J. F. Chang

Divertor asymmetry and scrape-off layer flow in various divertor configurations in Experimental Advanced Superconducting Tokamak

Divertor asymmetry and its dependence on the ion ▿B direction has been investigated in the Experimental Advanced Superconducting Tokamak by changing the divertor configuration from lower single null (LSN), via double null (DN), to upper single null (USN) during one single discharge. Divertor plasmas exhibit the usual in-out asymmetry in particle and heat fluxes in LSN with the ion ▿B direction toward the lower X-point, favoring the outer divertor, especially at high density. The in-out asymmetry is reversed when changing the divertor configuration from LSN to USN, thus clearly demonstrating the effect of classical drifts. DN exhibits an even stronger in-out divertor asymmetry, favoring the outer divertor. A significant top-down asymmetry is also seen for DN, with greater particle and heat fluxes to the bottom divertor. In addition, the parallel plasma flow has been measured by a fast moving Mach probe at the outer midplane, which shows similar magnitude to the Pfirsch-Schluter flow. Its contribution to th...

First observation of a new zonal-flow cycle state in the H-mode transport barrier of the experimental advanced superconducting Tokamak

A new turbulence-flow cycle state has been discovered after the formation of a transport barrier in the H-mode plasma edge during a quiescent phase on the EAST superconducting tokamak. Zonal-flow modulation of high-frequency-broadband (0.05–1u2009MHz) turbulence was observed in the steep-gradient region leading to intermittent transport events across the edge transport barrier. Good confinement (H98y,2u2009∼u20091) has been achieved in this state, even with input heating power near the L-H transition threshold. A novel model based on predator-prey interaction between turbulence and zonal flows reproduced this state well.

Real-time measurements for edge plasma parameters using triple probes on EAST

The achievement of the first plasma has demonstrated that the Experimental Advanced Superconducting Tokamak (EAST) engineering construction is completely successful. Divertor plasma discharge with double null configuration was achieved and verified by the fitting codes. Arrays of 60 tilted divertor probes have been installed in the lower, both inboard and outboard, divertor plates of EAST. Evolution of electron temperature and density is obtained by using triple-probe systems; real-time particle flux and power flux at divertor target plates have been measured. Tilted Langmuir triple probes (TLTPS) have been successfully used for measuring edge plasma parameters. The strike point by the fitting codes coincides well with measured edge plasma parameters.

Validation of fast-ion D-alpha spectrum measurements during EAST neutral-beam heated plasmas

To investigate the fast ion behavior, a fast ion D-alpha (FIDA) diagnostic system has been installed on EAST. Fast ion features can be inferred from the Doppler shifted spectrum of Balmer-alpha light from energetic hydrogenic atoms. This paper will focus on the validation of FIDA measurements performed using MHD-quiescent discharges in 2015 campaign. Two codes have been applied to calculate the Dα spectrum: one is a Monte Carlo code, Fortran 90 version FIDASIM, and the other is an analytical code, Simulation of Spectra (SOS). The predicted SOS fast-ion spectrum agrees well with the measurement; however, the level of fast-ion part from FIDASIM is lower. The discrepancy is possibly due to the difference between FIDASIM and SOS velocity distribution function. The details will be presented in the paper to primarily address comparisons of predicted and observed spectrum shapes/amplitudes.

Implementation and first application of EMC3-EIRENE to EAST double-null divertor

The 3D edge Monte Carlo code coupled with EIRENE (EMC3-EIRENE) has been implemented on the Experimental Advanced Superconducting Tokamak (EAST) and, for the first time, applied to an axisymmetric double null divertor plasma. The code results are compared with Langmuir probe measurements. The cross-field transport coefficients for particle and energy, D⊥ and χ⊥, are determined by fitting the electron density and temperature profiles measured by a reciprocating probe on the outboard midplane. Good agreement between the simulation and probe profiles is obtained when D⊥ and χ⊥ are set to be 0.4 m2 s−1 and 2 m2 s−1, respectively. However, considerable discrepancies in density and temperature profiles are observed downstream. A parameter sensitivity study is carried out to identify the possible causes. Analyzing the numerical results in comparison with the measurements leads to the conclusion that the real separatrix at the outer midplane tends to be located ~7 mm inward with respect to the last closed flux surface obtained from the equilibrium fitting code.

Fast-ion Dα spectrum diagnostic in the EAST

In toroidal magnetic fusion devices, fast-ion D-alpha diagnostic (FIDA) is a powerful method to study the fast-ion feature. The fast-ion characteristics can be inferred from the Doppler shifted spectrum of Dα light according to charge exchange recombination process between fast ions and probe beam. Since conceptual design presented in the last HTPD conference, significant progress has been made to apply FIDA systems on the Experimental Advanced Superconducting Tokamak (EAST). Both co-current and counter-current neutral beam injectors are available, and each can deliver 2-4 MW beam power with 50-80 keV beam energy. Presently, two sets of high throughput spectrometer systems have been installed on EAST, allowing to capture passing and trapped fast-ion characteristics simultaneously, using Kaiser HoloSpec transmission grating spectrometer and Bunkoukeiki FLP-200 volume phase holographic spectrometer coupled with Princeton Instruments ProEM 1024B eXcelon and Andor DU-888 iXon3 1024 CCD camera, respectively. This paper will present the details of the hardware descriptions and experimental spectrum.

Measurement of the deuterium Balmer series line emission on EAST

Volume recombination plays an important role towards plasma detachment for magnetically confined fusion devices. High quantum number states of the Balmer series of deuterium are used to study recombination. On EAST (Experimental Advanced Superconducting Tokamak), two visible spectroscopic measurements are applied for the upper/lower divertor with 13 channels, respectively. Both systems are coupled with Princeton Instruments ProEM EMCCD 1024B camera: one is equipped on an Acton SP2750 spectrometer, which has a high spectral resolution ∼0.0049 nm with 2400 gr/mm grating to measure the Dα(Hα) spectral line and with 1200 gr/mm grating to measure deuterium molecular Fulcher band emissions and another is equipped on IsoPlane SCT320 using 600 gr/mm to measure high-n Balmer series emission lines, allowing us to study volume recombination on EAST and to obtain the related line averaged plasma parameters (Te, ne) during EAST detached phases. This paper will present the details of the measurements and the characteristics of deuterium Balmer series line emissions during density ramp-up L-mode USN plasma on EAST.

Scintillator-based fast ion loss measurements in the EAST

A new scintillator-based fast ion loss detector (FILD) has been installed on Experimental Advanced Superconducting Tokamak (EAST) to investigate the fast ion loss behavior in high performance plasma with neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH). A two dimensional 40 mm × 40 mm scintillator-coated (ZnS:Ag) stainless plate is mounted in the front of the detector, capturing the escaping fast ions. Photons from the scintillator plate are imaged with a Phantom V2010 CCD camera. The lost fast ions can be measured with the pitch angle from 60° to 120° and the gyroradius from 10 mm to 180 mm. This paper will describe the details of FILD diagnostic on EAST and describe preliminary measurements during NBI and ICRH heating.