-ray intensity.The discharges with and without sawtooth were comparedwith each other in the Hugill diagram.
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.
In this work,population coefficients of hydrogen’s n=3 excited state from thehydrogen collisional-radiative（CR）model,from the data file of DEGAS 2,are used to calculatethe photon emissivity coefficients（PECs）of hydrogen Balmer-α（n=3 → n=2）（Hα）.Theresults are compared with the PECs from Atomic Data and Analysis Structure（ADAS）database,and a good agreement is found.A magnetic surface-averaged neutral density profile of typicaldouble-null（DN）plasma in EAST is obtained by using FRANTIC,the 1.5-D fluid transportcode.It is found that the sum of integral Dα and Hα emission intensity calculated via theneutral density agrees with the measured results obtained by using the absolutely calibratedmulti-channel poloidal photodiode array systems viewing the lower divertor at the last closed fluxsurface（LCFS）.It is revealed that the typical magnetic surface-averaged neutral density at LCFSis about 3.5×1016m-3.
