Electron Cyclotron Resonance Heating Injection Research Articles

Influence of toroidal rotation from electron cyclotron resonance heating in KSTAR

Toroidal rotation behaviors from electron cyclotron resonance heating (ECH) injected Ohmic and high confinement mode (H-mode) plasmas are investigated in KSTAR. The on-axis ECH injection induces core toroidal rotation reversal by neoclassical toroidal viscosity (NTV) damping torque coincided with trapped electron mode (TEM)-driven co-current rotation torque in the countercurrent rotating Ohmic plasmas. In the ECH triggered H-mode plasmas with enhanced heating power, the toroidal rotation in the central region turns to the countercurrent direction and co-current direction in the outer region of the plasma.

Suppression of molybdenum impurity accumulation in the core using on-axis electron cyclotron resonance heating in EAST

Core metal impurity transport in an electron cyclotron resonance heating (ECRH) plasma is investigated for the first time in experimental advanced superconducting tokamak, on the basis of profile measurements of impurity emissions using space-resolved extreme ultraviolet spectroscopy. A significant reduction in the core molybdenum emissivity is observed during the on-axis ECRH phase, accompanied by decreased core electron density and increased electron temperature. The impurity transport study before and during ECRH injection is performed using line emissions of Mo XXIX, Mo XXX, Mo XXXI, and Mo XXXII with the core impurity transport code, STRAHL. It is found that the diffusion coefficient increases substantially and that the value of the diffusion coefficient is about one order of magnitude higher than that of neoclassical transport. Also, the inward convective velocity decreases and even changes its direction in the core region (ρ < 0.5) during on-axis ECRH, which is thought to dominantly contribute to the reduction in core impurity ion density.

Study of Plasma Behavior during ECRH Injection in the GAMMA 10 SMBI Experiments

Establishment of fueling system is one of the critical issues for the future fusion reactors. Fueling experiment supersonic molecular beam injection (SMBI) have been carried out in the central-cell of GAMMA 10. In GAMMA 10, electron cyclotron resonance heating (ECRH) is used at plug/barrier-cells for the formation of the axial confining potential. Recently, ECRH was applied during SMBI to plug the loss particles and increased the plasma density in the central-cell compared to without ECRH. This result suggests that the particles are confined during SMBI due to the injection of ECRH at plug/barrier-cells in GAMMA 10.

Recent progress of RF-dominated experiments on EAST

The research of EAST program is mostly focused on the development of high performance steady state scenario with ITER-like poloidal configuration and RF-dominated heating schemes. With the enhanced ITER-relevant auxiliary heating and current drive systems, the plasma profile control by coupling/integration of various combinations has been investigated, including lower hybrid current drive (LHCD), electron cyclotron resonance heating (ECRH) and ion cyclotron resonance heating (ICRH). The 12 MW ICRH system has been installed on EAST. Heating and confinement studies using the Hydrogen Minority Heating scheme have been investigated. One of the importance challenges for EAST is coupling higher power into the core plasma, experiments including changing plasma position, electron density, local gas puffing and antenna phasing scanning were performed to improve ICRF coupling efficiency on EAST. Results show that local gas injection and reducing the k|| can improve the coupling efficiency directly. By means of the 4.6 GHz and 2.45 GHz LHCD systems, H-mode can be obtained and sustained at relatively high density, even up to ne ∼ 4.5 × 1019 m-3 , where a current drive effect is still observed. Meanwhile, effect of source frequency (2.45GHz and 4.6GHz) on LHCD characteristic has been studied on EAST, showing that higher frequency improves penetration of the coupled LH (lower hybrid) power into the plasma core and leads to a better effect on plasma characteristics. Studies demonstrate the role of parasitic effects of edge plasma in LHCD and the mitigation by increasing source frequency. Experiments of effect of LH spectrum and plasma density on plasma characteristics are performed, suggesting the possibility of plasma control for high performance. The development of a 4MW ECRH system is in progress for the purpose of plasma heating and MHD control. The built ECRH system with 1MW source power has been successfully put into use on EAST in 2015. H-mode discharges with L-H transition triggered by ECRH injection were obtained and its effects on the electron temperature, particle confinement and the core MHD stabilities were observed. By further exploring and optimizing the RF combination for the sole RF heating and current drive regime, fully non-inductive H-mode discharges with Vloop ∼0V has progressed steadily in the 2016 campaign. The overview of the significant progress of RF dominated experiments is presented in this paper.

Toroidal rotation profile structure in KSTAR L-mode plasmas with mixed heating by NBI and ECH

The structure of the toroidal rotation profile with mixed heating by neutral beam injection (NBI) and electron cyclotron resonance heating (ECH) has been investigated in KSTAR L-mode plasmas. ECH with varying resonance layer positions was used for heating a mix control. The experimental results show that ECH causes a counter-current rotation increment both for off-axis and on-axis ECH heating. For L-mode plasmas, off-axis ECH produces larger counter-current rotation than on-axis ECH. Analysis of ion heat and momentum transport for the ECH L-mode plasmas shows that the electron temperature gradient is the main reason for the degradation of ion heat confinement and also the main driving force for the non-diffusive momentum flux. As a possible mechanism for the counter-current intrinsic torque with ECH, the transition of the turbulence mode from ion temperature gradient (ITG) to the trapped electron mode (TEM) with the resulting sign change of turbulence driven residual stress is suggested. A linear gyro-kinetic analysis shows the ITG → TEM transition occurs in a localized region during ECH injection, and the trend of TEM excitation is consistent with the observed macroscopic trend of the toroidal rotation.

Local and Fast Density Pump-out by ECRH in the LHD

A decrease in the electron density is observed during high-power heating, particularly in electron cyclotron resonance heating (ECRH). One possible mechanism is the increase in the number of trapped particles, which can enhance the radial particle flux, because ECRH accelerates electrons in a direction perpendicular to the magnetic field lines. To observe the effects of the production of trapped particles, high-power (1MW) ECRH was applied at the ripple bottom of the magnetic field strength, where trapped particles are readily produced. A rapid local outward flux of electrons was first observed near the heating position shortly after ECRH injection. The outward flux is proportional to the electron density in the density range of 0.4 × 1019 to 0.8 × 1019 m−3. The inward electron flux was subsequently enhanced in the core region.

Investigation of Plasma Behavior during the ECRH Injection in GAMMA 10

Electron Cyclotron Resonance Heating (ECRH) is used for the formation of the axial confining potential by plug/barrier-ECRH (P/B-ECRH) and for the bulk electron heating in the central-cell by central-ECRH (C-ECRH) in GAMMA 10. The plasma performance was increased with ECRHs injection. However the degradation of the plasma parameter was occasionally observed during C-ECRH injection. Increase of the number of the loss particle was also observed at the same time. The mechanism of the degradation of the plasma parameter was investigated in terms of the particle balance.

ECRH Superposition on Linear Cylindrical Helicon Plasma in the LMD-U

Electron cyclotron resonance heating (ECRH) is superimposed on a linear cylindrical helicon plasma in the Large Mirror Device-Upgrade (LMD-U) to study the fluctuation characteristics of high density helicon plasma with/without ECRH injection. The radial profiles of electron density and electron temperature rose by < 10 %, and the drift wave frequency decreased with the ECRH injection. Bicoherence analysis reveals that the nonlinear interaction between drift waves and broad frequency band components exists with or without ECRH injection.